Feature: Press ctrl to build diagonal rivers in Scenario Editor (#8880)

3 files changed, 20 insertions, 8 deletions

diff --git a/src/dock_gui.cpp b/src/dock_gui.cpp
index d676bf8b9..850b9d3f3 100644
--- a/src/dock_gui.cpp
+++ b/src/dock_gui.cpp
@@ -170,7 +170,7 @@ struct BuildDocksToolbarWindow : Window {
 
 			case WID_DT_RIVER: // Build river button (in scenario editor)
 				if (_game_mode != GM_EDITOR) return;
-				HandlePlacePushButton(this, WID_DT_RIVER, SPR_CURSOR_RIVER, HT_RECT);
+				HandlePlacePushButton(this, WID_DT_RIVER, SPR_CURSOR_RIVER, HT_RECT | HT_DIAGONAL);
 				break;
 
 			case WID_DT_BUILD_AQUEDUCT: // Build aqueduct button
@@ -247,7 +247,7 @@ struct BuildDocksToolbarWindow : Window {
 					DoCommandP(end_tile, start_tile, (_game_mode == GM_EDITOR && _ctrl_pressed) ? WATER_CLASS_SEA : WATER_CLASS_CANAL, CMD_BUILD_CANAL | CMD_MSG(STR_ERROR_CAN_T_BUILD_CANALS), CcPlaySound_CONSTRUCTION_WATER);
 					break;
 				case DDSP_CREATE_RIVER:
-					DoCommandP(end_tile, start_tile, WATER_CLASS_RIVER, CMD_BUILD_CANAL | CMD_MSG(STR_ERROR_CAN_T_PLACE_RIVERS), CcPlaySound_CONSTRUCTION_WATER);
+					DoCommandP(end_tile, start_tile, WATER_CLASS_RIVER | (_ctrl_pressed ? 1 << 2 : 0), CMD_BUILD_CANAL | CMD_MSG(STR_ERROR_CAN_T_PLACE_RIVERS), CcPlaySound_CONSTRUCTION_WATER);
 					break;
 
 				default: break;
diff --git a/src/lang/english.txt b/src/lang/english.txt
index 9f43788e5..e55fcba1a 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -2531,7 +2531,7 @@ STR_WATERWAYS_TOOLBAR_BUILD_DOCK_TOOLTIP                        :{BLACK}Build sh
 STR_WATERWAYS_TOOLBAR_BUOY_TOOLTIP                              :{BLACK}Place a buoy which can be used as a waypoint. Shift toggles building/showing cost estimate
 STR_WATERWAYS_TOOLBAR_BUILD_AQUEDUCT_TOOLTIP                    :{BLACK}Build aqueduct. Shift toggles building/showing cost estimate
 STR_WATERWAYS_TOOLBAR_CREATE_LAKE_TOOLTIP                       :{BLACK}Define water area.{}Make a canal, unless Ctrl is held down at sea level, when it will flood the surroundings instead
-STR_WATERWAYS_TOOLBAR_CREATE_RIVER_TOOLTIP                      :{BLACK}Place rivers
+STR_WATERWAYS_TOOLBAR_CREATE_RIVER_TOOLTIP                      :{BLACK}Place rivers. Ctrl selects the area diagonally
 
 # Ship depot construction window
 STR_DEPOT_BUILD_SHIP_CAPTION                                    :{WHITE}Ship Depot Orientation
diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
index 6a3b73065..731954c2e 100644
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -437,7 +437,9 @@ bool RiverModifyDesertZone(TileIndex tile, void *)
  * @param tile end tile of stretch-dragging
  * @param flags type of operation
  * @param p1 start tile of stretch-dragging
- * @param p2 waterclass to build. sea and river can only be built in scenario editor
+ * @param p2 various bitstuffed data
+ *  bits  0-1: waterclass to build. sea and river can only be built in scenario editor
+ *  bit     2: Whether to use the Orthogonal (0) or Diagonal (1) iterator.
  * @param text unused
  * @return the cost of this operation or an error
  */
@@ -449,13 +451,23 @@ CommandCost CmdBuildCanal(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 	/* Outside of the editor you can only build canals, not oceans */
 	if (wc != WATER_CLASS_CANAL && _game_mode != GM_EDITOR) return CMD_ERROR;
 
-	TileArea ta(tile, p1);
-
 	/* Outside the editor you can only drag canals, and not areas */
-	if (_game_mode != GM_EDITOR && ta.w != 1 && ta.h != 1) return CMD_ERROR;
+	if (_game_mode != GM_EDITOR) {
+		TileArea ta(tile, p1);
+		if (ta.w != 1 && ta.h != 1) return CMD_ERROR;
+	}
 
 	CommandCost cost(EXPENSES_CONSTRUCTION);
-	TILE_AREA_LOOP(tile, ta) {
+
+	std::unique_ptr<TileIterator> iter;
+	if (HasBit(p2, 2)) {
+		iter = std::make_unique<DiagonalTileIterator>(tile, p1);
+	} else {
+		iter = std::make_unique<OrthogonalTileIterator>(tile, p1);
+	}
+
+	for (; *iter != INVALID_TILE; ++(*iter)) {
+		TileIndex tile = *iter;
 		CommandCost ret;
 
 		Slope slope = GetTileSlope(tile);