summaryrefslogtreecommitdiff
path: root/src/viewport.cpp
blob: 13f87de1da535bb78eab1549384dfccf18dbb08a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
/* $Id$ */

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * @file viewport.cpp Handling of all viewports.
 *
 * \verbatim
 * The in-game coordinate system looks like this *
 *                                               *
 *                    ^ Z                        *
 *                    |                          *
 *                    |                          *
 *                    |                          *
 *                    |                          *
 *                 /     \                       *
 *              /           \                    *
 *           /                 \                 *
 *        /                       \              *
 *   X <                             > Y         *
 * \endverbatim
 */

/**
 * @defgroup vp_column_row Rows and columns in the viewport
 *
 * Columns are vertical sections of the viewport that are half a tile wide.
 * The origin, i.e. column 0, is through the northern and southern most tile.
 * This means that the column of e.g. Tile(0, 0) and Tile(100, 100) are in
 * column number 0. The negative columns are towards the left of the screen,
 * or towards the west, whereas the positive ones are towards respectively
 * the right and east.
 * With half a tile wide is meant that the next column of tiles directly west
 * or east of the centre line are respectively column -1 and 1. Their tile
 * centers are only half a tile from the center of their adjoining tile when
 * looking only at the X-coordinate.
 *
 * \verbatim
 *        ╳        *
 *       ╱ ╲       *
 *      ╳ 0 ╳      *
 *     ╱ ╲ ╱ ╲     *
 *    ╳-1 ╳ 1 ╳    *
 *   ╱ ╲ ╱ ╲ ╱ ╲   *
 *  ╳-2 ╳ 0 ╳ 2 ╳  *
 *   ╲ ╱ ╲ ╱ ╲ ╱   *
 *    ╳-1 ╳ 1 ╳    *
 *     ╲ ╱ ╲ ╱     *
 *      ╳ 0 ╳      *
 *       ╲ ╱       *
 *        ╳        *
 * \endverbatim
 *
 *
 * Rows are horizontal sections of the viewport, also half a tile wide.
 * This time the nothern most tile on the map defines 0 and
 * everything south of that has a positive number.
 */

#include "stdafx.h"
#include "landscape.h"
#include "viewport_func.h"
#include "station_base.h"
#include "waypoint_base.h"
#include "town.h"
#include "signs_base.h"
#include "signs_func.h"
#include "vehicle_base.h"
#include "vehicle_gui.h"
#include "blitter/factory.hpp"
#include "strings_func.h"
#include "zoom_func.h"
#include "vehicle_func.h"
#include "company_func.h"
#include "waypoint_func.h"
#include "window_func.h"
#include "tilehighlight_func.h"
#include "window_gui.h"
#include "linkgraph/linkgraph_gui.h"
#include "viewport_sprite_sorter.h"
#include "bridge_map.h"
#include "company_base.h"
#include "command_func.h"
#include "network/network_func.h"
#include "framerate_type.h"
#include "core/sort_func.hpp"

#include <map>

#include "table/strings.h"
#include "table/string_colours.h"

#include "safeguards.h"

Point _tile_fract_coords;


static const int MAX_TILE_EXTENT_LEFT   = ZOOM_LVL_BASE * TILE_PIXELS;                     ///< Maximum left   extent of tile relative to north corner.
static const int MAX_TILE_EXTENT_RIGHT  = ZOOM_LVL_BASE * TILE_PIXELS;                     ///< Maximum right  extent of tile relative to north corner.
static const int MAX_TILE_EXTENT_TOP    = ZOOM_LVL_BASE * MAX_BUILDING_PIXELS;             ///< Maximum top    extent of tile relative to north corner (not considering bridges).
static const int MAX_TILE_EXTENT_BOTTOM = ZOOM_LVL_BASE * (TILE_PIXELS + 2 * TILE_HEIGHT); ///< Maximum bottom extent of tile relative to north corner (worst case: #SLOPE_STEEP_N).

struct StringSpriteToDraw {
	StringID string;
	Colours colour;
	int32 x;
	int32 y;
	uint64 params[2];
	uint16 width;
};

struct TileSpriteToDraw {
	SpriteID image;
	PaletteID pal;
	const SubSprite *sub;           ///< only draw a rectangular part of the sprite
	int32 x;                        ///< screen X coordinate of sprite
	int32 y;                        ///< screen Y coordinate of sprite
};

struct ChildScreenSpriteToDraw {
	SpriteID image;
	PaletteID pal;
	const SubSprite *sub;           ///< only draw a rectangular part of the sprite
	int32 x;
	int32 y;
	int next;                       ///< next child to draw (-1 at the end)
};

/** Enumeration of multi-part foundations */
enum FoundationPart {
	FOUNDATION_PART_NONE     = 0xFF,  ///< Neither foundation nor groundsprite drawn yet.
	FOUNDATION_PART_NORMAL   = 0,     ///< First part (normal foundation or no foundation)
	FOUNDATION_PART_HALFTILE = 1,     ///< Second part (halftile foundation)
	FOUNDATION_PART_END
};

/**
 * Mode of "sprite combining"
 * @see StartSpriteCombine
 */
enum SpriteCombineMode {
	SPRITE_COMBINE_NONE,     ///< Every #AddSortableSpriteToDraw start its own bounding box
	SPRITE_COMBINE_PENDING,  ///< %Sprite combining will start with the next unclipped sprite.
	SPRITE_COMBINE_ACTIVE,   ///< %Sprite combining is active. #AddSortableSpriteToDraw outputs child sprites.
};

typedef SmallVector<TileSpriteToDraw, 64> TileSpriteToDrawVector;
typedef SmallVector<StringSpriteToDraw, 4> StringSpriteToDrawVector;
typedef SmallVector<ParentSpriteToDraw, 64> ParentSpriteToDrawVector;
typedef SmallVector<ChildScreenSpriteToDraw, 16> ChildScreenSpriteToDrawVector;

/** Data structure storing rendering information */
struct ViewportDrawer {
	DrawPixelInfo dpi;

	StringSpriteToDrawVector string_sprites_to_draw;
	TileSpriteToDrawVector tile_sprites_to_draw;
	ParentSpriteToDrawVector parent_sprites_to_draw;
	ParentSpriteToSortVector parent_sprites_to_sort; ///< Parent sprite pointer array used for sorting
	ChildScreenSpriteToDrawVector child_screen_sprites_to_draw;

	int *last_child;

	SpriteCombineMode combine_sprites;               ///< Current mode of "sprite combining". @see StartSpriteCombine

	int foundation[FOUNDATION_PART_END];             ///< Foundation sprites (index into parent_sprites_to_draw).
	FoundationPart foundation_part;                  ///< Currently active foundation for ground sprite drawing.
	int *last_foundation_child[FOUNDATION_PART_END]; ///< Tail of ChildSprite list of the foundations. (index into child_screen_sprites_to_draw)
	Point foundation_offset[FOUNDATION_PART_END];    ///< Pixel offset for ground sprites on the foundations.
};

static void MarkViewportDirty(const ViewPort *vp, int left, int top, int right, int bottom);

static ViewportDrawer _vd;

TileHighlightData _thd;
static TileInfo *_cur_ti;
bool _draw_bounding_boxes = false;
bool _draw_dirty_blocks = false;
uint _dirty_block_colour = 0;
static VpSpriteSorter _vp_sprite_sorter = NULL;

static Point MapXYZToViewport(const ViewPort *vp, int x, int y, int z)
{
	Point p = RemapCoords(x, y, z);
	p.x -= vp->virtual_width / 2;
	p.y -= vp->virtual_height / 2;
	return p;
}

void DeleteWindowViewport(Window *w)
{
	if (w->viewport == NULL) return;

	delete w->viewport->overlay;
	free(w->viewport);
	w->viewport = NULL;
}

/**
 * Initialize viewport of the window for use.
 * @param w Window to use/display the viewport in
 * @param x Offset of left edge of viewport with respect to left edge window \a w
 * @param y Offset of top edge of viewport with respect to top edge window \a w
 * @param width Width of the viewport
 * @param height Height of the viewport
 * @param follow_flags Flags controlling the viewport.
 *        - If bit 31 is set, the lower 20 bits are the vehicle that the viewport should follow.
 *        - If bit 31 is clear, it is a #TileIndex.
 * @param zoom Zoomlevel to display
 */
void InitializeWindowViewport(Window *w, int x, int y,
	int width, int height, uint32 follow_flags, ZoomLevel zoom)
{
	assert(w->viewport == NULL);

	ViewportData *vp = CallocT<ViewportData>(1);

	vp->left = x + w->left;
	vp->top = y + w->top;
	vp->width = width;
	vp->height = height;

	vp->zoom = static_cast<ZoomLevel>(Clamp(zoom, _settings_client.gui.zoom_min, _settings_client.gui.zoom_max));

	vp->virtual_width = ScaleByZoom(width, zoom);
	vp->virtual_height = ScaleByZoom(height, zoom);

	Point pt;

	if (follow_flags & 0x80000000) {
		const Vehicle *veh;

		vp->follow_vehicle = (VehicleID)(follow_flags & 0xFFFFF);
		veh = Vehicle::Get(vp->follow_vehicle);
		pt = MapXYZToViewport(vp, veh->x_pos, veh->y_pos, veh->z_pos);
	} else {
		uint x = TileX(follow_flags) * TILE_SIZE;
		uint y = TileY(follow_flags) * TILE_SIZE;

		vp->follow_vehicle = INVALID_VEHICLE;
		pt = MapXYZToViewport(vp, x, y, GetSlopePixelZ(x, y));
	}

	vp->scrollpos_x = pt.x;
	vp->scrollpos_y = pt.y;
	vp->dest_scrollpos_x = pt.x;
	vp->dest_scrollpos_y = pt.y;

	vp->overlay = NULL;

	w->viewport = vp;
	vp->virtual_left = 0; // pt.x;
	vp->virtual_top = 0;  // pt.y;
}

static Point _vp_move_offs;

static void DoSetViewportPosition(const Window *w, int left, int top, int width, int height)
{
	FOR_ALL_WINDOWS_FROM_BACK_FROM(w, w) {
		if (left + width > w->left &&
				w->left + w->width > left &&
				top + height > w->top &&
				w->top + w->height > top) {

			if (left < w->left) {
				DoSetViewportPosition(w, left, top, w->left - left, height);
				DoSetViewportPosition(w, left + (w->left - left), top, width - (w->left - left), height);
				return;
			}

			if (left + width > w->left + w->width) {
				DoSetViewportPosition(w, left, top, (w->left + w->width - left), height);
				DoSetViewportPosition(w, left + (w->left + w->width - left), top, width - (w->left + w->width - left), height);
				return;
			}

			if (top < w->top) {
				DoSetViewportPosition(w, left, top, width, (w->top - top));
				DoSetViewportPosition(w, left, top + (w->top - top), width, height - (w->top - top));
				return;
			}

			if (top + height > w->top + w->height) {
				DoSetViewportPosition(w, left, top, width, (w->top + w->height - top));
				DoSetViewportPosition(w, left, top + (w->top + w->height - top), width, height - (w->top + w->height - top));
				return;
			}

			return;
		}
	}

	{
		int xo = _vp_move_offs.x;
		int yo = _vp_move_offs.y;

		if (abs(xo) >= width || abs(yo) >= height) {
			/* fully_outside */
			RedrawScreenRect(left, top, left + width, top + height);
			return;
		}

		GfxScroll(left, top, width, height, xo, yo);

		if (xo > 0) {
			RedrawScreenRect(left, top, xo + left, top + height);
			left += xo;
			width -= xo;
		} else if (xo < 0) {
			RedrawScreenRect(left + width + xo, top, left + width, top + height);
			width += xo;
		}

		if (yo > 0) {
			RedrawScreenRect(left, top, width + left, top + yo);
		} else if (yo < 0) {
			RedrawScreenRect(left, top + height + yo, width + left, top + height);
		}
	}
}

static void SetViewportPosition(Window *w, int x, int y)
{
	ViewPort *vp = w->viewport;
	int old_left = vp->virtual_left;
	int old_top = vp->virtual_top;
	int i;
	int left, top, width, height;

	vp->virtual_left = x;
	vp->virtual_top = y;

	/* Viewport is bound to its left top corner, so it must be rounded down (UnScaleByZoomLower)
	 * else glitch described in FS#1412 will happen (offset by 1 pixel with zoom level > NORMAL)
	 */
	old_left = UnScaleByZoomLower(old_left, vp->zoom);
	old_top = UnScaleByZoomLower(old_top, vp->zoom);
	x = UnScaleByZoomLower(x, vp->zoom);
	y = UnScaleByZoomLower(y, vp->zoom);

	old_left -= x;
	old_top -= y;

	if (old_top == 0 && old_left == 0) return;

	_vp_move_offs.x = old_left;
	_vp_move_offs.y = old_top;

	left = vp->left;
	top = vp->top;
	width = vp->width;
	height = vp->height;

	if (left < 0) {
		width += left;
		left = 0;
	}

	i = left + width - _screen.width;
	if (i >= 0) width -= i;

	if (width > 0) {
		if (top < 0) {
			height += top;
			top = 0;
		}

		i = top + height - _screen.height;
		if (i >= 0) height -= i;

		if (height > 0) DoSetViewportPosition(w->z_front, left, top, width, height);
	}
}

/**
 * Is a xy position inside the viewport of the window?
 * @param w Window to examine its viewport
 * @param x X coordinate of the xy position
 * @param y Y coordinate of the xy position
 * @return Pointer to the viewport if the xy position is in the viewport of the window,
 *         otherwise \c NULL is returned.
 */
ViewPort *IsPtInWindowViewport(const Window *w, int x, int y)
{
	ViewPort *vp = w->viewport;

	if (vp != NULL &&
			IsInsideMM(x, vp->left, vp->left + vp->width) &&
			IsInsideMM(y, vp->top, vp->top + vp->height))
		return vp;

	return NULL;
}

/**
 * Translate screen coordinate in a viewport to a tile coordinate
 * @param vp  Viewport that contains the (\a x, \a y) screen coordinate
 * @param x   Screen x coordinate
 * @param y   Screen y coordinate
 * @param clamp_to_map Clamp the coordinate outside of the map to the closest tile within the map.
 * @return Tile coordinate
 */
Point TranslateXYToTileCoord(const ViewPort *vp, int x, int y, bool clamp_to_map)
{
	Point pt;
	int a, b;
	int z;

	if ( (uint)(x -= vp->left) >= (uint)vp->width ||
				(uint)(y -= vp->top) >= (uint)vp->height) {
				Point pt = {-1, -1};
				return pt;
	}

	x = (ScaleByZoom(x, vp->zoom) + vp->virtual_left) >> (2 + ZOOM_LVL_SHIFT);
	y = (ScaleByZoom(y, vp->zoom) + vp->virtual_top) >> (1 + ZOOM_LVL_SHIFT);

	a = y - x;
	b = y + x;

	if (clamp_to_map) {
		/* Bring the coordinates near to a valid range. This is mostly due to the
		 * tiles on the north side of the map possibly being drawn too high due to
		 * the extra height levels. So at the top we allow a number of extra tiles.
		 * This number is based on the tile height and pixels. */
		int extra_tiles = CeilDiv(_settings_game.construction.max_heightlevel * TILE_HEIGHT, TILE_PIXELS);
		a = Clamp(a, -extra_tiles * TILE_SIZE, MapMaxX() * TILE_SIZE - 1);
		b = Clamp(b, -extra_tiles * TILE_SIZE, MapMaxY() * TILE_SIZE - 1);
	}

	/* (a, b) is the X/Y-world coordinate that belongs to (x,y) if the landscape would be completely flat on height 0.
	 * Now find the Z-world coordinate by fix point iteration.
	 * This is a bit tricky because the tile height is non-continuous at foundations.
	 * The clicked point should be approached from the back, otherwise there are regions that are not clickable.
	 * (FOUNDATION_HALFTILE_LOWER on SLOPE_STEEP_S hides north halftile completely)
	 * So give it a z-malus of 4 in the first iterations.
	 */
	z = 0;

	int min_coord = _settings_game.construction.freeform_edges ? TILE_SIZE : 0;

	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(a + max(z, 4) - 4, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + max(z, 4) - 4, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
	for (int malus = 3; malus > 0; malus--) z = GetSlopePixelZ(Clamp(a + max(z, malus) - malus, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + max(z, malus) - malus, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(a + z, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + z, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;

	if (clamp_to_map) {
		pt.x = Clamp(a + z, min_coord, MapMaxX() * TILE_SIZE - 1);
		pt.y = Clamp(b + z, min_coord, MapMaxY() * TILE_SIZE - 1);
	} else {
		pt.x = a + z;
		pt.y = b + z;
	}

	return pt;
}

/* When used for zooming, check area below current coordinates (x,y)
 * and return the tile of the zoomed out/in position (zoom_x, zoom_y)
 * when you just want the tile, make x = zoom_x and y = zoom_y */
static Point GetTileFromScreenXY(int x, int y, int zoom_x, int zoom_y)
{
	Window *w;
	ViewPort *vp;
	Point pt;

	if ( (w = FindWindowFromPt(x, y)) != NULL &&
			 (vp = IsPtInWindowViewport(w, x, y)) != NULL)
				return TranslateXYToTileCoord(vp, zoom_x, zoom_y);

	pt.y = pt.x = -1;
	return pt;
}

Point GetTileBelowCursor()
{
	return GetTileFromScreenXY(_cursor.pos.x, _cursor.pos.y, _cursor.pos.x, _cursor.pos.y);
}


