Fix dragging window from non-retina to retina display.

platform/osx/os_osx.mm

@@ -263,6 +263,7 @@ static Vector2 get_mouse_pos(NSEvent *event) {
 	NSWindow *window = (NSWindow *)[notification object];
 	CGFloat newBackingScaleFactor = [window backingScaleFactor];
 	CGFloat oldBackingScaleFactor = [[[notification userInfo] objectForKey:@"NSBackingPropertyOldScaleFactorKey"] doubleValue];
+	[OS_OSX::singleton->window_view setWantsBestResolutionOpenGLSurface:YES];
 
 	if (newBackingScaleFactor != oldBackingScaleFactor) {
 		//Set new display scale and window size