Fix building placement, and filter flags for building placement

src/include/map.h

@@ -364,6 +364,8 @@ extern  void MarkDrawEntireMap(void);
 //
 // in map_fog.c
 //
+	/// Filter map flags through fog
+extern int MapFogFilterFlags(Player* player, int x, int y, int mask);
 	/// Mark a tile for normal sight
 extern void MapMarkTileSight(const Player* player, int x, int y);
 	/// Unmark a tile for normal sight

src/map/map_fog.cpp

@@ -225,6 +225,36 @@ global unsigned char IsTileVisible(const Player* player, int x, int y)
 	return 0;
 }
 
+/**
+**  Find out what the tile flags are a tile is covered by fog
+**
+**  @param player  player who is doing operation
+**  @param x       X map location
+**  @param y       Y map location
+**  @param mask    input mask to filter
+**
+**  @return        Filtered mask after taking fog into account
+*/
+global int MapFogFilterFlags(Player* player, int x, int y, int mask)
+{
+	int nunits;
+	int unitcount;
+	int fogmask;
+	Unit* table[UnitMax];
+	
+			// Calculate Mask for tile with fog
+			nunits = UnitCacheOnTile(x, y, table);
+			fogmask = -1;
+			unitcount = 0;
+			while (unitcount < nunits) {
+				if (!UnitVisibleAsGoal(table[unitcount], player)) {
+					fogmask &= ~table[unitcount]->Type->FieldFlags;
+				}
+				++unitcount;
+			}
+	return mask & fogmask;
+}
+
 /**
 **		Mark a tile's sight. (Explore and make visible.)
 **

src/ui/mouse.cpp

@@ -124,7 +124,7 @@ global void DoRightButton(int sx, int sy)
 	// Unit selected isn't owned by the player.
 	// You can't select your own units + foreign unit(s).
 	//
-	if (!CanSelectMultipleUnits(Selected[0]->Player)) {
+	if (!CanSelectMultipleUnits(Selected[0]->Player) && 0) {
 		return;
 	}
 
@@ -1448,7 +1448,7 @@ global void UIHandleButtonDown(unsigned button)
 					}
 				}
 				if (CanBuildUnitTypeMask(Selected[0], CursorBuilding, x, y,
-					Selected[0]->Type->MovementMask & ~(MapFieldBuilding | MapFieldLandUnit | MapFieldSeaUnit)) &&
+					Selected[0]->Type->MovementMask) &&
 						(explored || ReplayRevealMap)) {
 					PlayGameSound(GameSounds.PlacementSuccess.Sound,
 						MaxSampleVolume);

src/unit/unit.cpp

@@ -2106,6 +2106,7 @@ global int CanBuildUnitTypeMask(const Unit* unit, const UnitType* type, int x, i
 	int w;
 	int h;
 	int j;
+	int testmask;
 	Player* player;
 
 	// Terrain Flags don't matter.
@@ -2209,7 +2210,12 @@ global int CanBuildUnitTypeMask(const Unit* unit, const UnitType* type, int x, i
 
 	for (h = type->TileHeight; h--;) {
 		for (w = type->TileWidth; w--;) {
-			if (!CanBuildOn(x + w, y + h, mask)) {
+			if (player) {
+				testmask = MapFogFilterFlags(player, x + w, y + h, mask);
+			} else {
+				testmask = mask;
+			}
+			if (!CanBuildOn(x + w, y + h, testmask)) {
 				if (unit) {
 					TheMap.Fields[unit->X + unit->Y * TheMap.Width].Flags |= j;
 				}

src/video/cursor.cpp

@@ -545,14 +545,11 @@ local void DrawBuildingCursor(void)
 	while (h--) {
 		w = w0;
 		while (w--) {
-
 			if (f && (CursorBuilding->MustBuildOnTop ||
-					CanBuildOn(mx + w, my + h, mask & ((NumSelected &&
-						!CursorBuilding->BuilderOutside &&
+					CanBuildOn(mx + w, my + h, MapFogFilterFlags(ThisPlayer, mx + w, my + h, 
+						mask & ((NumSelected && !CursorBuilding->BuilderOutside &&
 						Selected[0]->X == mx + w && Selected[0]->Y == my + h) ?
-							~(MapFieldLandUnit | MapFieldSeaUnit) : -1) &
-						(IsTileVisible(ThisPlayer, mx + w, my + h) == 1 ? 
-						~(MapFieldLandUnit | MapFieldSeaUnit | MapFieldBuilding) : -1)))
+							~(MapFieldLandUnit | MapFieldSeaUnit) : -1))))
 				  && IsMapFieldExplored(ThisPlayer, mx + w, my + h))  {
 				color = ColorGreen;
 			} else {