Point GetTileZoomCenterWindow(bool in, Window * w)
{
	int x, y;
	ViewPort *vp = w->viewport;

	if (in) {
		x = ((_cursor.pos.x - vp->left) >> 1) + (vp->width >> 2);
		y = ((_cursor.pos.y - vp->top) >> 1) + (vp->height >> 2);
	} else {
		x = vp->width - (_cursor.pos.x - vp->left);
		y = vp->height - (_cursor.pos.y - vp->top);
	}
	/* Get the tile below the cursor and center on the zoomed-out center */
	return GetTileFromScreenXY(_cursor.pos.x, _cursor.pos.y, x + vp->left, y + vp->top);
}

/**
 * Update the status of the zoom-buttons according to the zoom-level
 * of the viewport. This will update their status and invalidate accordingly
 * @param w Window pointer to the window that has the zoom buttons
 * @param vp pointer to the viewport whose zoom-level the buttons represent
 * @param widget_zoom_in widget index for window with zoom-in button
 * @param widget_zoom_out widget index for window with zoom-out button
 */
void HandleZoomMessage(Window *w, const ViewPort *vp, byte widget_zoom_in, byte widget_zoom_out)
{
	w->SetWidgetDisabledState(widget_zoom_in, vp->zoom <= _settings_client.gui.zoom_min);
	w->SetWidgetDirty(widget_zoom_in);

	w->SetWidgetDisabledState(widget_zoom_out, vp->zoom >= _settings_client.gui.zoom_max);
	w->SetWidgetDirty(widget_zoom_out);
}

/**
 * Schedules a tile sprite for drawing.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x position x (world coordinates) of the sprite.
 * @param y position y (world coordinates) of the sprite.
 * @param z position z (world coordinates) of the sprite.
 * @param sub Only draw a part of the sprite.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
static void AddTileSpriteToDraw(SpriteID image, PaletteID pal, int32 x, int32 y, int z, const SubSprite *sub = NULL, int extra_offs_x = 0, int extra_offs_y = 0)
{
	assert((image & SPRITE_MASK) < MAX_SPRITES);

	TileSpriteToDraw *ts = _vd.tile_sprites_to_draw.Append();
	ts->image = image;
	ts->pal = pal;
	ts->sub = sub;
	Point pt = RemapCoords(x, y, z);
	ts->x = pt.x + extra_offs_x;
	ts->y = pt.y + extra_offs_y;
}

/**
 * Adds a child sprite to the active foundation.
 *
 * The pixel offset of the sprite relative to the ParentSprite is the sum of the offset passed to OffsetGroundSprite() and extra_offs_?.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param sub Only draw a part of the sprite.
 * @param foundation_part Foundation part.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
static void AddChildSpriteToFoundation(SpriteID image, PaletteID pal, const SubSprite *sub, FoundationPart foundation_part, int extra_offs_x, int extra_offs_y)
{
	assert(IsInsideMM(foundation_part, 0, FOUNDATION_PART_END));
	assert(_vd.foundation[foundation_part] != -1);
	Point offs = _vd.foundation_offset[foundation_part];

	/* Change the active ChildSprite list to the one of the foundation */
	int *old_child = _vd.last_child;
	_vd.last_child = _vd.last_foundation_child[foundation_part];

	AddChildSpriteScreen(image, pal, offs.x + extra_offs_x, offs.y + extra_offs_y, false, sub, false);

	/* Switch back to last ChildSprite list */
	_vd.last_child = old_child;
}

/**
 * Draws a ground sprite at a specific world-coordinate relative to the current tile.
 * If the current tile is drawn on top of a foundation the sprite is added as child sprite to the "foundation"-ParentSprite.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x position x (world coordinates) of the sprite relative to current tile.
 * @param y position y (world coordinates) of the sprite relative to current tile.
 * @param z position z (world coordinates) of the sprite relative to current tile.
 * @param sub Only draw a part of the sprite.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
void DrawGroundSpriteAt(SpriteID image, PaletteID pal, int32 x, int32 y, int z, const SubSprite *sub, int extra_offs_x, int extra_offs_y)
{
	/* Switch to first foundation part, if no foundation was drawn */
	if (_vd.foundation_part == FOUNDATION_PART_NONE) _vd.foundation_part = FOUNDATION_PART_NORMAL;

	if (_vd.foundation[_vd.foundation_part] != -1) {
		Point pt = RemapCoords(x, y, z);
		AddChildSpriteToFoundation(image, pal, sub, _vd.foundation_part, pt.x + extra_offs_x * ZOOM_LVL_BASE, pt.y + extra_offs_y * ZOOM_LVL_BASE);
	} else {
		AddTileSpriteToDraw(image, pal, _cur_ti->x + x, _cur_ti->y + y, _cur_ti->z + z, sub, extra_offs_x * ZOOM_LVL_BASE, extra_offs_y * ZOOM_LVL_BASE);
	}
}

/**
 * Draws a ground sprite for the current tile.
 * If the current tile is drawn on top of a foundation the sprite is added as child sprite to the "foundation"-ParentSprite.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param sub Only draw a part of the sprite.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
void DrawGroundSprite(SpriteID image, PaletteID pal, const SubSprite *sub, int extra_offs_x, int extra_offs_y)
{
	DrawGroundSpriteAt(image, pal, 0, 0, 0, sub, extra_offs_x, extra_offs_y);
}

/**
 * Called when a foundation has been drawn for the current tile.
 * Successive ground sprites for the current tile will be drawn as child sprites of the "foundation"-ParentSprite, not as TileSprites.
 *
 * @param x sprite x-offset (screen coordinates) of ground sprites relative to the "foundation"-ParentSprite.
 * @param y sprite y-offset (screen coordinates) of ground sprites relative to the "foundation"-ParentSprite.
 */
void OffsetGroundSprite(int x, int y)
{
	/* Switch to next foundation part */
	switch (_vd.foundation_part) {
		case FOUNDATION_PART_NONE:
			_vd.foundation_part = FOUNDATION_PART_NORMAL;
			break;
		case FOUNDATION_PART_NORMAL:
			_vd.foundation_part = FOUNDATION_PART_HALFTILE;
			break;
		default: NOT_REACHED();
	}

	/* _vd.last_child == NULL if foundation sprite was clipped by the viewport bounds */
	if (_vd.last_child != NULL) _vd.foundation[_vd.foundation_part] = _vd.parent_sprites_to_draw.Length() - 1;

	_vd.foundation_offset[_vd.foundation_part].x = x * ZOOM_LVL_BASE;
	_vd.foundation_offset[_vd.foundation_part].y = y * ZOOM_LVL_BASE;
	_vd.last_foundation_child[_vd.foundation_part] = _vd.last_child;
}

/**
 * Adds a child sprite to a parent sprite.
 * In contrast to "AddChildSpriteScreen()" the sprite position is in world coordinates
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x position x of the sprite.
 * @param y position y of the sprite.
 * @param z position z of the sprite.
 * @param sub Only draw a part of the sprite.
 */
static void AddCombinedSprite(SpriteID image, PaletteID pal, int x, int y, int z, const SubSprite *sub)
{
	Point pt = RemapCoords(x, y, z);
	const Sprite *spr = GetSprite(image & SPRITE_MASK, ST_NORMAL);

	if (pt.x + spr->x_offs >= _vd.dpi.left + _vd.dpi.width ||
			pt.x + spr->x_offs + spr->width <= _vd.dpi.left ||
			pt.y + spr->y_offs >= _vd.dpi.top + _vd.dpi.height ||
			pt.y + spr->y_offs + spr->height <= _vd.dpi.top)
		return;

	const ParentSpriteToDraw *pstd = _vd.parent_sprites_to_draw.End() - 1;
	AddChildSpriteScreen(image, pal, pt.x - pstd->left, pt.y - pstd->top, false, sub, false);
}

/**
 * Draw a (transparent) sprite at given coordinates with a given bounding box.
 * The bounding box extends from (x + bb_offset_x, y + bb_offset_y, z + bb_offset_z) to (x + w - 1, y + h - 1, z + dz - 1), both corners included.
 * Bounding boxes with bb_offset_x == w or bb_offset_y == h or bb_offset_z == dz are allowed and produce thin slices.
 *
 * @note Bounding boxes are normally specified with bb_offset_x = bb_offset_y = bb_offset_z = 0. The extent of the bounding box in negative direction is
 *       defined by the sprite offset in the grf file.
 *       However if modifying the sprite offsets is not suitable (e.g. when using existing graphics), the bounding box can be tuned by bb_offset.
 *
 * @pre w >= bb_offset_x, h >= bb_offset_y, dz >= bb_offset_z. Else w, h or dz are ignored.
 *
 * @param image the image to combine and draw,
 * @param pal the provided palette,
 * @param x position X (world) of the sprite,
 * @param y position Y (world) of the sprite,
 * @param w bounding box extent towards positive X (world),
 * @param h bounding box extent towards positive Y (world),
 * @param dz bounding box extent towards positive Z (world),
 * @param z position Z (world) of the sprite,
 * @param transparent if true, switch the palette between the provided palette and the transparent palette,
 * @param bb_offset_x bounding box extent towards negative X (world),
 * @param bb_offset_y bounding box extent towards negative Y (world),
 * @param bb_offset_z bounding box extent towards negative Z (world)
 * @param sub Only draw a part of the sprite.
 */
void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w, int h, int dz, int z, bool transparent, int bb_offset_x, int bb_offset_y, int bb_offset_z, const SubSprite *sub)
{
	int32 left, right, top, bottom;

	assert((image & SPRITE_MASK) < MAX_SPRITES);

	/* make the sprites transparent with the right palette */
	if (transparent) {
		SetBit(image, PALETTE_MODIFIER_TRANSPARENT);
		pal = PALETTE_TO_TRANSPARENT;
	}

	if (_vd.combine_sprites == SPRITE_COMBINE_ACTIVE) {
		AddCombinedSprite(image, pal, x, y, z, sub);
		return;
	}

	_vd.last_child = NULL;

	Point pt = RemapCoords(x, y, z);
	int tmp_left, tmp_top, tmp_x = pt.x, tmp_y = pt.y;

	/* Compute screen extents of sprite */
	if (image == SPR_EMPTY_BOUNDING_BOX) {
		left = tmp_left = RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x;
		right           = RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x + 1;
		top  = tmp_top  = RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y;
		bottom          = RemapCoords(x + w          , y + h          , z + bb_offset_z).y + 1;
	} else {
		const Sprite *spr = GetSprite(image & SPRITE_MASK, ST_NORMAL);
		left = tmp_left = (pt.x += spr->x_offs);
		right           = (pt.x +  spr->width );
		top  = tmp_top  = (pt.y += spr->y_offs);
		bottom          = (pt.y +  spr->height);
	}

	if (_draw_bounding_boxes && (image != SPR_EMPTY_BOUNDING_BOX)) {
		/* Compute maximal extents of sprite and its bounding box */
		left   = min(left  , RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x);
		right  = max(right , RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x + 1);
		top    = min(top   , RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y);
		bottom = max(bottom, RemapCoords(x + w          , y + h          , z + bb_offset_z).y + 1);
	}

	/* Do not add the sprite to the viewport, if it is outside */
	if (left   >= _vd.dpi.left + _vd.dpi.width ||
	    right  <= _vd.dpi.left                 ||
	    top    >= _vd.dpi.top + _vd.dpi.height ||
	    bottom <= _vd.dpi.top) {
		return;
	}

	ParentSpriteToDraw *ps = _vd.parent_sprites_to_draw.Append();
	ps->x = tmp_x;
	ps->y = tmp_y;

	ps->left = tmp_left;
	ps->top  = tmp_top;

	ps->image = image;
	ps->pal = pal;
	ps->sub = sub;
	ps->xmin = x + bb_offset_x;
	ps->xmax = x + max(bb_offset_x, w) - 1;

	ps->ymin = y + bb_offset_y;
	ps->ymax = y + max(bb_offset_y, h) - 1;

	ps->zmin = z + bb_offset_z;
	ps->zmax = z + max(bb_offset_z, dz) - 1;

	ps->comparison_done = false;
	ps->first_child = -1;

	_vd.last_child = &ps->first_child;

	if (_vd.combine_sprites == SPRITE_COMBINE_PENDING) _vd.combine_sprites = SPRITE_COMBINE_ACTIVE;
}

/**
 * Starts a block of sprites, which are "combined" into a single bounding box.
 *
 * Subsequent calls to #AddSortableSpriteToDraw will be drawn into the same bounding box.
 * That is: The first sprite that is not clipped by the viewport defines the bounding box, and
 * the following sprites will be child sprites to that one.
 *
 * That implies:
 *  - The drawing order is definite. No other sprites will be sorted between those of the block.
 *  - You have to provide a valid bounding box for all sprites,
 *    as you won't know which one is the first non-clipped one.
 *    Preferable you use the same bounding box for all.
 *  - You cannot use #AddChildSpriteScreen inside the block, as its result will be indefinite.
 *
 * The block is terminated by #EndSpriteCombine.
 *
 * You cannot nest "combined" blocks.
 */
void StartSpriteCombine()
{
	assert(_vd.combine_sprites == SPRITE_COMBINE_NONE);
	_vd.combine_sprites = SPRITE_COMBINE_PENDING;
}

/**
 * Terminates a block of sprites started by #StartSpriteCombine.
 * Take a look there for details.
 */
void EndSpriteCombine()
{
	assert(_vd.combine_sprites != SPRITE_COMBINE_NONE);
	_vd.combine_sprites = SPRITE_COMBINE_NONE;
}

/**
 * Check if the parameter "check" is inside the interval between
 * begin and end, including both begin and end.
 * @note Whether \c begin or \c end is the biggest does not matter.
 *       This method will account for that.
 * @param begin The begin of the interval.
 * @param end   The end of the interval.
 * @param check The value to check.
 */
static bool IsInRangeInclusive(int begin, int end, int check)
{
	if (begin > end) Swap(begin, end);
	return begin <= check && check <= end;
}

/**
 * Checks whether a point is inside the selected a diagonal rectangle given by _thd.size and _thd.pos
 * @param x The x coordinate of the point to be checked.
 * @param y The y coordinate of the point to be checked.
 * @return True if the point is inside the rectangle, else false.
 */
bool IsInsideRotatedRectangle(int x, int y)
{
	int dist_a = (_thd.size.x + _thd.size.y);      // Rotated coordinate system for selected rectangle.
	int dist_b = (_thd.size.x - _thd.size.y);      // We don't have to divide by 2. It's all relative!
	int a = ((x - _thd.pos.x) + (y - _thd.pos.y)); // Rotated coordinate system for the point under scrutiny.
	int b = ((x - _thd.pos.x) - (y - _thd.pos.y));

	/* Check if a and b are between 0 and dist_a or dist_b respectively. */
	return IsInRangeInclusive(dist_a, 0, a) && IsInRangeInclusive(dist_b, 0, b);
}

/**
 * Add a child sprite to a parent sprite.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x sprite x-offset (screen coordinates) relative to parent sprite.
 * @param y sprite y-offset (screen coordinates) relative to parent sprite.
 * @param transparent if true, switch the palette between the provided palette and the transparent palette,
 * @param sub Only draw a part of the sprite.
 */
void AddChildSpriteScreen(SpriteID image, PaletteID pal, int x, int y, bool transparent, const SubSprite *sub, bool scale)
{
	assert((image & SPRITE_MASK) < MAX_SPRITES);

	/* If the ParentSprite was clipped by the viewport bounds, do not draw the ChildSprites either */
	if (_vd.last_child == NULL) return;

	/* make the sprites transparent with the right palette */
	if (transparent) {
		SetBit(image, PALETTE_MODIFIER_TRANSPARENT);
		pal = PALETTE_TO_TRANSPARENT;
	}

	*_vd.last_child = _vd.child_screen_sprites_to_draw.Length();

	ChildScreenSpriteToDraw *cs = _vd.child_screen_sprites_to_draw.Append();
	cs->image = image;
	cs->pal = pal;
	cs->sub = sub;
	cs->x = scale ? x * ZOOM_LVL_BASE : x;
	cs->y = scale ? y * ZOOM_LVL_BASE : y;
	cs->next = -1;

