(svn r20962) -Fix [FS#4166](r20956): Determine tile under cursor before opening the new viewport. It might appear just below the cursor.

src/gui.h

@@ -66,6 +66,7 @@ enum WarningLevel {
 void ShowErrorMessage(StringID summary_msg, StringID detailed_msg, WarningLevel wl, int x = 0, int y = 0);
 
 void ShowExtraViewPortWindow(TileIndex tile = INVALID_TILE);
+void ShowExtraViewPortWindowForTileUnderCursor();
 
 /* bridge_gui.cpp */
 void ShowBuildBridgeWindow(TileIndex start, TileIndex end, TransportType transport_type, byte bridge_type);

src/toolbar_gui.cpp

@@ -1343,7 +1343,7 @@ struct MainToolbarWindow : Window {
 			case MTHK_GIANT_SCREENSHOT: MenuClickWorldScreenshot(); break;
 			case MTHK_CHEATS: if (!_networking) ShowCheatWindow(); break;
 			case MTHK_TERRAFORM: ShowTerraformToolbar(); break;
-			case MTHK_EXTRA_VIEWPORT: ShowExtraViewPortWindow(); break;
+			case MTHK_EXTRA_VIEWPORT: ShowExtraViewPortWindowForTileUnderCursor(); break;
 #ifdef ENABLE_NETWORK
 			case MTHK_CLIENT_LIST: if (_networking) ShowClientList(); break;
 #endif
@@ -1645,7 +1645,7 @@ public:
 			case MTEHK_ZOOM_OUT: ToolbarZoomOutClick(this); break;
 			case MTEHK_TERRAFORM: ShowEditorTerraformToolbar(); break;
 			case MTEHK_SMALLMAP: ShowSmallMap(); break;
-			case MTEHK_EXTRA_VIEWPORT: ShowExtraViewPortWindow(); break;
+			case MTEHK_EXTRA_VIEWPORT: ShowExtraViewPortWindowForTileUnderCursor(); break;
 			default: return ES_NOT_HANDLED;
 		}
 		return ES_HANDLED;

src/viewport_gui.cpp

@@ -71,12 +71,7 @@ public:
 
 		Point pt;
 		if (tile == INVALID_TILE) {
-			/* Use tile under mouse as center for new viewport */
-			Point pt = GetTileBelowCursor();
-			if (pt.x != -1) tile = TileVirtXY(pt.x, pt.y);
-		}
-		if (tile == INVALID_TILE) {
-			/* Still no tile? Use center of main viewport. */
+			/* No tile? Use center of main viewport. */
 			const Window *w = FindWindowById(WC_MAIN_WINDOW, 0);
 
 			/* center on same place as main window (zoom is maximum, no adjustment needed) */
@@ -175,6 +170,10 @@ static const WindowDesc _extra_view_port_desc(
 	_nested_extra_view_port_widgets, lengthof(_nested_extra_view_port_widgets)
 );
 
+/**
+ * Show a new Extra Viewport window.
+ * @param tile Tile to center the view on. INVALID_TILE means to use the center of main viewport.
+ */
 void ShowExtraViewPortWindow(TileIndex tile)
 {
 	int i = 0;
@@ -184,3 +183,16 @@ void ShowExtraViewPortWindow(TileIndex tile)
 
 	new ExtraViewportWindow(&_extra_view_port_desc, i, tile);
 }
+
+/**
+ * Show a new Extra Viewport window.
+ * Center it on the tile under the cursor, if the cursor is inside a viewport.
+ * If that fails, center it on main viewport center.
+ */
+void ShowExtraViewPortWindowForTileUnderCursor()
+{
+	/* Use tile under mouse as center for new viewport.
+	 * Do this before creating the window, it might appear just below the mouse. */
+	Point pt = GetTileBelowCursor();
+	ShowExtraViewPortWindow(pt.x != -1 ? TileVirtXY(pt.x, pt.y) : INVALID_TILE);
+}