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-rw-r--r--src/tile_map.cpp45
1 files changed, 25 insertions, 20 deletions
diff --git a/src/tile_map.cpp b/src/tile_map.cpp
index 27b0a08a1..4f6ea17d6 100644
--- a/src/tile_map.cpp
+++ b/src/tile_map.cpp
@@ -14,13 +14,6 @@
* @return Slope of the tile, except for the HALFTILE part */
Slope GetTileSlope(TileIndex tile, uint *h)
{
- uint a;
- uint b;
- uint c;
- uint d;
- uint min;
- uint r;
-
assert(tile < MapSize());
if (TileX(tile) == MapMaxX() || TileY(tile) == MapMaxY()) {
@@ -28,15 +21,27 @@ Slope GetTileSlope(TileIndex tile, uint *h)
return SLOPE_FLAT;
}
- min = a = TileHeight(tile);
- b = TileHeight(tile + TileDiffXY(1, 0));
+ uint a = TileHeight(tile); // Height of the N corner
+ uint min = a; // Minimal height of all corners examined so far
+ uint b = TileHeight(tile + TileDiffXY(1, 0)); // Height of the W corner
if (min > b) min = b;
- c = TileHeight(tile + TileDiffXY(0, 1));
+ uint c = TileHeight(tile + TileDiffXY(0, 1)); // Height of the E corner
if (min > c) min = c;
- d = TileHeight(tile + TileDiffXY(1, 1));
+ uint d = TileHeight(tile + TileDiffXY(1, 1)); // Height of the S corner
if (min > d) min = d;
- r = SLOPE_FLAT;
+ /* Due to the fact that tiles must connect with each other without leaving gaps, the
+ * biggest difference in height between any corner and 'min' is between 0, 1, or 2.
+ *
+ * Also, there is at most 1 corner with height difference of 2.
+ */
+
+ uint r = SLOPE_FLAT; // Computed slope of the tile
+
+ /* For each corner if not equal to minimum height:
+ * - set the SLOPE_STEEP flag if the difference is 2
+ * - add the corresponding SLOPE_X constant to the computed slope
+ */
if ((a -= min) != 0) r += (--a << 4) + SLOPE_N;
if ((c -= min) != 0) r += (--c << 4) + SLOPE_E;
if ((d -= min) != 0) r += (--d << 4) + SLOPE_S;
@@ -55,10 +60,10 @@ uint GetTileZ(TileIndex tile)
{
if (TileX(tile) == MapMaxX() || TileY(tile) == MapMaxY()) return 0;
- uint h = TileHeight(tile);
- h = min(h, TileHeight(tile + TileDiffXY(1, 0)));
- h = min(h, TileHeight(tile + TileDiffXY(0, 1)));
- h = min(h, TileHeight(tile + TileDiffXY(1, 1)));
+ uint h = TileHeight(tile); // N corner
+ h = min(h, TileHeight(tile + TileDiffXY(1, 0))); // W corner
+ h = min(h, TileHeight(tile + TileDiffXY(0, 1))); // E corner
+ h = min(h, TileHeight(tile + TileDiffXY(1, 1))); // S corner
return h * TILE_HEIGHT;
}
@@ -71,10 +76,10 @@ uint GetTileMaxZ(TileIndex t)
{
if (TileX(t) == MapMaxX() || TileY(t) == MapMaxY()) return 0;
- uint h = TileHeight(t);
- h = max(h, TileHeight(t + TileDiffXY(1, 0)));
- h = max(h, TileHeight(t + TileDiffXY(0, 1)));
- h = max(h, TileHeight(t + TileDiffXY(1, 1)));
+ uint h = TileHeight(t); // N corner
+ h = max(h, TileHeight(t + TileDiffXY(1, 0))); // W corner
+ h = max(h, TileHeight(t + TileDiffXY(0, 1))); // E corner
+ h = max(h, TileHeight(t + TileDiffXY(1, 1))); // S corner
return h * TILE_HEIGHT;
}