	/* Append the sprite to the active ChildSprite list.
	 * If the active ParentSprite is a foundation, update last_foundation_child as well.
	 * Note: ChildSprites of foundations are NOT sequential in the vector, as selection sprites are added at last. */
	if (_vd.last_foundation_child[0] == _vd.last_child) _vd.last_foundation_child[0] = &cs->next;
	if (_vd.last_foundation_child[1] == _vd.last_child) _vd.last_foundation_child[1] = &cs->next;
	_vd.last_child = &cs->next;
}

static void AddStringToDraw(int x, int y, StringID string, uint64 params_1, uint64 params_2, Colours colour, uint16 width)
{
	assert(width != 0);
	StringSpriteToDraw *ss = _vd.string_sprites_to_draw.Append();
	ss->string = string;
	ss->x = x;
	ss->y = y;
	ss->params[0] = params_1;
	ss->params[1] = params_2;
	ss->width = width;
	ss->colour = colour;
}


/**
 * Draws sprites between ground sprite and everything above.
 *
 * The sprite is either drawn as TileSprite or as ChildSprite of the active foundation.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param ti TileInfo Tile that is being drawn
 * @param z_offset Z offset relative to the groundsprite. Only used for the sprite position, not for sprite sorting.
 * @param foundation_part Foundation part the sprite belongs to.
 */
static void DrawSelectionSprite(SpriteID image, PaletteID pal, const TileInfo *ti, int z_offset, FoundationPart foundation_part)
{
	/* FIXME: This is not totally valid for some autorail highlights that extend over the edges of the tile. */
	if (_vd.foundation[foundation_part] == -1) {
		/* draw on real ground */
		AddTileSpriteToDraw(image, pal, ti->x, ti->y, ti->z + z_offset);
	} else {
		/* draw on top of foundation */
		AddChildSpriteToFoundation(image, pal, NULL, foundation_part, 0, -z_offset * ZOOM_LVL_BASE);
	}
}

/**
 * Draws a selection rectangle on a tile.
 *
 * @param ti TileInfo Tile that is being drawn
 * @param pal Palette to apply.
 */
static void DrawTileSelectionRect(const TileInfo *ti, PaletteID pal)
{
	if (!IsValidTile(ti->tile)) return;

	SpriteID sel;
	if (IsHalftileSlope(ti->tileh)) {
		Corner halftile_corner = GetHalftileSlopeCorner(ti->tileh);
		SpriteID sel2 = SPR_HALFTILE_SELECTION_FLAT + halftile_corner;
		DrawSelectionSprite(sel2, pal, ti, 7 + TILE_HEIGHT, FOUNDATION_PART_HALFTILE);

		Corner opposite_corner = OppositeCorner(halftile_corner);
		if (IsSteepSlope(ti->tileh)) {
			sel = SPR_HALFTILE_SELECTION_DOWN;
		} else {
			sel = ((ti->tileh & SlopeWithOneCornerRaised(opposite_corner)) != 0 ? SPR_HALFTILE_SELECTION_UP : SPR_HALFTILE_SELECTION_FLAT);
		}
		sel += opposite_corner;
	} else {
		sel = SPR_SELECT_TILE + SlopeToSpriteOffset(ti->tileh);
	}
	DrawSelectionSprite(sel, pal, ti, 7, FOUNDATION_PART_NORMAL);
}

static bool IsPartOfAutoLine(int px, int py)
{
	px -= _thd.selstart.x;
	py -= _thd.selstart.y;

	if ((_thd.drawstyle & HT_DRAG_MASK) != HT_LINE) return false;

	switch (_thd.drawstyle & HT_DIR_MASK) {
		case HT_DIR_X:  return py == 0; // x direction
		case HT_DIR_Y:  return px == 0; // y direction
		case HT_DIR_HU: return px == -py || px == -py - 16; // horizontal upper
		case HT_DIR_HL: return px == -py || px == -py + 16; // horizontal lower
		case HT_DIR_VL: return px == py || px == py + 16; // vertical left
		case HT_DIR_VR: return px == py || px == py - 16; // vertical right
		default:
			NOT_REACHED();
	}
}

/* [direction][side] */
static const HighLightStyle _autorail_type[6][2] = {
	{ HT_DIR_X,  HT_DIR_X },
	{ HT_DIR_Y,  HT_DIR_Y },
	{ HT_DIR_HU, HT_DIR_HL },
	{ HT_DIR_HL, HT_DIR_HU },
	{ HT_DIR_VL, HT_DIR_VR },
	{ HT_DIR_VR, HT_DIR_VL }
};

#include "table/autorail.h"

/**
 * Draws autorail highlights.
 *
 * @param *ti TileInfo Tile that is being drawn
 * @param autorail_type Offset into _AutorailTilehSprite[][]
 */
static void DrawAutorailSelection(const TileInfo *ti, uint autorail_type)
{
	SpriteID image;
	PaletteID pal;
	int offset;

	FoundationPart foundation_part = FOUNDATION_PART_NORMAL;
	Slope autorail_tileh = RemoveHalftileSlope(ti->tileh);
	if (IsHalftileSlope(ti->tileh)) {
		static const uint _lower_rail[4] = { 5U, 2U, 4U, 3U };
		Corner halftile_corner = GetHalftileSlopeCorner(ti->tileh);
		if (autorail_type != _lower_rail[halftile_corner]) {
			foundation_part = FOUNDATION_PART_HALFTILE;
			/* Here we draw the highlights of the "three-corners-raised"-slope. That looks ok to me. */
			autorail_tileh = SlopeWithThreeCornersRaised(OppositeCorner(halftile_corner));
		}
	}

	offset = _AutorailTilehSprite[autorail_tileh][autorail_type];
	if (offset >= 0) {
		image = SPR_AUTORAIL_BASE + offset;
		pal = PAL_NONE;
	} else {
		image = SPR_AUTORAIL_BASE - offset;
		pal = PALETTE_SEL_TILE_RED;
	}

	DrawSelectionSprite(image, _thd.make_square_red ? PALETTE_SEL_TILE_RED : pal, ti, 7, foundation_part);
}

/**
 * Checks if the specified tile is selected and if so draws selection using correct selectionstyle.
 * @param *ti TileInfo Tile that is being drawn
 */
static void DrawTileSelection(const TileInfo *ti)
{
	/* Draw a red error square? */
	bool is_redsq = _thd.redsq == ti->tile;
	if (is_redsq) DrawTileSelectionRect(ti, PALETTE_TILE_RED_PULSATING);

	/* No tile selection active? */
	if ((_thd.drawstyle & HT_DRAG_MASK) == HT_NONE) return;

	if (_thd.diagonal) { // We're drawing a 45 degrees rotated (diagonal) rectangle
		if (IsInsideRotatedRectangle((int)ti->x, (int)ti->y)) goto draw_inner;
		return;
	}

	/* Inside the inner area? */
	if (IsInsideBS(ti->x, _thd.pos.x, _thd.size.x) &&
			IsInsideBS(ti->y, _thd.pos.y, _thd.size.y)) {
draw_inner:
		if (_thd.drawstyle & HT_RECT) {
			if (!is_redsq) DrawTileSelectionRect(ti, _thd.make_square_red ? PALETTE_SEL_TILE_RED : PAL_NONE);
		} else if (_thd.drawstyle & HT_POINT) {
			/* Figure out the Z coordinate for the single dot. */
			int z = 0;
			FoundationPart foundation_part = FOUNDATION_PART_NORMAL;
			if (ti->tileh & SLOPE_N) {
				z += TILE_HEIGHT;
				if (RemoveHalftileSlope(ti->tileh) == SLOPE_STEEP_N) z += TILE_HEIGHT;
			}
			if (IsHalftileSlope(ti->tileh)) {
				Corner halftile_corner = GetHalftileSlopeCorner(ti->tileh);
				if ((halftile_corner == CORNER_W) || (halftile_corner == CORNER_E)) z += TILE_HEIGHT;
				if (halftile_corner != CORNER_S) {
					foundation_part = FOUNDATION_PART_HALFTILE;
					if (IsSteepSlope(ti->tileh)) z -= TILE_HEIGHT;
				}
			}
			DrawSelectionSprite(_cur_dpi->zoom <= ZOOM_LVL_DETAIL ? SPR_DOT : SPR_DOT_SMALL, PAL_NONE, ti, z, foundation_part);
		} else if (_thd.drawstyle & HT_RAIL) {
			/* autorail highlight piece under cursor */
			HighLightStyle type = _thd.drawstyle & HT_DIR_MASK;
			assert(type < HT_DIR_END);
			DrawAutorailSelection(ti, _autorail_type[type][0]);
		} else if (IsPartOfAutoLine(ti->x, ti->y)) {
			/* autorail highlighting long line */
			HighLightStyle dir = _thd.drawstyle & HT_DIR_MASK;
			uint side;

			if (dir == HT_DIR_X || dir == HT_DIR_Y) {
				side = 0;
			} else {
				TileIndex start = TileVirtXY(_thd.selstart.x, _thd.selstart.y);
				side = Delta(Delta(TileX(start), TileX(ti->tile)), Delta(TileY(start), TileY(ti->tile)));
			}

			DrawAutorailSelection(ti, _autorail_type[dir][side]);
		}
		return;
	}

	/* Check if it's inside the outer area? */
	if (!is_redsq && _thd.outersize.x > 0 &&
			IsInsideBS(ti->x, _thd.pos.x + _thd.offs.x, _thd.size.x + _thd.outersize.x) &&
			IsInsideBS(ti->y, _thd.pos.y + _thd.offs.y, _thd.size.y + _thd.outersize.y)) {
		/* Draw a blue rect. */
		DrawTileSelectionRect(ti, PALETTE_SEL_TILE_BLUE);
		return;
	}
}

/**
 * Returns the y coordinate in the viewport coordinate system where the given
 * tile is painted.
 * @param tile Any tile.
 * @return The viewport y coordinate where the tile is painted.
 */
static int GetViewportY(Point tile)
{
	/* Each increment in X or Y direction moves down by half a tile, i.e. TILE_PIXELS / 2. */
	return (tile.y * (int)(TILE_PIXELS / 2) + tile.x * (int)(TILE_PIXELS / 2) - TilePixelHeightOutsideMap(tile.x, tile.y)) << ZOOM_LVL_SHIFT;
}

/**
 * Add the landscape to the viewport, i.e. all ground tiles and buildings.
 */
static void ViewportAddLandscape()
{
	assert(_vd.dpi.top <= _vd.dpi.top + _vd.dpi.height);
	assert(_vd.dpi.left <= _vd.dpi.left + _vd.dpi.width);

	Point upper_left = InverseRemapCoords(_vd.dpi.left, _vd.dpi.top);
	Point upper_right = InverseRemapCoords(_vd.dpi.left + _vd.dpi.width, _vd.dpi.top);

	/* Transformations between tile coordinates and viewport rows/columns: See vp_column_row
	 *   column = y - x
	 *   row    = x + y
	 *   x      = (row - column) / 2
	 *   y      = (row + column) / 2
	 * Note: (row, columns) pairs are only valid, if they are both even or both odd.
	 */

	/* Columns overlap with neighbouring columns by a half tile.
	 *  - Left column is column of upper_left (rounded down) and one column to the left.
	 *  - Right column is column of upper_right (rounded up) and one column to the right.
	 * Note: Integer-division does not round down for negative numbers, so ensure rounding with another increment/decrement.
	 */
	int left_column = (upper_left.y - upper_left.x) / (int)TILE_SIZE - 2;
	int right_column = (upper_right.y - upper_right.x) / (int)TILE_SIZE + 2;

	int potential_bridge_height = ZOOM_LVL_BASE * TILE_HEIGHT * _settings_game.construction.max_bridge_height;

	/* Rows overlap with neighbouring rows by a half tile.
	 * The first row that could possibly be visible is the row above upper_left (if it is at height 0).
	 * Due to integer-division not rounding down for negative numbers, we need another decrement.
	 */
	int row = (upper_left.x + upper_left.y) / (int)TILE_SIZE - 2;
	bool last_row = false;
	for (; !last_row; row++) {
		last_row = true;
		for (int column = left_column; column <= right_column; column++) {
			/* Valid row/column? */
			if ((row + column) % 2 != 0) continue;

			Point tilecoord;
			tilecoord.x = (row - column) / 2;
			tilecoord.y = (row + column) / 2;
			assert(column == tilecoord.y - tilecoord.x);
			assert(row == tilecoord.y + tilecoord.x);

			TileType tile_type;
			TileInfo tile_info;
			_cur_ti = &tile_info;
			tile_info.x = tilecoord.x * TILE_SIZE; // FIXME tile_info should use signed integers
			tile_info.y = tilecoord.y * TILE_SIZE;

			if (IsInsideBS(tilecoord.x, 0, MapSizeX()) && IsInsideBS(tilecoord.y, 0, MapSizeY())) {
				/* This includes the south border at MapMaxX / MapMaxY. When terraforming we still draw tile selections there. */
				tile_info.tile = TileXY(tilecoord.x, tilecoord.y);
				tile_type = GetTileType(tile_info.tile);
			} else {
				tile_info.tile = INVALID_TILE;
				tile_type = MP_VOID;
			}

			if (tile_type != MP_VOID) {
				/* We are inside the map => paint landscape. */
				tile_info.tileh = GetTilePixelSlope(tile_info.tile, &tile_info.z);
			} else {
				/* We are outside the map => paint black. */
				tile_info.tileh = GetTilePixelSlopeOutsideMap(tilecoord.x, tilecoord.y, &tile_info.z);
			}

			int viewport_y = GetViewportY(tilecoord);

			if (viewport_y + MAX_TILE_EXTENT_BOTTOM < _vd.dpi.top) {
				/* The tile in this column is not visible yet.
				 * Tiles in other columns may be visible, but we need more rows in any case. */
				last_row = false;
				continue;
			}

			int min_visible_height = viewport_y - (_vd.dpi.top + _vd.dpi.height);
			bool tile_visible = min_visible_height <= 0;

			if (tile_type != MP_VOID) {
				/* Is tile with buildings visible? */
				if (min_visible_height < MAX_TILE_EXTENT_TOP) tile_visible = true;

				if (IsBridgeAbove(tile_info.tile)) {
					/* Is the bridge visible? */
					TileIndex bridge_tile = GetNorthernBridgeEnd(tile_info.tile);
					int bridge_height = ZOOM_LVL_BASE * (GetBridgePixelHeight(bridge_tile) - TilePixelHeight(tile_info.tile));
					if (min_visible_height < bridge_height + MAX_TILE_EXTENT_TOP) tile_visible = true;
				}

				/* Would a higher bridge on a more southern tile be visible?
				 * If yes, we need to loop over more rows to possibly find one. */
				if (min_visible_height < potential_bridge_height + MAX_TILE_EXTENT_TOP) last_row = false;
			} else {
				/* Outside of map. If we are on the north border of the map, there may still be a bridge visible,
				 * so we need to loop over more rows to possibly find one. */
				if ((tilecoord.x <= 0 || tilecoord.y <= 0) && min_visible_height < potential_bridge_height + MAX_TILE_EXTENT_TOP) last_row = false;
			}

			if (tile_visible) {
				last_row = false;
				_vd.foundation_part = FOUNDATION_PART_NONE;
				_vd.foundation[0] = -1;
				_vd.foundation[1] = -1;
				_vd.last_foundation_child[0] = NULL;
				_vd.last_foundation_child[1] = NULL;

				_tile_type_procs[tile_type]->draw_tile_proc(&tile_info);
				if (tile_info.tile != INVALID_TILE) DrawTileSelection(&tile_info);
			}
		}
	}
}

/**
 * Add a string to draw in the viewport
 * @param dpi current viewport area
 * @param small_from Zoomlevel from when the small font should be used
 * @param sign sign position and dimension
 * @param string_normal String for normal and 2x zoom level
 * @param string_small String for 4x and 8x zoom level
 * @param string_small_shadow Shadow string for 4x and 8x zoom level; or #STR_NULL if no shadow
 * @param colour colour of the sign background; or INVALID_COLOUR if transparent
 */
void ViewportAddString(const DrawPixelInfo *dpi, ZoomLevel small_from, const ViewportSign *sign, StringID string_normal, StringID string_small, StringID string_small_shadow, uint64 params_1, uint64 params_2, Colours colour)
{
	bool small = dpi->zoom >= small_from;

	int left   = dpi->left;
	int top    = dpi->top;
	int right  = left + dpi->width;
	int bottom = top + dpi->height;

	int sign_height     = ScaleByZoom(VPSM_TOP + FONT_HEIGHT_NORMAL + VPSM_BOTTOM, dpi->zoom);
	int sign_half_width = ScaleByZoom((small ? sign->width_small : sign->width_normal) / 2, dpi->zoom);

	if (bottom < sign->top ||
			top   > sign->top + sign_height ||
			right < sign->center - sign_half_width ||
			left  > sign->center + sign_half_width) {
		return;
	}

	if (!small) {
		AddStringToDraw(sign->center - sign_half_width, sign->top, string_normal, params_1, params_2, colour, sign->width_normal);
	} else {
		int shadow_offset = 0;
		if (string_small_shadow != STR_NULL) {
			shadow_offset = 4;
			AddStringToDraw(sign->center - sign_half_width + shadow_offset, sign->top, string_small_shadow, params_1, params_2, INVALID_COLOUR, sign->width_small);
		}
		AddStringToDraw(sign->center - sign_half_width, sign->top - shadow_offset, string_small, params_1, params_2,
				colour, sign->width_small | 0x8000);
	}
}

static void ViewportAddTownNames(DrawPixelInfo *dpi)
{
	if (!HasBit(_display_opt, DO_SHOW_TOWN_NAMES) || _game_mode == GM_MENU) return;

	const Town *t;
	FOR_ALL_TOWNS(t) {
		ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &t->cache.sign,
				_settings_client.gui.population_in_label ? STR_VIEWPORT_TOWN_POP : STR_VIEWPORT_TOWN,
				STR_VIEWPORT_TOWN_TINY_WHITE, STR_VIEWPORT_TOWN_TINY_BLACK,
				t->index, t->cache.population);
	}
}


static void ViewportAddStationNames(DrawPixelInfo *dpi)
{
	if (!(HasBit(_display_opt, DO_SHOW_STATION_NAMES) || HasBit(_display_opt, DO_SHOW_WAYPOINT_NAMES)) || _game_mode == GM_MENU) return;

	const BaseStation *st;
	FOR_ALL_BASE_STATIONS(st) {
		/* Check whether the base station is a station or a waypoint */
		bool is_station = Station::IsExpected(st);

