(svn r26338) -Fix [FS#5908]: Don't redraw the link graph overlay if it's empty (MJP)

src/main_gui.cpp

@@ -253,11 +253,17 @@ struct MainWindow : Window
 
 	virtual void OnTick()
 	{
-		if (--refresh == 0) {
-			this->viewport->overlay->RebuildCache();
-			this->GetWidget<NWidgetBase>(WID_M_VIEWPORT)->SetDirty(this);
-			this->refresh = LINKGRAPH_REFRESH_PERIOD;
+		if (--this->refresh > 0) return;
+
+		this->refresh = LINKGRAPH_REFRESH_PERIOD;
+
+		if (this->viewport->overlay->GetCargoMask() == 0 ||
+				this->viewport->overlay->GetCompanyMask() == 0) {
+			return;
 		}
+
+		this->viewport->overlay->RebuildCache();
+		this->GetWidget<NWidgetBase>(WID_M_VIEWPORT)->SetDirty(this);
 	}
 
 	virtual void OnPaint()

src/viewport.cpp

@@ -1477,17 +1477,19 @@ void ViewportDoDraw(const ViewPort *vp, int left, int top, int right, int bottom
 	dp.height = UnScaleByZoom(dp.height, zoom);
 	_cur_dpi = &dp;
 
-	/* translate to window coordinates */
-	dp.left = x;
-	dp.top = y;
-
-	if (vp->overlay != NULL) vp->overlay->Draw(&dp);
-
-	/* translate back to world coordinates */
-	dp.left = UnScaleByZoom(_vd.dpi.left, zoom);
-	dp.top = UnScaleByZoom(_vd.dpi.top, zoom);
+	if (vp->overlay != NULL && vp->overlay->GetCargoMask() != 0 && vp->overlay->GetCompanyMask() != 0) {
+		/* translate to window coordinates */
+		dp.left = x;
+		dp.top = y;
+		vp->overlay->Draw(&dp);
+	}
 
-	if (_vd.string_sprites_to_draw.Length() != 0) ViewportDrawStrings(zoom, &_vd.string_sprites_to_draw);
+	if (_vd.string_sprites_to_draw.Length() != 0) {
+		/* translate to world coordinates */
+		dp.left = UnScaleByZoom(_vd.dpi.left, zoom);
+		dp.top = UnScaleByZoom(_vd.dpi.top, zoom);
+		ViewportDrawStrings(zoom, &_vd.string_sprites_to_draw);
+	}
 
 	_cur_dpi = old_dpi;