From aa9f44eaec14f7acbe731dbe8f469f464d94c459 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Sun, 1 Nov 2015 21:51:10 +0000
Subject: [PATCH] Fix flicker/render errors of bridge/tunnels in viewport map
 mode.

Fix bridges not being rendered when the region to be repainted
did not intersect with either of the bridge ends.
Fix flicker due to non-deterministic ordering of the two bridge/tunnel
ends (if the tile heights of the two ends are different).
---
 src/viewport.cpp | 42 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/src/viewport.cpp b/src/viewport.cpp
index d478c7f753..95574a3df0 100644
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -1545,8 +1545,17 @@ static void ViewportMapStoreBridgeTunnel(const ViewPort * const vp, const TileIn
 
 	/* It's a new one, add it to the list */
 	tbtm = tbtmv->Append();
-	tbtm->from_tile = tile;
-	tbtm->to_tile = GetOtherTunnelBridgeEnd(tile);
+	TileIndex other_end = GetOtherTunnelBridgeEnd(tile);
+
+	/* ensure deterministic ordering, to avoid render flicker */
+	if (other_end > tile) {
+		tbtm->from_tile = other_end;
+		tbtm->to_tile = tile;
+	} else {
+		tbtm->from_tile = tile;
+		tbtm->to_tile = other_end;
+	}
+
 	if (vp->map_type == VPMT_OWNER && _settings_client.gui.use_owner_colour_for_tunnelbridge && o < MAX_COMPANIES) {
 		const uint8 colour = _legend_land_owners[_company_to_list_pos[o]].colour;
 		tbtm->colour = tile_is_tunnel ? _darken_colour[colour] : _lighten_colour[colour];
@@ -2083,6 +2092,31 @@ static inline uint32 ViewportMapGetColourOwner(const TileIndex tile, TileType t,
 	return colour;
 }
 
+static inline void ViewportMapStoreBridgeAboveTile(const ViewPort * const vp, const TileIndex tile)
+{
+	/* No need to bother for hidden things */
+	if (!_settings_client.gui.show_bridges_on_map) return;
+
+	/* Check existing stored bridges */
+	TunnelBridgeToMap *tbtm = _vd.tunnel_bridge_to_map.Begin();
+	TunnelBridgeToMap *tbtm_end = _vd.tunnel_bridge_to_map.End();
+	for (; tbtm != tbtm_end; ++tbtm) {
+		if (!IsBridge(tbtm->from_tile)) continue;
+
+		TileIndex from = tbtm->from_tile;
+		TileIndex to = tbtm->to_tile;
+		if (TileX(from) == TileX(to) && TileX(from) == TileX(tile)) {
+			if (TileY(from) > TileY(to)) std::swap(from, to);
+			if (TileY(from) <= TileY(tile) && TileY(tile) <= TileY(to)) return; /* already covered */
+		} else if (TileY(from) == TileY(to) && TileY(from) == TileY(tile)) {
+			if (TileX(from) > TileX(to)) std::swap(from, to);
+			if (TileX(from) <= TileX(tile) && TileX(tile) <= TileX(to)) return; /* already covered */
+		}
+	}
+
+	ViewportMapStoreBridgeTunnel(vp, GetSouthernBridgeEnd(tile));
+}
+
 static inline TileIndex ViewportMapGetMostSignificantTileType(const ViewPort * const vp, const TileIndex from_tile, TileType * const tile_type)
 {
 	if (vp->zoom <= ZOOM_LVL_OUT_128X || !_settings_client.gui.viewport_map_scan_surroundings) {
@@ -2090,6 +2124,7 @@ static inline TileIndex ViewportMapGetMostSignificantTileType(const ViewPort * c
 		/* Store bridges and tunnels. */
 		if (ttype != MP_TUNNELBRIDGE) {
 			*tile_type = ttype;
+			if (IsBridgeAbove(from_tile)) ViewportMapStoreBridgeAboveTile(vp, from_tile);
 		} else {
 			ViewportMapStoreBridgeTunnel(vp, from_tile);
 			switch (GetTunnelBridgeTransportType(from_tile)) {
@@ -2116,6 +2151,9 @@ static inline TileIndex ViewportMapGetMostSignificantTileType(const ViewPort * c
 			importance = tile_importance;
 			result = tile;
 		}
+		if (ttype != MP_TUNNELBRIDGE && IsBridgeAbove(tile)) {
+			ViewportMapStoreBridgeAboveTile(vp, tile);
+		}
 	}
 
 	/* Store bridges and tunnels. */