		/* Don't draw if the display options are disabled */
		if (!HasBit(_display_opt, is_station ? DO_SHOW_STATION_NAMES : DO_SHOW_WAYPOINT_NAMES)) continue;

		/* Don't draw if station is owned by another company and competitor station names are hidden. Stations owned by none are never ignored. */
		if (!HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) && _local_company != st->owner && st->owner != OWNER_NONE) continue;

		ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &st->sign,
				is_station ? STR_VIEWPORT_STATION : STR_VIEWPORT_WAYPOINT,
				(is_station ? STR_VIEWPORT_STATION : STR_VIEWPORT_WAYPOINT) + 1, STR_NULL,
				st->index, st->facilities, (st->owner == OWNER_NONE || !st->IsInUse()) ? COLOUR_GREY : _company_colours[st->owner]);
	}
}


static void ViewportAddSigns(DrawPixelInfo *dpi)
{
	/* Signs are turned off or are invisible */
	if (!HasBit(_display_opt, DO_SHOW_SIGNS) || IsInvisibilitySet(TO_SIGNS)) return;

	const Sign *si;
	FOR_ALL_SIGNS(si) {
		/* Don't draw if sign is owned by another company and competitor signs should be hidden.
		 * Note: It is intentional that also signs owned by OWNER_NONE are hidden. Bankrupt
		 * companies can leave OWNER_NONE signs after them. */
		if (!HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) && _local_company != si->owner && si->owner != OWNER_DEITY) continue;

		ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &si->sign,
				STR_WHITE_SIGN,
				(IsTransparencySet(TO_SIGNS) || si->owner == OWNER_DEITY) ? STR_VIEWPORT_SIGN_SMALL_WHITE : STR_VIEWPORT_SIGN_SMALL_BLACK, STR_NULL,
				si->index, 0, (si->owner == OWNER_NONE) ? COLOUR_GREY : (si->owner == OWNER_DEITY ? INVALID_COLOUR : _company_colours[si->owner]));
	}
}

/**
 * Update the position of the viewport sign.
 * @param center the (preferred) center of the viewport sign
 * @param top    the new top of the sign
 * @param str    the string to show in the sign
 * @param str_small the string to show when zoomed out. STR_NULL means same as \a str
 */
void ViewportSign::UpdatePosition(int center, int top, StringID str, StringID str_small)
{
	if (this->width_normal != 0) this->MarkDirty();

	this->top = top;

	char buffer[DRAW_STRING_BUFFER];

	GetString(buffer, str, lastof(buffer));
	this->width_normal = VPSM_LEFT + Align(GetStringBoundingBox(buffer).width, 2) + VPSM_RIGHT;
	this->center = center;

	/* zoomed out version */
	if (str_small != STR_NULL) {
		GetString(buffer, str_small, lastof(buffer));
	}
	this->width_small = VPSM_LEFT + Align(GetStringBoundingBox(buffer, FS_SMALL).width, 2) + VPSM_RIGHT;

	this->MarkDirty();
}

/**
 * Mark the sign dirty in all viewports.
 * @param maxzoom Maximum %ZoomLevel at which the text is visible.
 *
 * @ingroup dirty
 */
void ViewportSign::MarkDirty(ZoomLevel maxzoom) const
{
	Rect zoomlevels[ZOOM_LVL_COUNT];

	for (ZoomLevel zoom = ZOOM_LVL_BEGIN; zoom != ZOOM_LVL_END; zoom++) {
		/* FIXME: This doesn't switch to width_small when appropriate. */
		zoomlevels[zoom].left   = this->center - ScaleByZoom(this->width_normal / 2 + 1, zoom);
		zoomlevels[zoom].top    = this->top    - ScaleByZoom(1, zoom);
		zoomlevels[zoom].right  = this->center + ScaleByZoom(this->width_normal / 2 + 1, zoom);
		zoomlevels[zoom].bottom = this->top    + ScaleByZoom(VPSM_TOP + FONT_HEIGHT_NORMAL + VPSM_BOTTOM + 1, zoom);
	}

	Window *w;
	FOR_ALL_WINDOWS_FROM_BACK(w) {
		ViewPort *vp = w->viewport;
		if (vp != NULL && vp->zoom <= maxzoom) {
			assert(vp->width != 0);
			Rect &zl = zoomlevels[vp->zoom];
			MarkViewportDirty(vp, zl.left, zl.top, zl.right, zl.bottom);
		}
	}
}

static void ViewportDrawTileSprites(const TileSpriteToDrawVector *tstdv)
{
	const TileSpriteToDraw *tsend = tstdv->End();
	for (const TileSpriteToDraw *ts = tstdv->Begin(); ts != tsend; ++ts) {
		DrawSpriteViewport(ts->image, ts->pal, ts->x, ts->y, ts->sub);
	}
}

/** This fallback sprite checker always exists. */
static bool ViewportSortParentSpritesChecker()
{
	return true;
}

static int CDECL CompareParentSprites(ParentSpriteToDraw * const *psd, ParentSpriteToDraw * const *psd2)
{
	const ParentSpriteToDraw *ps = *psd;
	const ParentSpriteToDraw *ps2 = *psd2;
	return ps->xmin - ps2->xmin;
}

/** Sort parent sprites pointer array */
static void ViewportSortParentSprites(ParentSpriteToSortVector *psdv)
{
	ParentSpriteToDraw **psdvend = psdv->End();
	ParentSpriteToDraw **psd = psdv->Begin();

	/* pre-sort by xmin in ascending order */
	QSortT(psd, psdvend - psd, CompareParentSprites);

	while (psd != psdvend) {
		ParentSpriteToDraw *ps = *psd;

		if (ps->comparison_done) {
			psd++;
			continue;
		}

		ps->comparison_done = true;

		for (ParentSpriteToDraw **psd2 = psd + 1; psd2 != psdvend; psd2++) {
			ParentSpriteToDraw *ps2 = *psd2;

			if (ps2->comparison_done) continue;

			/* Decide which comparator to use, based on whether the bounding
			 * boxes overlap
			 */
			if (ps->xmax >= ps2->xmin && ps->xmin <= ps2->xmax && // overlap in X?
					ps->ymax >= ps2->ymin && ps->ymin <= ps2->ymax && // overlap in Y?
					ps->zmax >= ps2->zmin && ps->zmin <= ps2->zmax) { // overlap in Z?
				/* Use X+Y+Z as the sorting order, so sprites closer to the bottom of
				 * the screen and with higher Z elevation, are drawn in front.
				 * Here X,Y,Z are the coordinates of the "center of mass" of the sprite,
				 * i.e. X=(left+right)/2, etc.
				 * However, since we only care about order, don't actually divide / 2
				 */
				if (ps->xmin + ps->xmax + ps->ymin + ps->ymax + ps->zmin + ps->zmax <=
						ps2->xmin + ps2->xmax + ps2->ymin + ps2->ymax + ps2->zmin + ps2->zmax) {
					continue;
				}
			} else {
				/* We only change the order, if it is definite.
				 * I.e. every single order of X, Y, Z says ps2 is behind ps or they overlap.
				 * That is: If one partial order says ps behind ps2, do not change the order.
				 */
				if (ps->xmax < ps2->xmin) {
					/* all following sprites have xmin >= ps2->xmin */
					break;
				}
				if (ps->ymax < ps2->ymin || ps->zmax < ps2->zmin) {
					continue;
				}
			}

			/* Move ps2 in front of ps */
			ParentSpriteToDraw *temp = ps2;
			for (ParentSpriteToDraw **psd3 = psd2; psd3 > psd; psd3--) {
				*psd3 = *(psd3 - 1);
			}
			*psd = temp;
		}
	}
}

static void ViewportDrawParentSprites(const ParentSpriteToSortVector *psd, const ChildScreenSpriteToDrawVector *csstdv)
{
	const ParentSpriteToDraw * const *psd_end = psd->End();
	for (const ParentSpriteToDraw * const *it = psd->Begin(); it != psd_end; it++) {
		const ParentSpriteToDraw *ps = *it;
		if (ps->image != SPR_EMPTY_BOUNDING_BOX) DrawSpriteViewport(ps->image, ps->pal, ps->x, ps->y, ps->sub);

		int child_idx = ps->first_child;
		while (child_idx >= 0) {
			const ChildScreenSpriteToDraw *cs = csstdv->Get(child_idx);
			child_idx = cs->next;
			DrawSpriteViewport(cs->image, cs->pal, ps->left + cs->x, ps->top + cs->y, cs->sub);
		}
	}
}

/**
 * Draws the bounding boxes of all ParentSprites
 * @param psd Array of ParentSprites
 */
static void ViewportDrawBoundingBoxes(const ParentSpriteToSortVector *psd)
{
	const ParentSpriteToDraw * const *psd_end = psd->End();
	for (const ParentSpriteToDraw * const *it = psd->Begin(); it != psd_end; it++) {
		const ParentSpriteToDraw *ps = *it;
		Point pt1 = RemapCoords(ps->xmax + 1, ps->ymax + 1, ps->zmax + 1); // top front corner
		Point pt2 = RemapCoords(ps->xmin    , ps->ymax + 1, ps->zmax + 1); // top left corner
		Point pt3 = RemapCoords(ps->xmax + 1, ps->ymin    , ps->zmax + 1); // top right corner
		Point pt4 = RemapCoords(ps->xmax + 1, ps->ymax + 1, ps->zmin    ); // bottom front corner

		DrawBox(        pt1.x,         pt1.y,
		        pt2.x - pt1.x, pt2.y - pt1.y,
		        pt3.x - pt1.x, pt3.y - pt1.y,
		        pt4.x - pt1.x, pt4.y - pt1.y);
	}
}

/**
 * Draw/colour the blocks that have been redrawn.
 */
static void ViewportDrawDirtyBlocks()
{
	Blitter *blitter = BlitterFactory::GetCurrentBlitter();
	const DrawPixelInfo *dpi = _cur_dpi;
	void *dst;
	int right =  UnScaleByZoom(dpi->width,  dpi->zoom);
	int bottom = UnScaleByZoom(dpi->height, dpi->zoom);

	int colour = _string_colourmap[_dirty_block_colour & 0xF];

	dst = dpi->dst_ptr;

	byte bo = UnScaleByZoom(dpi->left + dpi->top, dpi->zoom) & 1;
	do {
		for (int i = (bo ^= 1); i < right; i += 2) blitter->SetPixel(dst, i, 0, (uint8)colour);
		dst = blitter->MoveTo(dst, 0, 1);
	} while (--bottom > 0);
}

static void ViewportDrawStrings(ZoomLevel zoom, const StringSpriteToDrawVector *sstdv)
{
	const StringSpriteToDraw *ssend = sstdv->End();
	for (const StringSpriteToDraw *ss = sstdv->Begin(); ss != ssend; ++ss) {
		TextColour colour = TC_BLACK;
		bool small = HasBit(ss->width, 15);
		int w = GB(ss->width, 0, 15);
		int x = UnScaleByZoom(ss->x, zoom);
		int y = UnScaleByZoom(ss->y, zoom);
		int h = VPSM_TOP + (small ? FONT_HEIGHT_SMALL : FONT_HEIGHT_NORMAL) + VPSM_BOTTOM;

		SetDParam(0, ss->params[0]);
		SetDParam(1, ss->params[1]);

		if (ss->colour != INVALID_COLOUR) {
			/* Do not draw signs nor station names if they are set invisible */
			if (IsInvisibilitySet(TO_SIGNS) && ss->string != STR_WHITE_SIGN) continue;

			if (IsTransparencySet(TO_SIGNS) && ss->string != STR_WHITE_SIGN) {
				/* Don't draw the rectangle.
				 * Real colours need the TC_IS_PALETTE_COLOUR flag.
				 * Otherwise colours from _string_colourmap are assumed. */
				colour = (TextColour)_colour_gradient[ss->colour][6] | TC_IS_PALETTE_COLOUR;
			} else {
				/* Draw the rectangle if 'transparent station signs' is off,
				 * or if we are drawing a general text sign (STR_WHITE_SIGN). */
				DrawFrameRect(
					x, y, x + w, y + h, ss->colour,
					IsTransparencySet(TO_SIGNS) ? FR_TRANSPARENT : FR_NONE
				);
			}
		}

		DrawString(x + VPSM_LEFT, x + w - 1 - VPSM_RIGHT, y + VPSM_TOP, ss->string, colour, SA_HOR_CENTER);
	}
}

void ViewportDoDraw(const ViewPort *vp, int left, int top, int right, int bottom)
{
	DrawPixelInfo *old_dpi = _cur_dpi;
	_cur_dpi = &_vd.dpi;

	_vd.dpi.zoom = vp->zoom;
	int mask = ScaleByZoom(-1, vp->zoom);

	_vd.combine_sprites = SPRITE_COMBINE_NONE;

	_vd.dpi.width = (right - left) & mask;
	_vd.dpi.height = (bottom - top) & mask;
	_vd.dpi.left = left & mask;
	_vd.dpi.top = top & mask;
	_vd.dpi.pitch = old_dpi->pitch;
	_vd.last_child = NULL;

	int x = UnScaleByZoom(_vd.dpi.left - (vp->virtual_left & mask), vp->zoom) + vp->left;
	int y = UnScaleByZoom(_vd.dpi.top - (vp->virtual_top & mask), vp->zoom) + vp->top;

	_vd.dpi.dst_ptr = BlitterFactory::GetCurrentBlitter()->MoveTo(old_dpi->dst_ptr, x - old_dpi->left, y - old_dpi->top);

	ViewportAddLandscape();
	ViewportAddVehicles(&_vd.dpi);

	ViewportAddTownNames(&_vd.dpi);
	ViewportAddStationNames(&_vd.dpi);
	ViewportAddSigns(&_vd.dpi);

	DrawTextEffects(&_vd.dpi);

	if (_vd.tile_sprites_to_draw.Length() != 0) ViewportDrawTileSprites(&_vd.tile_sprites_to_draw);

	ParentSpriteToDraw *psd_end = _vd.parent_sprites_to_draw.End();
	for (ParentSpriteToDraw *it = _vd.parent_sprites_to_draw.Begin(); it != psd_end; it++) {
		*_vd.parent_sprites_to_sort.Append() = it;
	}

	_vp_sprite_sorter(&_vd.parent_sprites_to_sort);
	ViewportDrawParentSprites(&_vd.parent_sprites_to_sort, &_vd.child_screen_sprites_to_draw);

	if (_draw_bounding_boxes) ViewportDrawBoundingBoxes(&_vd.parent_sprites_to_sort);
	if (_draw_dirty_blocks) ViewportDrawDirtyBlocks();

	DrawPixelInfo dp = _vd.dpi;
	ZoomLevel zoom = _vd.dpi.zoom;
	dp.zoom = ZOOM_LVL_NORMAL;
	dp.width = UnScaleByZoom(dp.width, zoom);
	dp.height = UnScaleByZoom(dp.height, zoom);
	_cur_dpi = &dp;

	if (vp->overlay != NULL && vp->overlay->GetCargoMask() != 0 && vp->overlay->GetCompanyMask() != 0) {
		/* translate to window coordinates */
		dp.left = x;
		dp.top = y;
		vp->overlay->Draw(&dp);
	}

	if (_vd.string_sprites_to_draw.Length() != 0) {
		/* translate to world coordinates */
		dp.left = UnScaleByZoom(_vd.dpi.left, zoom);
		dp.top = UnScaleByZoom(_vd.dpi.top, zoom);
		ViewportDrawStrings(zoom, &_vd.string_sprites_to_draw);
	}

	_cur_dpi = old_dpi;

	_vd.string_sprites_to_draw.Clear();
	_vd.tile_sprites_to_draw.Clear();
	_vd.parent_sprites_to_draw.Clear();
	_vd.parent_sprites_to_sort.Clear();
	_vd.child_screen_sprites_to_draw.Clear();
}

