Chunnel patch 28396: Codechange: Chunnel portal must have minimal length of 4 tiles.

https://www.tt-forums.net/viewtopic.php?p=1183416#p1183416

src/lang/english.txt

@@ -5002,6 +5002,7 @@ STR_ERROR_ANOTHER_TUNNEL_IN_THE_WAY                             :{WHITE}Another
 STR_ERROR_TUNNEL_THROUGH_MAP_BORDER                             :{WHITE}Tunnel would end out of the map
 STR_ERROR_UNABLE_TO_EXCAVATE_LAND                               :{WHITE}Unable to excavate land for other end of tunnel
 STR_ERROR_TUNNEL_TOO_LONG                                       :{WHITE}... tunnel too long
+STR_ERROR_TUNNEL_RAMP_TOO_SHORT                                 :{WHITE}... Ramp too short, tunnels under water have minimal three tiles at the begin and end.
 
 # Object related errors
 STR_ERROR_TOO_MANY_OBJECTS                                      :{WHITE}... too many objects

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)) {
+				if (direction == -1 && IsTunnelInWay(tile, z_min, false)) {
 					_terraform_err_tile = tile; // highlight the tile above the tunnel
 					return_cmd_error(STR_ERROR_EXCAVATION_WOULD_DAMAGE);
 				}

src/tunnel_base.h

@@ -24,6 +24,7 @@ struct Tunnel : TunnelPool::PoolItem<&_tunnel_pool> {
 
 	TileIndex tile_n; // North tile of tunnel.
 	TileIndex tile_s; // South tile of tunnel.
+	bool is_chunnel;
 
 	Tunnel(TileIndex tile_n = INVALID_TILE) : tile_n(tile_n) {}
 	~Tunnel();

src/tunnel_map.cpp

@@ -44,9 +44,10 @@ TileIndex GetOtherTunnelEnd(TileIndex tile)
  * Is there a tunnel in the way in any direction?
  * @param tile the tile to search from.
  * @param z the 'z' to search on.
+ * @param not_allowed Only terra forming does not search between tunnel portals.
  * @return true if and only if there is a tunnel.
  */
-bool IsTunnelInWay(TileIndex tile, int z)
+bool IsTunnelInWay(TileIndex tile, int z, bool not_allowed)
 {
 	uint x = TileX(tile);
 	uint y = TileY(tile);
@@ -61,6 +62,12 @@ bool IsTunnelInWay(TileIndex tile, int z)
 			if (TileY(t->tile_n) != y || (int)TileHeight(t->tile_n) != z) continue; // dir DIAGDIR_SW
 		}
 
+		if (t->is_chunnel > not_allowed) {
+			/* Only if tunnel was build over water terraforming is allowed between portals. */
+			TileIndexDiff delta = GetTunnelBridgeDirection(t->tile_n) == DIAGDIR_SE ? TileOffsByDiagDir(DIAGDIR_SE) * 4 : 4;  // 4 tiles ramp.
+			if (tile < t->tile_n + delta || t->tile_s - delta < tile) return true;
+			continue;
+		}
 		return true;
 	}
 	return false;

src/tunnel_map.h

@@ -51,7 +51,7 @@ static inline TunnelID GetTunnelIndex(TileIndex t)
 }
 
 TileIndex GetOtherTunnelEnd(TileIndex);
-bool IsTunnelInWay(TileIndex, int z);
+bool IsTunnelInWay(TileIndex, int z, bool not_allowed = true);
 
 /**
  * Makes a road tunnel entrance

src/tunnelbridge_cmd.cpp

@@ -670,6 +670,10 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 	int tiles_coef = 3;
 	/* Number of tiles from start of tunnel */
 	int tiles = 0;
+	/* flag for chunnels. */
+	bool is_chunnel = false;
+	/* Number of chunnel head tiles. */
+	int head_tiles = 1;
 	/* Number of tiles at which the cost increase coefficient per tile is halved */
 	int tiles_bump = 25;
 
@@ -691,6 +695,9 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 
 			/* A shore was found so pass the water and find a proper shore tile that potentially
 			 * could have a tunnel portal behind. */
+			is_chunnel = true;
+			if (head_tiles < 4 && is_chunnel) break; // Not enough lead way to go under water.
+			head_tiles = 0;
 			for (;;) {
 				if (!IsValidTile(end_tile)) return_cmd_error(STR_ERROR_TUNNEL_THROUGH_MAP_BORDER);
 
@@ -704,10 +711,10 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 				tiles++;
 			}
 		}
-		if (!_cheats.crossing_tunnels.value && IsTunnelInWay(end_tile, start_z)) {
+		if (!_cheats.crossing_tunnels.value && IsTunnelInWay(end_tile, start_z, false)) {
 			return_cmd_error(STR_ERROR_ANOTHER_TUNNEL_IN_THE_WAY);
 		}
-
+		head_tiles++;
 		tiles++;
 	}
 	/* The cost of the digging. */
@@ -730,6 +737,8 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 
 	if (tiles > _settings_game.construction.max_tunnel_length) return_cmd_error(STR_ERROR_TUNNEL_TOO_LONG);
 
+	if (head_tiles < 4 && is_chunnel) return_cmd_error(STR_ERROR_TUNNEL_RAMP_TOO_SHORT);
+
 	if (HasTileWaterGround(end_tile)) return_cmd_error(STR_ERROR_CAN_T_BUILD_ON_WATER);
 
 	/* Clear the tile in any case */
@@ -777,6 +786,7 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 		if (!Tunnel::CanAllocateItem()) return CMD_ERROR;
 		Tunnel *t = new Tunnel(tn);
 		t->tile_s = ts;
+		t->is_chunnel = is_chunnel;
 
 		if (transport_type == TRANSPORT_RAIL) {
 			if (!IsTunnelTile(start_tile) && c != NULL) c->infrastructure.rail[railtype] += num_pieces;