From ec2656ab7ef6d924f3c30624bf1d3c7449403c6f Mon Sep 17 00:00:00 2001
From: peter1138 <peter1138@openttd.org>
Date: Sat, 6 Apr 2019 23:33:09 +0100
Subject: [PATCH] Codechange: Restrict docking points of docks.

---
 src/ship_cmd.cpp    |  2 +-
 src/station_cmd.cpp | 22 ++++++++++++++++++++++
 src/station_func.h  |  1 +
 src/water_cmd.cpp   |  2 +-
 4 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/ship_cmd.cpp b/src/ship_cmd.cpp
index 73f2ee97f2..7b6be3a41a 100644
--- a/src/ship_cmd.cpp
+++ b/src/ship_cmd.cpp
@@ -612,7 +612,7 @@ bool IsShipDestinationTile(TileIndex tile, StationID station)
 	for (DiagDirection d = DIAGDIR_BEGIN; d != DIAGDIR_END; d++) {
 		TileIndex t = tile + TileOffsByDiagDir(d);
 		if (!IsValidTile(t)) continue;
-		if (IsDockTile(t) && GetStationIndex(t) == station) return true;
+		if (IsDockTile(t) && GetStationIndex(t) == station && IsValidDockingDirectionForDock(t, d)) return true;
 		if (IsTileType(t, MP_INDUSTRY)) {
 			const Industry *i = Industry::GetByTile(t);
 			if (i->neutral_station != nullptr && i->neutral_station->index == station) return true;
diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index a7d9866761..546aecc269 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -2631,6 +2631,28 @@ void ClearDockingTilesCheckingNeighbours(TileIndex tile)
 	}
 }
 
+/**
+ * Check if a dock tile can be docked from the given direction.
+ * @param t Tile index of dock.
+ * @param d DiagDirection adjacent to dock being tested.
+ * @return True iff the dock can be docked from the given direction.
+ */
+bool IsValidDockingDirectionForDock(TileIndex t, DiagDirection d)
+{
+	assert(IsDockTile(t));
+
+	/** Bitmap of valid directions for each dock tile part. */
+	static const uint8 _valid_docking_tile[] = {
+		0, 0, 0, 0,                        // No docking against the slope part.
+		1 << DIAGDIR_NE | 1 << DIAGDIR_SW, // Docking permitted at the end
+		1 << DIAGDIR_NW | 1 << DIAGDIR_SE, // of the flat piers.
+	};
+
+	StationGfx gfx = GetStationGfx(t);
+	assert(gfx < lengthof(_valid_docking_tile));
+	return HasBit(_valid_docking_tile[gfx], d);
+}
+
 /**
  * Find the part of a dock that is land-based
  * @param t Dock tile to find land part of
diff --git a/src/station_func.h b/src/station_func.h
index 44aec087fe..86aae1e56e 100644
--- a/src/station_func.h
+++ b/src/station_func.h
@@ -43,6 +43,7 @@ void DeleteOilRig(TileIndex t);
 void UpdateStationDockingTiles(Station *st);
 void RemoveDockingTile(TileIndex t);
 void ClearDockingTilesCheckingNeighbours(TileIndex tile);
+bool IsValidDockingDirectionForDock(TileIndex t, DiagDirection d);
 
 /* Check if a rail station tile is traversable. */
 bool IsStationTileBlocked(TileIndex tile);
diff --git a/src/water_cmd.cpp b/src/water_cmd.cpp
index 158bd13f03..7091f9f2d4 100644
--- a/src/water_cmd.cpp
+++ b/src/water_cmd.cpp
@@ -187,7 +187,7 @@ void CheckForDockingTile(TileIndex t)
 		TileIndex tile = t + TileOffsByDiagDir(d);
 		if (!IsValidTile(tile)) continue;
 
-		if (IsDockTile(tile)) {
+		if (IsDockTile(tile) && IsValidDockingDirectionForDock(tile, d)) {
 			Station::GetByTile(tile)->docking_station.Add(t);
 			SetDockingTile(t, true);
 		}