/**
 * Make sure we don't draw a too big area at a time.
 * If we do, the sprite memory will overflow.
 */
static void ViewportDrawChk(const ViewPort *vp, int left, int top, int right, int bottom)
{
	if (ScaleByZoom(bottom - top, vp->zoom) * ScaleByZoom(right - left, vp->zoom) > 180000 * ZOOM_LVL_BASE * ZOOM_LVL_BASE) {
		if ((bottom - top) > (right - left)) {
			int t = (top + bottom) >> 1;
			ViewportDrawChk(vp, left, top, right, t);
			ViewportDrawChk(vp, left, t, right, bottom);
		} else {
			int t = (left + right) >> 1;
			ViewportDrawChk(vp, left, top, t, bottom);
			ViewportDrawChk(vp, t, top, right, bottom);
		}
	} else {
		ViewportDoDraw(vp,
			ScaleByZoom(left - vp->left, vp->zoom) + vp->virtual_left,
			ScaleByZoom(top - vp->top, vp->zoom) + vp->virtual_top,
			ScaleByZoom(right - vp->left, vp->zoom) + vp->virtual_left,
			ScaleByZoom(bottom - vp->top, vp->zoom) + vp->virtual_top
		);
	}
}

static inline void ViewportDraw(const ViewPort *vp, int left, int top, int right, int bottom)
{
	if (right <= vp->left || bottom <= vp->top) return;

	if (left >= vp->left + vp->width) return;

	if (left < vp->left) left = vp->left;
	if (right > vp->left + vp->width) right = vp->left + vp->width;

	if (top >= vp->top + vp->height) return;

	if (top < vp->top) top = vp->top;
	if (bottom > vp->top + vp->height) bottom = vp->top + vp->height;

	ViewportDrawChk(vp, left, top, right, bottom);
}

/**
 * Draw the viewport of this window.
 */
void Window::DrawViewport() const
{
	PerformanceAccumulator framerate(PFE_DRAWWORLD);

	DrawPixelInfo *dpi = _cur_dpi;

	dpi->left += this->left;
	dpi->top += this->top;

	ViewportDraw(this->viewport, dpi->left, dpi->top, dpi->left + dpi->width, dpi->top + dpi->height);

	dpi->left -= this->left;
	dpi->top -= this->top;
}

/**
 * Continue criteria for the SearchMapEdge function.
 * @param iter       Value to check.
 * @param iter_limit Maximum value for the iter
 * @param sy         Screen y coordinate calculated for the tile at hand
 * @param sy_limit   Limit to the screen y coordinate
 * @return True when we should continue searching.
 */
typedef bool ContinueMapEdgeSearch(int iter, int iter_limit, int sy, int sy_limit);

/** Continue criteria for searching a no-longer-visible tile in negative direction, starting at some tile. */
static inline bool ContinueLowerMapEdgeSearch(int iter, int iter_limit, int sy, int sy_limit) { return iter > 0          && sy > sy_limit; }
/** Continue criteria for searching a no-longer-visible tile in positive direction, starting at some tile. */
static inline bool ContinueUpperMapEdgeSearch(int iter, int iter_limit, int sy, int sy_limit) { return iter < iter_limit && sy < sy_limit; }

/**
 * Searches, starting at the given tile, by applying the given offset to iter, for a no longer visible tile.
 * The whole sense of this function is keeping the to-be-written code small, thus it is a little bit abstracted
 * so the same function can be used for both the X and Y locations. As such a reference to one of the elements
 * in curr_tile was needed.
 * @param curr_tile  A tile
 * @param iter       Reference to either the X or Y of curr_tile.
 * @param iter_limit Upper search limit for the iter value.
 * @param offset     Search in steps of this size
 * @param sy_limit   Search limit to be passed to the criteria
 * @param continue_criteria Search as long as this criteria is true
 * @return The final value of iter.
 */
static int SearchMapEdge(Point &curr_tile, int &iter, int iter_limit, int offset, int sy_limit, ContinueMapEdgeSearch continue_criteria)
{
	int sy;
	do {
		iter = Clamp(iter + offset, 0, iter_limit);
		sy = GetViewportY(curr_tile);
	} while (continue_criteria(iter, iter_limit, sy, sy_limit));

	return iter;
}

/**
 * Determine the clamping of either the X or Y coordinate to the map.
 * @param curr_tile   A tile
 * @param iter        Reference to either the X or Y of curr_tile.
 * @param iter_limit  Upper search limit for the iter value.
 * @param start       Start value for the iteration.
 * @param other_ref   Reference to the opposite axis in curr_tile than of iter.
 * @param other_value Start value for of the opposite axis
 * @param vp_value    Value of the viewport location in the opposite axis as for iter.
 * @param other_limit Limit for the other value, so if iter is X, then other_limit is for Y.
 * @param vp_top      Top of the viewport.
 * @param vp_bottom   Bottom of the viewport.
 * @return Clamped version of vp_value.
 */
static inline int ClampXYToMap(Point &curr_tile, int &iter, int iter_limit, int start, int &other_ref, int other_value, int vp_value, int other_limit, int vp_top, int vp_bottom)
{
	bool upper_edge = other_value < _settings_game.construction.max_heightlevel / 4;

	/*
	 * First get an estimate of the tiles relevant for us at that edge.  Relevant in the sense
	 * "at least close to the visible area". Thus, we don't look at exactly each tile, inspecting
	 * e.g. every tenth should be enough. After all, the desired screen limit is set such that
	 * the bordermost tiles are painted in the middle of the screen when one hits the limit,
	 * i.e. it is no harm if there is some small error in that calculation
	 */

	other_ref = upper_edge ? 0 : other_limit;
	iter = start;
	int min_iter = SearchMapEdge(curr_tile, iter, iter_limit, upper_edge ? -10 : +10, vp_top,    upper_edge ? ContinueLowerMapEdgeSearch : ContinueUpperMapEdgeSearch);
	iter = start;
	int max_iter = SearchMapEdge(curr_tile, iter, iter_limit, upper_edge ? +10 : -10, vp_bottom, upper_edge ? ContinueUpperMapEdgeSearch : ContinueLowerMapEdgeSearch);

	max_iter = min(max_iter + _settings_game.construction.max_heightlevel / 4, iter_limit);
	min_iter = min(min_iter, max_iter);

	/* Now, calculate the highest heightlevel of these tiles. Again just as an estimate. */
	int max_heightlevel_at_edge = 0;
	for (iter = min_iter; iter <= max_iter; iter += 10) {
		max_heightlevel_at_edge = max(max_heightlevel_at_edge, (int)TileHeight(TileXY(curr_tile.x, curr_tile.y)));
	}

	/* Based on that heightlevel, calculate the limit. For the upper edge a tile with height zero would
	 * get a limit of zero, on the other side it depends on the number of tiles along the axis. */
	return upper_edge ?
			max(vp_value, -max_heightlevel_at_edge * (int)(TILE_HEIGHT * 2 * ZOOM_LVL_BASE)) :
			min(vp_value, (other_limit * TILE_SIZE * 4 - max_heightlevel_at_edge * TILE_HEIGHT * 2) * ZOOM_LVL_BASE);
}

static inline void ClampViewportToMap(const ViewPort *vp, int &x, int &y)
{
	int original_y = y;

	/* Centre of the viewport is hot spot */
	x += vp->virtual_width / 2;
	y += vp->virtual_height / 2;

	/* Convert viewport coordinates to map coordinates
	 * Calculation is scaled by 4 to avoid rounding errors */
	int vx = -x + y * 2;
	int vy =  x + y * 2;

	/* Find out which tile corresponds to (vx,vy) if one assumes height zero.  The cast is necessary to prevent C++ from
	 * converting the result to an uint, which gives an overflow instead of a negative result... */
	int tx = vx / (int)(TILE_SIZE * 4 * ZOOM_LVL_BASE);
	int ty = vy / (int)(TILE_SIZE * 4 * ZOOM_LVL_BASE);

	Point curr_tile;
	vx = ClampXYToMap(curr_tile, curr_tile.y, MapMaxY(), ty, curr_tile.x, tx, vx, MapMaxX(), original_y, original_y + vp->virtual_height);
	vy = ClampXYToMap(curr_tile, curr_tile.x, MapMaxX(), tx, curr_tile.y, ty, vy, MapMaxY(), original_y, original_y + vp->virtual_height);

	/* Convert map coordinates to viewport coordinates */
	x = (-vx + vy) / 2;
	y = ( vx + vy) / 4;

	/* Remove centering */
	x -= vp->virtual_width / 2;
	y -= vp->virtual_height / 2;
}

/**
 * Update the viewport position being displayed.
 * @param w %Window owning the viewport.
 */
void UpdateViewportPosition(Window *w)
{
	const ViewPort *vp = w->viewport;

	if (w->viewport->follow_vehicle != INVALID_VEHICLE) {
		const Vehicle *veh = Vehicle::Get(w->viewport->follow_vehicle);
		Point pt = MapXYZToViewport(vp, veh->x_pos, veh->y_pos, veh->z_pos);

		w->viewport->scrollpos_x = pt.x;
		w->viewport->scrollpos_y = pt.y;
		SetViewportPosition(w, pt.x, pt.y);
	} else {
		/* Ensure the destination location is within the map */
		ClampViewportToMap(vp, w->viewport->dest_scrollpos_x, w->viewport->dest_scrollpos_y);

		int delta_x = w->viewport->dest_scrollpos_x - w->viewport->scrollpos_x;
		int delta_y = w->viewport->dest_scrollpos_y - w->viewport->scrollpos_y;

		bool update_overlay = false;
		if (delta_x != 0 || delta_y != 0) {
			if (_settings_client.gui.smooth_scroll) {
				int max_scroll = ScaleByMapSize1D(512 * ZOOM_LVL_BASE);
				/* Not at our desired position yet... */
				w->viewport->scrollpos_x += Clamp(delta_x / 4, -max_scroll, max_scroll);
				w->viewport->scrollpos_y += Clamp(delta_y / 4, -max_scroll, max_scroll);
			} else {
				w->viewport->scrollpos_x = w->viewport->dest_scrollpos_x;
				w->viewport->scrollpos_y = w->viewport->dest_scrollpos_y;
			}
			update_overlay = (w->viewport->scrollpos_x == w->viewport->dest_scrollpos_x &&
								w->viewport->scrollpos_y == w->viewport->dest_scrollpos_y);
		}

		ClampViewportToMap(vp, w->viewport->scrollpos_x, w->viewport->scrollpos_y);

		SetViewportPosition(w, w->viewport->scrollpos_x, w->viewport->scrollpos_y);
		if (update_overlay) RebuildViewportOverlay(w);
	}
}

/**
 * Marks a viewport as dirty for repaint if it displays (a part of) the area the needs to be repainted.
 * @param vp     The viewport to mark as dirty
 * @param left   Left edge of area to repaint
 * @param top    Top edge of area to repaint
 * @param right  Right edge of area to repaint
 * @param bottom Bottom edge of area to repaint
 * @ingroup dirty
 */
static void MarkViewportDirty(const ViewPort *vp, int left, int top, int right, int bottom)
{
	/* Rounding wrt. zoom-out level */
	right  += (1 << vp->zoom) - 1;
	bottom += (1 << vp->zoom) - 1;

	right -= vp->virtual_left;
	if (right <= 0) return;

	bottom -= vp->virtual_top;
	if (bottom <= 0) return;

	left = max(0, left - vp->virtual_left);

	if (left >= vp->virtual_width) return;

	top = max(0, top - vp->virtual_top);

	if (top >= vp->virtual_height) return;

	SetDirtyBlocks(
		UnScaleByZoomLower(left, vp->zoom) + vp->left,
		UnScaleByZoomLower(top, vp->zoom) + vp->top,
		UnScaleByZoom(right, vp->zoom) + vp->left + 1,
		UnScaleByZoom(bottom, vp->zoom) + vp->top + 1
	);
}

/**
 * Mark all viewports that display an area as dirty (in need of repaint).
 * @param left   Left   edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param top    Top    edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param right  Right  edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param bottom Bottom edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @ingroup dirty
 */
void MarkAllViewportsDirty(int left, int top, int right, int bottom)
{
	Window *w;
	FOR_ALL_WINDOWS_FROM_BACK(w) {
		ViewPort *vp = w->viewport;
		if (vp != NULL) {
			assert(vp->width != 0);
			MarkViewportDirty(vp, left, top, right, bottom);
		}
	}
}

void ConstrainAllViewportsZoom()
{
	Window *w;
	FOR_ALL_WINDOWS_FROM_FRONT(w) {
		if (w->viewport == NULL) continue;

		ZoomLevel zoom = static_cast<ZoomLevel>(Clamp(w->viewport->zoom, _settings_client.gui.zoom_min, _settings_client.gui.zoom_max));
		if (zoom != w->viewport->zoom) {
			while (w->viewport->zoom < zoom) DoZoomInOutWindow(ZOOM_OUT, w);
			while (w->viewport->zoom > zoom) DoZoomInOutWindow(ZOOM_IN, w);
		}
	}
}

/**
 * Mark a tile given by its index dirty for repaint.
 * @param tile The tile to mark dirty.
 * @param bridge_level_offset Height of bridge on tile to also mark dirty. (Height level relative to north corner.)
 * @ingroup dirty
 */
void MarkTileDirtyByTile(TileIndex tile, int bridge_level_offset)
{
	Point pt = RemapCoords(TileX(tile) * TILE_SIZE, TileY(tile) * TILE_SIZE, TilePixelHeight(tile));
	MarkAllViewportsDirty(
			pt.x - MAX_TILE_EXTENT_LEFT,
			pt.y - MAX_TILE_EXTENT_TOP - ZOOM_LVL_BASE * TILE_HEIGHT * bridge_level_offset,
			pt.x + MAX_TILE_EXTENT_RIGHT,
			pt.y + MAX_TILE_EXTENT_BOTTOM);
}

/**
 * Mark a (virtual) tile outside the map dirty for repaint.
 * @param x Tile X position.
 * @param y Tile Y position.
 * @ingroup dirty
 */
void MarkTileDirtyByTileOutsideMap(int x, int y)
{
	Point pt = RemapCoords(x * TILE_SIZE, y * TILE_SIZE, TilePixelHeightOutsideMap(x, y));
	MarkAllViewportsDirty(
			pt.x - MAX_TILE_EXTENT_LEFT,
			pt.y, // no buildings outside of map
			pt.x + MAX_TILE_EXTENT_RIGHT,
			pt.y + MAX_TILE_EXTENT_BOTTOM);
}

/**
 * Marks the selected tiles as dirty.
 *
 * This function marks the selected tiles as dirty for repaint
 *
 * @ingroup dirty
 */
static void SetSelectionTilesDirty()
{
	int x_size = _thd.size.x;
	int y_size = _thd.size.y;

	if (!_thd.diagonal) { // Selecting in a straight rectangle (or a single square)
		int x_start = _thd.pos.x;
		int y_start = _thd.pos.y;

		if (_thd.outersize.x != 0) {
			x_size  += _thd.outersize.x;
			x_start += _thd.offs.x;
			y_size  += _thd.outersize.y;
			y_start += _thd.offs.y;
		}

		x_size -= TILE_SIZE;
		y_size -= TILE_SIZE;

		assert(x_size >= 0);
		assert(y_size >= 0);

		int x_end = Clamp(x_start + x_size, 0, MapSizeX() * TILE_SIZE - TILE_SIZE);
		int y_end = Clamp(y_start + y_size, 0, MapSizeY() * TILE_SIZE - TILE_SIZE);

		x_start = Clamp(x_start, 0, MapSizeX() * TILE_SIZE - TILE_SIZE);
		y_start = Clamp(y_start, 0, MapSizeY() * TILE_SIZE - TILE_SIZE);

		/* make sure everything is multiple of TILE_SIZE */
		assert((x_end | y_end | x_start | y_start) % TILE_SIZE == 0);

		/* How it works:
		 * Suppose we have to mark dirty rectangle of 3x4 tiles:
		 *   x
		 *  xxx
		 * xxxxx
		 *  xxxxx
		 *   xxx
		 *    x
		 * This algorithm marks dirty columns of tiles, so it is done in 3+4-1 steps:
		 * 1)  x     2)  x
		 *    xxx       Oxx
		 *   Oxxxx     xOxxx
		 *    xxxxx     Oxxxx
		 *     xxx       xxx
		 *      x         x
		 * And so forth...
		 */

		int top_x = x_end; // coordinates of top dirty tile
		int top_y = y_start;
		int bot_x = top_x; // coordinates of bottom dirty tile
		int bot_y = top_y;

		do {
			/* topmost dirty point */
			TileIndex top_tile = TileVirtXY(top_x, top_y);
			Point top = RemapCoords(top_x, top_y, GetTileMaxPixelZ(top_tile));

			/* bottommost point */
			TileIndex bottom_tile = TileVirtXY(bot_x, bot_y);
			Point bot = RemapCoords(bot_x + TILE_SIZE, bot_y + TILE_SIZE, GetTilePixelZ(bottom_tile)); // bottommost point

