(svn r21314) -Fix [FS#4253]: [NewGRF] (Hopefully) make callback 157 behave more like TTDPatch does, i.e. fall back to the default check when the callback is not yielding a result for a tile instead of disallowing building the object

1 files changed, 11 insertions, 9 deletions

diff --git a/src/object_cmd.cpp b/src/object_cmd.cpp
index eab4ac075..8958a714a 100644
--- a/src/object_cmd.cpp
+++ b/src/object_cmd.cpp
@@ -202,18 +202,20 @@ CommandCost CmdBuildObject(TileIndex tile, DoCommandFlag flags, uint32 p1, uint3
 		}
 
 		/* So, now the surface is checked... check the slope of said surface. */
-		if (HasBit(spec->callback_mask, CBM_OBJ_SLOPE_CHECK)) {
-			TILE_AREA_LOOP(t, ta) {
+		int allowed_z;
+		if (GetTileSlope(tile, (uint*)&allowed_z) != SLOPE_FLAT) allowed_z += TILE_HEIGHT;
+
+		TILE_AREA_LOOP(t, ta) {
+			uint16 callback = CALLBACK_FAILED;
+			if (HasBit(spec->callback_mask, CBM_OBJ_SLOPE_CHECK)) {
 				TileIndex diff = t - tile;
-				uint16 callback = GetObjectCallback(CBID_OBJECT_LAND_SLOPE_CHECK, GetTileSlope(t, NULL), TileY(diff) << 4 | TileX(diff), spec, NULL, t);
-				if (callback != 0) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
+				callback = GetObjectCallback(CBID_OBJECT_LAND_SLOPE_CHECK, GetTileSlope(t, NULL), TileY(diff) << 4 | TileX(diff), spec, NULL, t);
 			}
-		} else {
-			/* Check whether the ground is flat enough. */
-			int allowed_z = -1;
-			TILE_AREA_LOOP(t, ta) {
-				/* We'll do the bridge test later; it's quite custom. */
+
+			if (callback == CALLBACK_FAILED) {
 				cost.AddCost(CheckBuildableTile(t, 0, allowed_z, false));
+			} else if (callback != 0) {
+				return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
 			}
 		}
 	}