1 files changed, 51 insertions, 0 deletions
diff --git a/src/landscape.cpp b/src/landscape.cpp
index 18f27807d..eb1e404f0 100644
--- a/src/landscape.cpp
+++ b/src/landscape.cpp
@@ -90,6 +90,57 @@ extern const byte _slope_to_sprite_offset[32] = {
 static SnowLine *_snow_line = NULL;
 
 /**
+ * Map 2D viewport or smallmap coordinate to 3D world or tile coordinate.
+ * Function takes into account height of tiles and foundations.
+ *
+ * @param x X viewport 2D coordinate.
+ * @param y Y viewport 2D coordinate.
+ * @param clamp_to_map Clamp the coordinate outside of the map to the closest, non-void tile within the map.
+ * @return 3D world coordinate of point visible at the given screen coordinate (3D perspective).
+ *
+ * @note Inverse of #RemapCoords2 function. Smaller values may get rounded.
+ * @see InverseRemapCoords
+ */
+Point InverseRemapCoords2(int x, int y, bool clamp_to_map)
+{
+	/* Initial x/y world coordinate is like if the landscape
+	 * was completely flat on height 0. */
+	Point pt = InverseRemapCoords(x, y);
+
+	const uint min_coord = _settings_game.construction.freeform_edges ? TILE_SIZE : 0;
+	const uint max_x = MapMaxX() * TILE_SIZE - 1;
+	const uint max_y = MapMaxY() * TILE_SIZE - 1;
+
+	if (clamp_to_map) {
+		/* Bring the coordinates near to a valid range. At the top we allow a number
+		 * of extra tiles. This is mostly due to the tiles on the north side of
+		 * the map possibly being drawn higher due to the extra height levels. */
+		int extra_tiles = CeilDiv(_settings_game.construction.max_heightlevel * TILE_HEIGHT, TILE_PIXELS);
+		pt.x = Clamp(pt.x, -extra_tiles * TILE_SIZE, max_x);
+		pt.y = Clamp(pt.y, -extra_tiles * TILE_SIZE, max_y);
+	}
+
+	/* 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. */
+	int z = 0;
+	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(pt.x + max(z, 4) - 4, min_coord, max_x), Clamp(pt.y + max(z, 4) - 4, min_coord, max_y)) / 2;
+	for (int m = 3; m > 0; m--) z = GetSlopePixelZ(Clamp(pt.x + max(z, m) - m, min_coord, max_x), Clamp(pt.y + max(z, m) - m, min_coord, max_y)) / 2;
+	for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(pt.x + z,             min_coord, max_x), Clamp(pt.y + z,             min_coord, max_y)) / 2;
+
+	pt.x += z;
+	pt.y += z;
+	if (clamp_to_map) {
+		pt.x = Clamp(pt.x, min_coord, max_x);
+		pt.y = Clamp(pt.y, min_coord, max_y);
+	}
+
+	return pt;
+}
+
+/**
  * Applies a foundation to a slope.
  *
  * @pre      Foundation and slope must be valid combined.