			/* the 'x' coordinate of 'top' and 'bot' is the same (and always in the same distance from tile middle),
			 * tile height/slope affects only the 'y' on-screen coordinate! */

			int l = top.x - TILE_PIXELS * ZOOM_LVL_BASE; // 'x' coordinate of left   side of the dirty rectangle
			int t = top.y;                               // 'y' coordinate of top    side of the dirty rectangle
			int r = top.x + TILE_PIXELS * ZOOM_LVL_BASE; // 'x' coordinate of right  side of the dirty rectangle
			int b = bot.y;                               // 'y' coordinate of bottom side of the dirty rectangle

			static const int OVERLAY_WIDTH = 4 * ZOOM_LVL_BASE; // part of selection sprites is drawn outside the selected area (in particular: terraforming)

			/* For halftile foundations on SLOPE_STEEP_S the sprite extents some more towards the top */
			MarkAllViewportsDirty(l - OVERLAY_WIDTH, t - OVERLAY_WIDTH - TILE_HEIGHT * ZOOM_LVL_BASE, r + OVERLAY_WIDTH, b + OVERLAY_WIDTH);

			/* haven't we reached the topmost tile yet? */
			if (top_x != x_start) {
				top_x -= TILE_SIZE;
			} else {
				top_y += TILE_SIZE;
			}

			/* the way the bottom tile changes is different when we reach the bottommost tile */
			if (bot_y != y_end) {
				bot_y += TILE_SIZE;
			} else {
				bot_x -= TILE_SIZE;
			}
		} while (bot_x >= top_x);
	} else { // Selecting in a 45 degrees rotated (diagonal) rectangle.
		/* a_size, b_size describe a rectangle with rotated coordinates */
		int a_size = x_size + y_size, b_size = x_size - y_size;

		int interval_a = a_size < 0 ? -(int)TILE_SIZE : (int)TILE_SIZE;
		int interval_b = b_size < 0 ? -(int)TILE_SIZE : (int)TILE_SIZE;

		for (int a = -interval_a; a != a_size + interval_a; a += interval_a) {
			for (int b = -interval_b; b != b_size + interval_b; b += interval_b) {
				uint x = (_thd.pos.x + (a + b) / 2) / TILE_SIZE;
				uint y = (_thd.pos.y + (a - b) / 2) / TILE_SIZE;

				if (x < MapMaxX() && y < MapMaxY()) {
					MarkTileDirtyByTile(TileXY(x, y));
				}
			}
		}
	}
}


void SetSelectionRed(bool b)
{
	_thd.make_square_red = b;
	SetSelectionTilesDirty();
}

/**
 * Test whether a sign is below the mouse
 * @param vp the clicked viewport
 * @param x X position of click
 * @param y Y position of click
 * @param sign the sign to check
 * @return true if the sign was hit
 */
static bool CheckClickOnViewportSign(const ViewPort *vp, int x, int y, const ViewportSign *sign)
{
	bool small = (vp->zoom >= ZOOM_LVL_OUT_16X);
	int sign_half_width = ScaleByZoom((small ? sign->width_small : sign->width_normal) / 2, vp->zoom);
	int sign_height = ScaleByZoom(VPSM_TOP + (small ? FONT_HEIGHT_SMALL : FONT_HEIGHT_NORMAL) + VPSM_BOTTOM, vp->zoom);

	x = ScaleByZoom(x - vp->left, vp->zoom) + vp->virtual_left;
	y = ScaleByZoom(y - vp->top, vp->zoom) + vp->virtual_top;

	return y >= sign->top && y < sign->top + sign_height &&
			x >= sign->center - sign_half_width && x < sign->center + sign_half_width;
}

static bool CheckClickOnTown(const ViewPort *vp, int x, int y)
{
	if (!HasBit(_display_opt, DO_SHOW_TOWN_NAMES)) return false;

	const Town *t;
	FOR_ALL_TOWNS(t) {
		if (CheckClickOnViewportSign(vp, x, y, &t->cache.sign)) {
			ShowTownViewWindow(t->index);
			return true;
		}
	}

	return false;
}

static bool CheckClickOnStation(const ViewPort *vp, int x, int y)
{
	if (!(HasBit(_display_opt, DO_SHOW_STATION_NAMES) || HasBit(_display_opt, DO_SHOW_WAYPOINT_NAMES)) || IsInvisibilitySet(TO_SIGNS)) return false;

	const BaseStation *st;
	FOR_ALL_BASE_STATIONS(st) {
		/* Check whether the base station is a station or a waypoint */
		bool is_station = Station::IsExpected(st);

		/* Don't check if the display options are disabled */
		if (!HasBit(_display_opt, is_station ? DO_SHOW_STATION_NAMES : DO_SHOW_WAYPOINT_NAMES)) continue;

		/* Don't check if competitor signs are not shown and the sign isn't owned by the local company */
		if (!HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) && _local_company != st->owner && st->owner != OWNER_NONE) continue;

		if (CheckClickOnViewportSign(vp, x, y, &st->sign)) {
			if (is_station) {
				ShowStationViewWindow(st->index);
			} else {
				ShowWaypointWindow(Waypoint::From(st));
			}
			return true;
		}
	}

	return false;
}


static bool CheckClickOnSign(const ViewPort *vp, int x, int y)
{
	/* Signs are turned off, or they are transparent and invisibility is ON, or company is a spectator */
	if (!HasBit(_display_opt, DO_SHOW_SIGNS) || IsInvisibilitySet(TO_SIGNS) || _local_company == COMPANY_SPECTATOR) return false;

	const Sign *si;
	FOR_ALL_SIGNS(si) {
		/* If competitor signs are hidden, don't check signs that aren't owned by local company */
		if (!HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) && _local_company != si->owner && si->owner != OWNER_DEITY) continue;
		if (si->owner == OWNER_DEITY && _game_mode != GM_EDITOR) continue;

		if (CheckClickOnViewportSign(vp, x, y, &si->sign)) {
			HandleClickOnSign(si);
			return true;
		}
	}

	return false;
}


static bool CheckClickOnLandscape(const ViewPort *vp, int x, int y)
{
	Point pt = TranslateXYToTileCoord(vp, x, y);

	if (pt.x != -1) return ClickTile(TileVirtXY(pt.x, pt.y));
	return true;
}

static void PlaceObject()
{
	Point pt;
	Window *w;

	pt = GetTileBelowCursor();
	if (pt.x == -1) return;

	if ((_thd.place_mode & HT_DRAG_MASK) == HT_POINT) {
		pt.x += TILE_SIZE / 2;
		pt.y += TILE_SIZE / 2;
	}

	_tile_fract_coords.x = pt.x & TILE_UNIT_MASK;
	_tile_fract_coords.y = pt.y & TILE_UNIT_MASK;

	w = _thd.GetCallbackWnd();
	if (w != NULL) w->OnPlaceObject(pt, TileVirtXY(pt.x, pt.y));
}


bool HandleViewportClicked(const ViewPort *vp, int x, int y)
{
	const Vehicle *v = CheckClickOnVehicle(vp, x, y);

	if (_thd.place_mode & HT_VEHICLE) {
		if (v != NULL && VehicleClicked(v)) return true;
	}

	/* Vehicle placement mode already handled above. */
	if ((_thd.place_mode & HT_DRAG_MASK) != HT_NONE) {
		PlaceObject();
		return true;
	}

	if (CheckClickOnTown(vp, x, y)) return true;
	if (CheckClickOnStation(vp, x, y)) return true;
	if (CheckClickOnSign(vp, x, y)) return true;
	bool result = CheckClickOnLandscape(vp, x, y);

	if (v != NULL) {
		DEBUG(misc, 2, "Vehicle %d (index %d) at %p", v->unitnumber, v->index, v);
		if (IsCompanyBuildableVehicleType(v)) {
			v = v->First();
			if (_ctrl_pressed && v->owner == _local_company) {
				StartStopVehicle(v, true);
			} else {
				ShowVehicleViewWindow(v);
			}
		}
		return true;
	}
	return result;
}

void RebuildViewportOverlay(Window *w)
{
	if (w->viewport->overlay != NULL &&
			w->viewport->overlay->GetCompanyMask() != 0 &&
			w->viewport->overlay->GetCargoMask() != 0) {
		w->viewport->overlay->RebuildCache();
		w->SetDirty();
	}
}

/**
 * Scrolls the viewport in a window to a given location.
 * @param x       Desired x location of the map to scroll to (world coordinate).
 * @param y       Desired y location of the map to scroll to (world coordinate).
 * @param z       Desired z location of the map to scroll to (world coordinate). Use \c -1 to scroll to the height of the map at the \a x, \a y location.
 * @param w       %Window containing the viewport.
 * @param instant Jump to the location instead of slowly moving to it.
 * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
 */
bool ScrollWindowTo(int x, int y, int z, Window *w, bool instant)
{
	/* The slope cannot be acquired outside of the map, so make sure we are always within the map. */
	if (z == -1) {
		if ( x >= 0 && x <= (int)MapSizeX() * (int)TILE_SIZE - 1
				&& y >= 0 && y <= (int)MapSizeY() * (int)TILE_SIZE - 1) {
			z = GetSlopePixelZ(x, y);
		} else {
			z = TileHeightOutsideMap(x / (int)TILE_SIZE, y / (int)TILE_SIZE);
		}
	}

	Point pt = MapXYZToViewport(w->viewport, x, y, z);
	w->viewport->follow_vehicle = INVALID_VEHICLE;

	if (w->viewport->dest_scrollpos_x == pt.x && w->viewport->dest_scrollpos_y == pt.y) return false;

	if (instant) {
		w->viewport->scrollpos_x = pt.x;
		w->viewport->scrollpos_y = pt.y;
		RebuildViewportOverlay(w);
	}

	w->viewport->dest_scrollpos_x = pt.x;
	w->viewport->dest_scrollpos_y = pt.y;
	return true;
}

/**
 * Scrolls the viewport in a window to a given location.
 * @param tile    Desired tile to center on.
 * @param w       %Window containing the viewport.
 * @param instant Jump to the location instead of slowly moving to it.
 * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
 */
bool ScrollWindowToTile(TileIndex tile, Window *w, bool instant)
{
	return ScrollWindowTo(TileX(tile) * TILE_SIZE, TileY(tile) * TILE_SIZE, -1, w, instant);
}

/**
 * Scrolls the viewport of the main window to a given location.
 * @param tile    Desired tile to center on.
 * @param instant Jump to the location instead of slowly moving to it.
 * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
 */
bool ScrollMainWindowToTile(TileIndex tile, bool instant)
{
	return ScrollMainWindowTo(TileX(tile) * TILE_SIZE + TILE_SIZE / 2, TileY(tile) * TILE_SIZE + TILE_SIZE / 2, -1, instant);
}

/**
 * Set a tile to display a red error square.
 * @param tile Tile that should show the red error square.
 */
void SetRedErrorSquare(TileIndex tile)
{
	TileIndex old;

	old = _thd.redsq;
	_thd.redsq = tile;

	if (tile != old) {
		if (tile != INVALID_TILE) MarkTileDirtyByTile(tile);
		if (old  != INVALID_TILE) MarkTileDirtyByTile(old);
	}
}

/**
 * Highlight \a w by \a h tiles at the cursor.
 * @param w Width of the highlighted tiles rectangle.
 * @param h Height of the highlighted tiles rectangle.
 */
void SetTileSelectSize(int w, int h)
{
	_thd.new_size.x = w * TILE_SIZE;
	_thd.new_size.y = h * TILE_SIZE;
	_thd.new_outersize.x = 0;
	_thd.new_outersize.y = 0;
}

void SetTileSelectBigSize(int ox, int oy, int sx, int sy)
{
	_thd.offs.x = ox * TILE_SIZE;
	_thd.offs.y = oy * TILE_SIZE;
	_thd.new_outersize.x = sx * TILE_SIZE;
	_thd.new_outersize.y = sy * TILE_SIZE;
}

/** returns the best autorail highlight type from map coordinates */
static HighLightStyle GetAutorailHT(int x, int y)
{
	return HT_RAIL | _autorail_piece[x & TILE_UNIT_MASK][y & TILE_UNIT_MASK];
}

/**
 * Reset tile highlighting.
 */
void TileHighlightData::Reset()
{
	this->pos.x = 0;
	this->pos.y = 0;
	this->new_pos.x = 0;
	this->new_pos.y = 0;
}

/**
 * Is the user dragging a 'diagonal rectangle'?
 * @return User is dragging a rotated rectangle.
 */
bool TileHighlightData::IsDraggingDiagonal()
{
	return (this->place_mode & HT_DIAGONAL) != 0 && _ctrl_pressed && _left_button_down;
}

/**
 * Get the window that started the current highlighting.
 * @return The window that requested the current tile highlighting, or \c NULL if not available.
 */
Window *TileHighlightData::GetCallbackWnd()
{
	return FindWindowById(this->window_class, this->window_number);
}



/**
 * Updates tile highlighting for all cases.
 * Uses _thd.selstart and _thd.selend and _thd.place_mode (set elsewhere) to determine _thd.pos and _thd.size
 * Also drawstyle is determined. Uses _thd.new.* as a buffer and calls SetSelectionTilesDirty() twice,
 * Once for the old and once for the new selection.
 * _thd is TileHighlightData, found in viewport.h
 */
void UpdateTileSelection()
{
	int x1;
	int y1;

	HighLightStyle new_drawstyle = HT_NONE;
	bool new_diagonal = false;

	if ((_thd.place_mode & HT_DRAG_MASK) == HT_SPECIAL) {
		x1 = _thd.selend.x;
		y1 = _thd.selend.y;
		if (x1 != -1) {
			int x2 = _thd.selstart.x & ~TILE_UNIT_MASK;
			int y2 = _thd.selstart.y & ~TILE_UNIT_MASK;
			x1 &= ~TILE_UNIT_MASK;
			y1 &= ~TILE_UNIT_MASK;

			if (_thd.IsDraggingDiagonal()) {
				new_diagonal = true;
			} else {
				if (x1 >= x2) Swap(x1, x2);
				if (y1 >= y2) Swap(y1, y2);
			}
			_thd.new_pos.x = x1;
			_thd.new_pos.y = y1;
			_thd.new_size.x = x2 - x1;
			_thd.new_size.y = y2 - y1;
			if (!new_diagonal) {
				_thd.new_size.x += TILE_SIZE;
				_thd.new_size.y += TILE_SIZE;
			}
			new_drawstyle = _thd.next_drawstyle;
		}
	} else if ((_thd.place_mode & HT_DRAG_MASK) != HT_NONE) {
		Point pt = GetTileBelowCursor();
		x1 = pt.x;
		y1 = pt.y;
		if (x1 != -1) {
			switch (_thd.place_mode & HT_DRAG_MASK) {
				case HT_RECT:
					new_drawstyle = HT_RECT;
					break;
				case HT_POINT:
					new_drawstyle = HT_POINT;
					x1 += TILE_SIZE / 2;
					y1 += TILE_SIZE / 2;
					break;
				case HT_RAIL:
					/* Draw one highlighted tile in any direction */
					new_drawstyle = GetAutorailHT(pt.x, pt.y);
					break;
				case HT_LINE:
					switch (_thd.place_mode & HT_DIR_MASK) {
						case HT_DIR_X: new_drawstyle = HT_LINE | HT_DIR_X; break;
						case HT_DIR_Y: new_drawstyle = HT_LINE | HT_DIR_Y; break;

						case HT_DIR_HU:
						case HT_DIR_HL:
							new_drawstyle = (pt.x & TILE_UNIT_MASK) + (pt.y & TILE_UNIT_MASK) <= TILE_SIZE ? HT_LINE | HT_DIR_HU : HT_LINE | HT_DIR_HL;
							break;

						case HT_DIR_VL:
						case HT_DIR_VR:
							new_drawstyle = (pt.x & TILE_UNIT_MASK) > (pt.y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
							break;

						default: NOT_REACHED();
					}
					_thd.selstart.x = x1 & ~TILE_UNIT_MASK;
					_thd.selstart.y = y1 & ~TILE_UNIT_MASK;
					break;
				default:
					NOT_REACHED();
			}
			_thd.new_pos.x = x1 & ~TILE_UNIT_MASK;
			_thd.new_pos.y = y1 & ~TILE_UNIT_MASK;
		}
	}

	/* redraw selection */
	if (_thd.drawstyle != new_drawstyle ||
			_thd.pos.x != _thd.new_pos.x || _thd.pos.y != _thd.new_pos.y ||
			_thd.size.x != _thd.new_size.x || _thd.size.y != _thd.new_size.y ||
			_thd.outersize.x != _thd.new_outersize.x ||
			_thd.outersize.y != _thd.new_outersize.y ||
			_thd.diagonal    != new_diagonal) {
		/* Clear the old tile selection? */
		if ((_thd.drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();

