cleaner approach to handling the viewport bug

src/glstate.h

@@ -52,6 +52,10 @@ struct GLProperty
 		set(value);
 	}
 
+	void refresh()
+	{
+		apply(current);
+	}
 private:
 	virtual void apply(const T &value) = 0;
 

src/graphics.cpp

@@ -469,7 +469,8 @@ struct GraphicsPrivate
 	{
 		if (threadData->windowSizeMsg.pollChange(&winSize.x, &winSize.y))
 		{
-			glState.viewport.init(IntRect(0, 0, winSize.x, winSize.y));
+			// some GL drivers change the viewport on window resize
+			glState.viewport.refresh();
 			recalculateScreenSize();
 			screen.setScreenSize(winSize.x, winSize.y);
 			updateScreenResoRatio();