Chunnel: Prevent chunnels from intersecting with each other.

src/terraform_cmd.cpp

@@ -270,7 +270,7 @@ CommandCost CmdTerraformLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uin
 					}
 				}
 				/* Check if tunnel would take damage */
-				if (direction == -1 && IsTunnelInWay(tile, z_min, true)) {
+				if (direction == -1 && IsTunnelInWay(tile, z_min, ITIWF_IGNORE_CHUNNEL)) {
 					_terraform_err_tile = tile; // highlight the tile above the tunnel
 					return_cmd_error(STR_ERROR_EXCAVATION_WOULD_DAMAGE);
 				}

src/tunnel_map.cpp

@@ -103,14 +103,17 @@ TileIndex GetOtherTunnelEnd(TileIndex tile)
 	return t->tile_n == tile ? t->tile_s : t->tile_n;
 }
 
-static inline bool IsTunnelInWaySingleAxis(TileIndex tile, int z, bool chunnel_allowed, bool y_axis, TileIndexDiff tile_diff)
+static inline bool IsTunnelInWaySingleAxis(TileIndex tile, int z, IsTunnelInWayFlags flags, bool y_axis, TileIndexDiff tile_diff)
 {
 	const auto tunnels = tunnel_axis_height_index.equal_range(GetTunnelAxisHeightCacheKey(tile, z, y_axis));
 	for (auto it = tunnels.first; it != tunnels.second; ++it) {
 		const Tunnel *t = it->second;
 		if (t->tile_n > tile || tile > t->tile_s) continue;
 
-		if (t->is_chunnel && chunnel_allowed) {
+		if (!t->is_chunnel && (flags & ITIWF_CHUNNEL_ONLY)) {
+			continue;
+		}
+		if (t->is_chunnel && (flags & ITIWF_IGNORE_CHUNNEL)) {
 			/* Only if tunnel was built over water is terraforming is allowed between portals. */
 			const TileIndexDiff delta = tile_diff * 4;  // 4 tiles ramp.
 			if (tile < t->tile_n + delta || t->tile_s - delta < tile) return true;
@@ -128,7 +131,7 @@ static inline bool IsTunnelInWaySingleAxis(TileIndex tile, int z, bool chunnel_a
  * @param chunnel_allowed True if chunnel mid-parts are allowed, used when terraforming.
  * @return true if and only if there is a tunnel.
  */
-bool IsTunnelInWay(TileIndex tile, int z, bool chunnel_allowed)
+bool IsTunnelInWay(TileIndex tile, int z, IsTunnelInWayFlags flags)
 {
-	return IsTunnelInWaySingleAxis(tile, z, chunnel_allowed, false, 1) || IsTunnelInWaySingleAxis(tile, z, chunnel_allowed, true, TileOffsByDiagDir(DIAGDIR_SE));
+	return IsTunnelInWaySingleAxis(tile, z, flags, false, 1) || IsTunnelInWaySingleAxis(tile, z, flags, true, TileOffsByDiagDir(DIAGDIR_SE));
 }

src/tunnel_map.h

@@ -56,7 +56,16 @@ static inline TunnelID GetTunnelIndex(TileIndex t)
 }
 
 TileIndex GetOtherTunnelEnd(TileIndex);
-bool IsTunnelInWay(TileIndex, int z, bool chunnel_allowed = false);
+
+/** Flags for miscellaneous industry tile specialities */
+enum IsTunnelInWayFlags {
+	ITIWF_NONE                  = 0,
+	ITIWF_IGNORE_CHUNNEL        = 1 << 0, ///< Chunnel mid-parts are ignored, used when terraforming.
+	ITIWF_CHUNNEL_ONLY          = 1 << 1, ///< Only check for chunnels
+};
+DECLARE_ENUM_AS_BIT_SET(IsTunnelInWayFlags)
+
+bool IsTunnelInWay(TileIndex, int z, IsTunnelInWayFlags flags = ITIWF_NONE);
 
 /**
  * Set the index of tunnel tile.

src/tunnelbridge_cmd.cpp

@@ -740,7 +740,7 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 			head_tiles = 0;
 			found_tunnel_tile = INVALID_TILE;
 		}
-		if (!_cheats.crossing_tunnels.value && IsTunnelInWay(end_tile, start_z, true)) {
+		if (!_cheats.crossing_tunnels.value && IsTunnelInWay(end_tile, start_z, ITIWF_IGNORE_CHUNNEL)) {
 			if (found_tunnel_tile == INVALID_TILE || is_chunnel) { // Remember the first or the last when we pass a tunnel.
 				found_tunnel_tile = end_tile;
 				head_tiles = 0;
@@ -749,6 +749,26 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 		head_tiles++;
 		tiles++;
 	}
+
+	if (is_chunnel && !_cheats.crossing_tunnels.value) {
+		/*
+		 * Chunnel check: second pass
+		 *
+		 * Make sure that we don't intersect with any other chunnels
+		 */
+
+		TileIndex check_tile = start_tile;
+		for (;;) {
+			check_tile += delta;
+			if (check_tile == end_tile) break;
+
+			if (IsTunnelInWay(check_tile, start_z, ITIWF_CHUNNEL_ONLY)) {
+				_build_tunnel_endtile = check_tile;
+				return_cmd_error(STR_ERROR_ANOTHER_TUNNEL_IN_THE_WAY);
+			}
+		}
+	}
+
 	/* The cost of the digging. */
 	for (int i = tiles; i > 0; i--) {
 		if (tiles == tiles_bump) {