		_thd.drawstyle = new_drawstyle;
		_thd.pos = _thd.new_pos;
		_thd.size = _thd.new_size;
		_thd.outersize = _thd.new_outersize;
		_thd.diagonal = new_diagonal;
		_thd.dirty = 0xff;

		/* Draw the new tile selection? */
		if ((new_drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();
	}
}

/**
 * Displays the measurement tooltips when selecting multiple tiles
 * @param str String to be displayed
 * @param paramcount number of params to deal with
 * @param params (optional) up to 5 pieces of additional information that may be added to a tooltip
 * @param close_cond Condition for closing this tooltip.
 */
static inline void ShowMeasurementTooltips(StringID str, uint paramcount, const uint64 params[], TooltipCloseCondition close_cond = TCC_LEFT_CLICK)
{
	if (!_settings_client.gui.measure_tooltip) return;
	GuiShowTooltips(_thd.GetCallbackWnd(), str, paramcount, params, close_cond);
}

/** highlighting tiles while only going over them with the mouse */
void VpStartPlaceSizing(TileIndex tile, ViewportPlaceMethod method, ViewportDragDropSelectionProcess process)
{
	_thd.select_method = method;
	_thd.select_proc   = process;
	_thd.selend.x = TileX(tile) * TILE_SIZE;
	_thd.selstart.x = TileX(tile) * TILE_SIZE;
	_thd.selend.y = TileY(tile) * TILE_SIZE;
	_thd.selstart.y = TileY(tile) * TILE_SIZE;

	/* Needed so several things (road, autoroad, bridges, ...) are placed correctly.
	 * In effect, placement starts from the centre of a tile
	 */
	if (method == VPM_X_OR_Y || method == VPM_FIX_X || method == VPM_FIX_Y) {
		_thd.selend.x += TILE_SIZE / 2;
		_thd.selend.y += TILE_SIZE / 2;
		_thd.selstart.x += TILE_SIZE / 2;
		_thd.selstart.y += TILE_SIZE / 2;
	}

	HighLightStyle others = _thd.place_mode & ~(HT_DRAG_MASK | HT_DIR_MASK);
	if ((_thd.place_mode & HT_DRAG_MASK) == HT_RECT) {
		_thd.place_mode = HT_SPECIAL | others;
		_thd.next_drawstyle = HT_RECT | others;
	} else if (_thd.place_mode & (HT_RAIL | HT_LINE)) {
		_thd.place_mode = HT_SPECIAL | others;
		_thd.next_drawstyle = _thd.drawstyle | others;
	} else {
		_thd.place_mode = HT_SPECIAL | others;
		_thd.next_drawstyle = HT_POINT | others;
	}
	_special_mouse_mode = WSM_SIZING;
}

void VpSetPlaceSizingLimit(int limit)
{
	_thd.sizelimit = limit;
}

/**
 * Highlights all tiles between a set of two tiles. Used in dock and tunnel placement
 * @param from TileIndex of the first tile to highlight
 * @param to TileIndex of the last tile to highlight
 */
void VpSetPresizeRange(TileIndex from, TileIndex to)
{
	uint64 distance = DistanceManhattan(from, to) + 1;

	_thd.selend.x = TileX(to) * TILE_SIZE;
	_thd.selend.y = TileY(to) * TILE_SIZE;
	_thd.selstart.x = TileX(from) * TILE_SIZE;
	_thd.selstart.y = TileY(from) * TILE_SIZE;
	_thd.next_drawstyle = HT_RECT;

	/* show measurement only if there is any length to speak of */
	if (distance > 1) ShowMeasurementTooltips(STR_MEASURE_LENGTH, 1, &distance, TCC_HOVER);
}

static void VpStartPreSizing()
{
	_thd.selend.x = -1;
	_special_mouse_mode = WSM_PRESIZE;
}

/**
 * returns information about the 2x1 piece to be build.
 * The lower bits (0-3) are the track type.
 */
static HighLightStyle Check2x1AutoRail(int mode)
{
	int fxpy = _tile_fract_coords.x + _tile_fract_coords.y;
	int sxpy = (_thd.selend.x & TILE_UNIT_MASK) + (_thd.selend.y & TILE_UNIT_MASK);
	int fxmy = _tile_fract_coords.x - _tile_fract_coords.y;
	int sxmy = (_thd.selend.x & TILE_UNIT_MASK) - (_thd.selend.y & TILE_UNIT_MASK);

	switch (mode) {
		default: NOT_REACHED();
		case 0: // end piece is lower right
			if (fxpy >= 20 && sxpy <= 12) return HT_DIR_HL;
			if (fxmy < -3 && sxmy > 3) return HT_DIR_VR;
			return HT_DIR_Y;

		case 1:
			if (fxmy > 3 && sxmy < -3) return HT_DIR_VL;
			if (fxpy <= 12 && sxpy >= 20) return HT_DIR_HU;
			return HT_DIR_Y;

		case 2:
			if (fxmy > 3 && sxmy < -3) return HT_DIR_VL;
			if (fxpy >= 20 && sxpy <= 12) return HT_DIR_HL;
			return HT_DIR_X;

		case 3:
			if (fxmy < -3 && sxmy > 3) return HT_DIR_VR;
			if (fxpy <= 12 && sxpy >= 20) return HT_DIR_HU;
			return HT_DIR_X;
	}
}

/**
 * Check if the direction of start and end tile should be swapped based on
 * the dragging-style. Default directions are:
 * in the case of a line (HT_RAIL, HT_LINE):  DIR_NE, DIR_NW, DIR_N, DIR_E
 * in the case of a rect (HT_RECT, HT_POINT): DIR_S, DIR_E
 * For example dragging a rectangle area from south to north should be swapped to
 * north-south (DIR_S) to obtain the same results with less code. This is what
 * the return value signifies.
 * @param style HighLightStyle dragging style
 * @param start_tile start tile of drag
 * @param end_tile end tile of drag
 * @return boolean value which when true means start/end should be swapped
 */
static bool SwapDirection(HighLightStyle style, TileIndex start_tile, TileIndex end_tile)
{
	uint start_x = TileX(start_tile);
	uint start_y = TileY(start_tile);
	uint end_x = TileX(end_tile);
	uint end_y = TileY(end_tile);

	switch (style & HT_DRAG_MASK) {
		case HT_RAIL:
		case HT_LINE: return (end_x > start_x || (end_x == start_x && end_y > start_y));

		case HT_RECT:
		case HT_POINT: return (end_x != start_x && end_y < start_y);
		default: NOT_REACHED();
	}

	return false;
}

/**
 * Calculates height difference between one tile and another.
 * Multiplies the result to suit the standard given by #TILE_HEIGHT_STEP.
 *
 * To correctly get the height difference we need the direction we are dragging
 * in, as well as with what kind of tool we are dragging. For example a horizontal
 * autorail tool that starts in bottom and ends at the top of a tile will need the
 * maximum of SW, S and SE, N corners respectively. This is handled by the lookup table below
 * See #_tileoffs_by_dir in map.cpp for the direction enums if you can't figure out the values yourself.
 * @param style      Highlighting style of the drag. This includes direction and style (autorail, rect, etc.)
 * @param distance   Number of tiles dragged, important for horizontal/vertical drags, ignored for others.
 * @param start_tile Start tile of the drag operation.
 * @param end_tile   End tile of the drag operation.
 * @return Height difference between two tiles. The tile measurement tool utilizes this value in its tooltip.
 */
static int CalcHeightdiff(HighLightStyle style, uint distance, TileIndex start_tile, TileIndex end_tile)
{
	bool swap = SwapDirection(style, start_tile, end_tile);
	uint h0, h1; // Start height and end height.

	if (start_tile == end_tile) return 0;
	if (swap) Swap(start_tile, end_tile);

	switch (style & HT_DRAG_MASK) {
		case HT_RECT: {
			static const TileIndexDiffC heightdiff_area_by_dir[] = {
				/* Start */ {1, 0}, /* Dragging east */ {0, 0}, // Dragging south
				/* End   */ {0, 1}, /* Dragging east */ {1, 1}  // Dragging south
			};

			/* In the case of an area we can determine whether we were dragging south or
			 * east by checking the X-coordinates of the tiles */
			byte style_t = (byte)(TileX(end_tile) > TileX(start_tile));
			start_tile = TILE_ADD(start_tile, ToTileIndexDiff(heightdiff_area_by_dir[style_t]));
			end_tile   = TILE_ADD(end_tile, ToTileIndexDiff(heightdiff_area_by_dir[2 + style_t]));
			FALLTHROUGH;
		}

		case HT_POINT:
			h0 = TileHeight(start_tile);
			h1 = TileHeight(end_tile);
			break;
		default: { // All other types, this is mostly only line/autorail
			static const HighLightStyle flip_style_direction[] = {
				HT_DIR_X, HT_DIR_Y, HT_DIR_HL, HT_DIR_HU, HT_DIR_VR, HT_DIR_VL
			};
			static const TileIndexDiffC heightdiff_line_by_dir[] = {
				/* Start */ {1, 0}, {1, 1}, /* HT_DIR_X  */ {0, 1}, {1, 1}, // HT_DIR_Y
				/* Start */ {1, 0}, {0, 0}, /* HT_DIR_HU */ {1, 0}, {1, 1}, // HT_DIR_HL
				/* Start */ {1, 0}, {1, 1}, /* HT_DIR_VL */ {0, 1}, {1, 1}, // HT_DIR_VR

				/* Start */ {0, 1}, {0, 0}, /* HT_DIR_X  */ {1, 0}, {0, 0}, // HT_DIR_Y
				/* End   */ {0, 1}, {0, 0}, /* HT_DIR_HU */ {1, 1}, {0, 1}, // HT_DIR_HL
				/* End   */ {1, 0}, {0, 0}, /* HT_DIR_VL */ {0, 0}, {0, 1}, // HT_DIR_VR
			};

			distance %= 2; // we're only interested if the distance is even or uneven
			style &= HT_DIR_MASK;

			/* To handle autorail, we do some magic to be able to use a lookup table.
			 * Firstly if we drag the other way around, we switch start&end, and if needed
			 * also flip the drag-position. Eg if it was on the left, and the distance is even
			 * that means the end, which is now the start is on the right */
			if (swap && distance == 0) style = flip_style_direction[style];

			/* Use lookup table for start-tile based on HighLightStyle direction */
			byte style_t = style * 2;
			assert(style_t < lengthof(heightdiff_line_by_dir) - 13);
			h0 = TileHeight(TILE_ADD(start_tile, ToTileIndexDiff(heightdiff_line_by_dir[style_t])));
			uint ht = TileHeight(TILE_ADD(start_tile, ToTileIndexDiff(heightdiff_line_by_dir[style_t + 1])));
			h0 = max(h0, ht);

			/* Use lookup table for end-tile based on HighLightStyle direction
			 * flip around side (lower/upper, left/right) based on distance */
			if (distance == 0) style_t = flip_style_direction[style] * 2;
			assert(style_t < lengthof(heightdiff_line_by_dir) - 13);
			h1 = TileHeight(TILE_ADD(end_tile, ToTileIndexDiff(heightdiff_line_by_dir[12 + style_t])));
			ht = TileHeight(TILE_ADD(end_tile, ToTileIndexDiff(heightdiff_line_by_dir[12 + style_t + 1])));
			h1 = max(h1, ht);
			break;
		}
	}

	if (swap) Swap(h0, h1);
	return (int)(h1 - h0) * TILE_HEIGHT_STEP;
}

static const StringID measure_strings_length[] = {STR_NULL, STR_MEASURE_LENGTH, STR_MEASURE_LENGTH_HEIGHTDIFF};

/**
 * Check for underflowing the map.
 * @param test  the variable to test for underflowing
 * @param other the other variable to update to keep the line
 * @param mult  the constant to multiply the difference by for \c other
 */
static void CheckUnderflow(int &test, int &other, int mult)
{
	if (test >= 0) return;

	other += mult * test;
	test = 0;
}

/**
 * Check for overflowing the map.
 * @param test  the variable to test for overflowing
 * @param other the other variable to update to keep the line
 * @param max   the maximum value for the \c test variable
 * @param mult  the constant to multiply the difference by for \c other
 */
static void CheckOverflow(int &test, int &other, int max, int mult)
{
	if (test <= max) return;

	other += mult * (test - max);
	test = max;
}

/** while dragging */
static void CalcRaildirsDrawstyle(int x, int y, int method)
{
	HighLightStyle b;

	int dx = _thd.selstart.x - (_thd.selend.x & ~TILE_UNIT_MASK);
	int dy = _thd.selstart.y - (_thd.selend.y & ~TILE_UNIT_MASK);
	uint w = abs(dx) + TILE_SIZE;
	uint h = abs(dy) + TILE_SIZE;

	if (method & ~(VPM_RAILDIRS | VPM_SIGNALDIRS)) {
		/* We 'force' a selection direction; first four rail buttons. */
		method &= ~(VPM_RAILDIRS | VPM_SIGNALDIRS);
		int raw_dx = _thd.selstart.x - _thd.selend.x;
		int raw_dy = _thd.selstart.y - _thd.selend.y;
		switch (method) {
			case VPM_FIX_X:
				b = HT_LINE | HT_DIR_Y;
				x = _thd.selstart.x;
				break;

			case VPM_FIX_Y:
				b = HT_LINE | HT_DIR_X;
				y = _thd.selstart.y;
				break;

			case VPM_FIX_HORIZONTAL:
				if (dx == -dy) {
					/* We are on a straight horizontal line. Determine the 'rail'
					 * to build based the sub tile location. */
					b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
				} else {
					/* We are not on a straight line. Determine the rail to build
					 * based on whether we are above or below it. */
					b = dx + dy >= (int)TILE_SIZE ? HT_LINE | HT_DIR_HU : HT_LINE | HT_DIR_HL;

					/* Calculate where a horizontal line through the start point and
					 * a vertical line from the selected end point intersect and
					 * use that point as the end point. */
					int offset = (raw_dx - raw_dy) / 2;
					x = _thd.selstart.x - (offset & ~TILE_UNIT_MASK);
					y = _thd.selstart.y + (offset & ~TILE_UNIT_MASK);

					/* 'Build' the last half rail tile if needed */
					if ((offset & TILE_UNIT_MASK) > (TILE_SIZE / 2)) {
						if (dx + dy >= (int)TILE_SIZE) {
							x += (dx + dy < 0) ? (int)TILE_SIZE : -(int)TILE_SIZE;
						} else {
							y += (dx + dy < 0) ? (int)TILE_SIZE : -(int)TILE_SIZE;
						}
					}

					/* Make sure we do not overflow the map! */
					CheckUnderflow(x, y, 1);
					CheckUnderflow(y, x, 1);
					CheckOverflow(x, y, (MapMaxX() - 1) * TILE_SIZE, 1);
					CheckOverflow(y, x, (MapMaxY() - 1) * TILE_SIZE, 1);
					assert(x >= 0 && y >= 0 && x <= (int)(MapMaxX() * TILE_SIZE) && y <= (int)(MapMaxY() * TILE_SIZE));
				}
				break;

			case VPM_FIX_VERTICAL:
				if (dx == dy) {
					/* We are on a straight vertical line. Determine the 'rail'
					 * to build based the sub tile location. */
					b = (x & TILE_UNIT_MASK) > (y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
				} else {
					/* We are not on a straight line. Determine the rail to build
					 * based on whether we are left or right from it. */
					b = dx < dy ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;

					/* Calculate where a vertical line through the start point and
					 * a horizontal line from the selected end point intersect and
					 * use that point as the end point. */
					int offset = (raw_dx + raw_dy + (int)TILE_SIZE) / 2;
					x = _thd.selstart.x - (offset & ~TILE_UNIT_MASK);
					y = _thd.selstart.y - (offset & ~TILE_UNIT_MASK);

					/* 'Build' the last half rail tile if needed */
					if ((offset & TILE_UNIT_MASK) > (TILE_SIZE / 2)) {
						if (dx - dy < 0) {
							y += (dx > dy) ? (int)TILE_SIZE : -(int)TILE_SIZE;
						} else {
							x += (dx < dy) ? (int)TILE_SIZE : -(int)TILE_SIZE;
						}
					}

					/* Make sure we do not overflow the map! */
					CheckUnderflow(x, y, -1);
					CheckUnderflow(y, x, -1);
					CheckOverflow(x, y, (MapMaxX() - 1) * TILE_SIZE, -1);
					CheckOverflow(y, x, (MapMaxY() - 1) * TILE_SIZE, -1);
					assert(x >= 0 && y >= 0 && x <= (int)(MapMaxX() * TILE_SIZE) && y <= (int)(MapMaxY() * TILE_SIZE));
				}
				break;

			default:
				NOT_REACHED();
		}
	} else if (TileVirtXY(_thd.selstart.x, _thd.selstart.y) == TileVirtXY(x, y)) { // check if we're only within one tile
		if (method & VPM_RAILDIRS) {
			b = GetAutorailHT(x, y);
		} else { // rect for autosignals on one tile
			b = HT_RECT;
		}
	} else if (h == TILE_SIZE) { // Is this in X direction?
		if (dx == (int)TILE_SIZE) { // 2x1 special handling
			b = (Check2x1AutoRail(3)) | HT_LINE;
		} else if (dx == -(int)TILE_SIZE) {
			b = (Check2x1AutoRail(2)) | HT_LINE;
		} else {
			b = HT_LINE | HT_DIR_X;
		}
		y = _thd.selstart.y;
	} else if (w == TILE_SIZE) { // Or Y direction?
		if (dy == (int)TILE_SIZE) { // 2x1 special handling
			b = (Check2x1AutoRail(1)) | HT_LINE;
		} else if (dy == -(int)TILE_SIZE) { // 2x1 other direction
			b = (Check2x1AutoRail(0)) | HT_LINE;
		} else {
			b = HT_LINE | HT_DIR_Y;
		}
		x = _thd.selstart.x;
	} else if (w > h * 2) { // still count as x dir?
		b = HT_LINE | HT_DIR_X;
		y = _thd.selstart.y;
	} else if (h > w * 2) { // still count as y dir?
		b = HT_LINE | HT_DIR_Y;
		x = _thd.selstart.x;
	} else { // complicated direction
		int d = w - h;
		_thd.selend.x = _thd.selend.x & ~TILE_UNIT_MASK;
		_thd.selend.y = _thd.selend.y & ~TILE_UNIT_MASK;

		/* four cases. */
		if (x > _thd.selstart.x) {
			if (y > _thd.selstart.y) {
				/* south */
				if (d == 0) {
					b = (x & TILE_UNIT_MASK) > (y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
				} else if (d >= 0) {
					x = _thd.selstart.x + h;
					b = HT_LINE | HT_DIR_VL;
				} else {
					y = _thd.selstart.y + w;
					b = HT_LINE | HT_DIR_VR;
				}
			} else {
				/* west */
				if (d == 0) {
					b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
				} else if (d >= 0) {
					x = _thd.selstart.x + h;
					b = HT_LINE | HT_DIR_HL;
				} else {
					y = _thd.selstart.y - w;
					b = HT_LINE | HT_DIR_HU;
				}
			}
		} else {
			if (y > _thd.selstart.y) {
				/* east */
				if (d == 0) {
					b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
				} else if (d >= 0) {
					x = _thd.selstart.x - h;
					b = HT_LINE | HT_DIR_HU;
				} else {
					y = _thd.selstart.y + w;
					b = HT_LINE | HT_DIR_HL;
				}
			} else {
				/* north */
				if (d == 0) {
					b = (x & TILE_UNIT_MASK) > (y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
				} else if (d >= 0) {
					x = _thd.selstart.x - h;
					b = HT_LINE | HT_DIR_VR;
				} else {
					y = _thd.selstart.y - w;
					b = HT_LINE | HT_DIR_VL;
				}
			}
		}
	}

	if (_settings_client.gui.measure_tooltip) {
		TileIndex t0 = TileVirtXY(_thd.selstart.x, _thd.selstart.y);
		TileIndex t1 = TileVirtXY(x, y);
		uint distance = DistanceManhattan(t0, t1) + 1;
		byte index = 0;
		uint64 params[2];

		if (distance != 1) {
			int heightdiff = CalcHeightdiff(b, distance, t0, t1);
			/* If we are showing a tooltip for horizontal or vertical drags,
			 * 2 tiles have a length of 1. To bias towards the ceiling we add
			 * one before division. It feels more natural to count 3 lengths as 2 */
			if ((b & HT_DIR_MASK) != HT_DIR_X && (b & HT_DIR_MASK) != HT_DIR_Y) {
				distance = CeilDiv(distance, 2);
			}

			params[index++] = distance;
			if (heightdiff != 0) params[index++] = heightdiff;
		}

		ShowMeasurementTooltips(measure_strings_length[index], index, params);
	}

	_thd.selend.x = x;
	_thd.selend.y = y;
	_thd.next_drawstyle = b;
}

/**
 * Selects tiles while dragging
 * @param x X coordinate of end of selection
 * @param y Y coordinate of end of selection
 * @param method modifies the way tiles are selected. Possible
 * methods are VPM_* in viewport.h
 */
void VpSelectTilesWithMethod(int x, int y, ViewportPlaceMethod method)
{
	int sx, sy;
	HighLightStyle style;

	if (x == -1) {
		_thd.selend.x = -1;
		return;
	}

	/* Special handling of drag in any (8-way) direction */
	if (method & (VPM_RAILDIRS | VPM_SIGNALDIRS)) {
		_thd.selend.x = x;
		_thd.selend.y = y;
		CalcRaildirsDrawstyle(x, y, method);
		return;
	}

	/* Needed so level-land is placed correctly */
	if ((_thd.next_drawstyle & HT_DRAG_MASK) == HT_POINT) {
		x += TILE_SIZE / 2;
		y += TILE_SIZE / 2;
	}

	sx = _thd.selstart.x;
	sy = _thd.selstart.y;

	int limit = 0;

	switch (method) {
		case VPM_X_OR_Y: // drag in X or Y direction
			if (abs(sy - y) < abs(sx - x)) {
				y = sy;
				style = HT_DIR_X;
			} else {
				x = sx;
				style = HT_DIR_Y;
			}
			goto calc_heightdiff_single_direction;

		case VPM_X_LIMITED: // Drag in X direction (limited size).
			limit = (_thd.sizelimit - 1) * TILE_SIZE;
			FALLTHROUGH;

		case VPM_FIX_X: // drag in Y direction
			x = sx;
			style = HT_DIR_Y;
			goto calc_heightdiff_single_direction;

		case VPM_Y_LIMITED: // Drag in Y direction (limited size).
			limit = (_thd.sizelimit - 1) * TILE_SIZE;
			FALLTHROUGH;

		case VPM_FIX_Y: // drag in X direction
			y = sy;
			style = HT_DIR_X;

calc_heightdiff_single_direction:;
			if (limit > 0) {
				x = sx + Clamp(x - sx, -limit, limit);
				y = sy + Clamp(y - sy, -limit, limit);
			}
			if (_settings_client.gui.measure_tooltip) {
				TileIndex t0 = TileVirtXY(sx, sy);
				TileIndex t1 = TileVirtXY(x, y);
				uint distance = DistanceManhattan(t0, t1) + 1;
				byte index = 0;
				uint64 params[2];

				if (distance != 1) {
					/* With current code passing a HT_LINE style to calculate the height
					 * difference is enough. However if/when a point-tool is created
					 * with this method, function should be called with new_style (below)
					 * instead of HT_LINE | style case HT_POINT is handled specially
					 * new_style := (_thd.next_drawstyle & HT_RECT) ? HT_LINE | style : _thd.next_drawstyle; */
					int heightdiff = CalcHeightdiff(HT_LINE | style, 0, t0, t1);

					params[index++] = distance;
					if (heightdiff != 0) params[index++] = heightdiff;
				}

				ShowMeasurementTooltips(measure_strings_length[index], index, params);
			}
			break;

		case VPM_X_AND_Y_LIMITED: // Drag an X by Y constrained rect area.
			limit = (_thd.sizelimit - 1) * TILE_SIZE;
			x = sx + Clamp(x - sx, -limit, limit);
			y = sy + Clamp(y - sy, -limit, limit);
			FALLTHROUGH;

		case VPM_X_AND_Y: // drag an X by Y area
			if (_settings_client.gui.measure_tooltip) {
				static const StringID measure_strings_area[] = {
					STR_NULL, STR_NULL, STR_MEASURE_AREA, STR_MEASURE_AREA_HEIGHTDIFF
				};

				TileIndex t0 = TileVirtXY(sx, sy);
				TileIndex t1 = TileVirtXY(x, y);
				uint dx = Delta(TileX(t0), TileX(t1)) + 1;
				uint dy = Delta(TileY(t0), TileY(t1)) + 1;
				byte index = 0;
				uint64 params[3];

				/* If dragging an area (eg dynamite tool) and it is actually a single
				 * row/column, change the type to 'line' to get proper calculation for height */
				style = (HighLightStyle)_thd.next_drawstyle;
				if (_thd.IsDraggingDiagonal()) {
					/* Determine the "area" of the diagonal dragged selection.
					 * We assume the area is the number of tiles along the X
					 * edge and the number of tiles along the Y edge. However,
					 * multiplying these two numbers does not give the exact
					 * number of tiles; basically we are counting the black
					 * squares on a chess board and ignore the white ones to
					 * make the tile counts at the edges match up. There is no
					 * other way to make a proper count though.
					 *
					 * First convert to the rotated coordinate system. */
					int dist_x = TileX(t0) - TileX(t1);
					int dist_y = TileY(t0) - TileY(t1);
					int a_max = dist_x + dist_y;
					int b_max = dist_y - dist_x;

					/* Now determine the size along the edge, but due to the
					 * chess board principle this counts double. */
					a_max = abs(a_max + (a_max > 0 ? 2 : -2)) / 2;
					b_max = abs(b_max + (b_max > 0 ? 2 : -2)) / 2;

					/* We get a 1x1 on normal 2x1 rectangles, due to it being
					 * a seen as two sides. As the result for actual building
					 * will be the same as non-diagonal dragging revert to that
					 * behaviour to give it a more normally looking size. */
					if (a_max != 1 || b_max != 1) {
						dx = a_max;
						dy = b_max;
					}
				} else if (style & HT_RECT) {
					if (dx == 1) {
						style = HT_LINE | HT_DIR_Y;
					} else if (dy == 1) {
						style = HT_LINE | HT_DIR_X;
					}
				}

				if (dx != 1 || dy != 1) {
					int heightdiff = CalcHeightdiff(style, 0, t0, t1);

					params[index++] = dx - (style & HT_POINT ? 1 : 0);
					params[index++] = dy - (style & HT_POINT ? 1 : 0);
					if (heightdiff != 0) params[index++] = heightdiff;
				}

				ShowMeasurementTooltips(measure_strings_area[index], index, params);
			}
			break;

		default: NOT_REACHED();
	}

	_thd.selend.x = x;
	_thd.selend.y = y;
}

/**
 * Handle the mouse while dragging for placement/resizing.
 * @return State of handling the event.
 */
EventState VpHandlePlaceSizingDrag()
{
	if (_special_mouse_mode != WSM_SIZING) return ES_NOT_HANDLED;

	/* stop drag mode if the window has been closed */
	Window *w = _thd.GetCallbackWnd();
	if (w == NULL) {
		ResetObjectToPlace();
		return ES_HANDLED;
	}

	/* while dragging execute the drag procedure of the corresponding window (mostly VpSelectTilesWithMethod() ) */
	if (_left_button_down) {
		w->OnPlaceDrag(_thd.select_method, _thd.select_proc, GetTileBelowCursor());
		return ES_HANDLED;
	}

	/* mouse button released..
	 * keep the selected tool, but reset it to the original mode. */
	_special_mouse_mode = WSM_NONE;
	HighLightStyle others = _thd.place_mode & ~(HT_DRAG_MASK | HT_DIR_MASK);
	if ((_thd.next_drawstyle & HT_DRAG_MASK) == HT_RECT) {
		_thd.place_mode = HT_RECT | others;
	} else if (_thd.select_method & VPM_SIGNALDIRS) {
		_thd.place_mode = HT_RECT | others;
	} else if (_thd.select_method & VPM_RAILDIRS) {
		_thd.place_mode = (_thd.select_method & ~VPM_RAILDIRS) ? _thd.next_drawstyle : (HT_RAIL | others);
	} else {
		_thd.place_mode = HT_POINT | others;
	}
	SetTileSelectSize(1, 1);

	w->OnPlaceMouseUp(_thd.select_method, _thd.select_proc, _thd.selend, TileVirtXY(_thd.selstart.x, _thd.selstart.y), TileVirtXY(_thd.selend.x, _thd.selend.y));

	return ES_HANDLED;
}

/**
 * Change the cursor and mouse click/drag handling to a mode for performing special operations like tile area selection, object placement, etc.
 * @param icon New shape of the mouse cursor.
 * @param pal Palette to use.
 * @param mode Mode to perform.
 * @param w %Window requesting the mode change.
 */
void SetObjectToPlaceWnd(CursorID icon, PaletteID pal, HighLightStyle mode, Window *w)
{
	SetObjectToPlace(icon, pal, mode, w->window_class, w->window_number);
}

#include "table/animcursors.h"

/**
 * Change the cursor and mouse click/drag handling to a mode for performing special operations like tile area selection, object placement, etc.
 * @param icon New shape of the mouse cursor.
 * @param pal Palette to use.
 * @param mode Mode to perform.
 * @param window_class %Window class of the window requesting the mode change.
 * @param window_num Number of the window in its class requesting the mode change.
 */
void SetObjectToPlace(CursorID icon, PaletteID pal, HighLightStyle mode, WindowClass window_class, WindowNumber window_num)
{
	if (_thd.window_class != WC_INVALID) {
		/* Undo clicking on button and drag & drop */
		Window *w = _thd.GetCallbackWnd();
		/* Call the abort function, but set the window class to something
		 * that will never be used to avoid infinite loops. Setting it to
		 * the 'next' window class must not be done because recursion into
		 * this function might in some cases reset the newly set object to
		 * place or not properly reset the original selection. */
		_thd.window_class = WC_INVALID;
		if (w != NULL) w->OnPlaceObjectAbort();
	}

	/* Mark the old selection dirty, in case the selection shape or colour changes */
	if ((_thd.drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();

	SetTileSelectSize(1, 1);

	_thd.make_square_red = false;

	if (mode == HT_DRAG) { // HT_DRAG is for dragdropping trains in the depot window
		mode = HT_NONE;
		_special_mouse_mode = WSM_DRAGDROP;
	} else {
		_special_mouse_mode = WSM_NONE;
	}

	_thd.place_mode = mode;
	_thd.window_class = window_class;
	_thd.window_number = window_num;

	if ((mode & HT_DRAG_MASK) == HT_SPECIAL) { // special tools, like tunnels or docks start with presizing mode
		VpStartPreSizing();
	}

	if ((icon & ANIMCURSOR_FLAG) != 0) {
		SetAnimatedMouseCursor(_animcursors[icon & ~ANIMCURSOR_FLAG]);
	} else {
		SetMouseCursor(icon, pal);
	}

}

/** Reset the cursor and mouse mode handling back to default (normal cursor, only clicking in windows). */
void ResetObjectToPlace()
{
	SetObjectToPlace(SPR_CURSOR_MOUSE, PAL_NONE, HT_NONE, WC_MAIN_WINDOW, 0);
}

Point GetViewportStationMiddle(const ViewPort *vp, const Station *st)
{
	int x = TileX(st->xy) * TILE_SIZE;
	int y = TileY(st->xy) * TILE_SIZE;
	int z = GetSlopePixelZ(Clamp(x, 0, MapSizeX() * TILE_SIZE - 1), Clamp(y, 0, MapSizeY() * TILE_SIZE - 1));

	Point p = RemapCoords(x, y, z);
	p.x = UnScaleByZoom(p.x - vp->virtual_left, vp->zoom) + vp->left;
	p.y = UnScaleByZoom(p.y - vp->virtual_top, vp->zoom) + vp->top;
	return p;
}

/** Helper class for getting the best sprite sorter. */
struct ViewportSSCSS {
	VpSorterChecker fct_checker; ///< The check function.
	VpSpriteSorter fct_sorter;   ///< The sorting function.
};

/** List of sorters ordered from best to worst. */
static ViewportSSCSS _vp_sprite_sorters[] = {
#ifdef WITH_SSE
	{ &ViewportSortParentSpritesSSE41Checker, &ViewportSortParentSpritesSSE41 },
#endif
	{ &ViewportSortParentSpritesChecker, &ViewportSortParentSprites }
};

/** Choose the "best" sprite sorter and set _vp_sprite_sorter. */
void InitializeSpriteSorter()
{
	for (uint i = 0; i < lengthof(_vp_sprite_sorters); i++) {
		if (_vp_sprite_sorters[i].fct_checker()) {
			_vp_sprite_sorter = _vp_sprite_sorters[i].fct_sorter;
			break;
		}
	}
	assert(_vp_sprite_sorter != NULL);
}

/**
 * Scroll players main viewport.
 * @param tile tile to center viewport on
 * @param flags type of operation
 * @param p1 ViewportScrollTarget of scroll target
 * @param p2 company or client id depending on the target
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdScrollViewport(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
	if (_current_company != OWNER_DEITY) return CMD_ERROR;
	ViewportScrollTarget target = (ViewportScrollTarget)p1;
	switch (target) {
		case VST_EVERYONE:
			break;
		case VST_COMPANY:
			if (_local_company != (CompanyID)p2) return CommandCost();
			break;
		case VST_CLIENT:
#ifdef ENABLE_NETWORK
			if (_network_own_client_id != (ClientID)p2) return CommandCost();
			break;
#else
			return CommandCost();
#endif
		default:
			return CMD_ERROR;
	}

	if (flags & DC_EXEC) {
		ResetObjectToPlace();
		ScrollMainWindowToTile(tile);
	}
	return CommandCost();
}