Improve performance of window redraws

client/windows/CWindowObject.cpp

@@ -85,6 +85,7 @@ std::shared_ptr<CPicture> CWindowObject::createBg(std::string imageName, bool pl
 		return nullptr;
 
 	auto image = std::make_shared<CPicture>(imageName);
+	image->getSurface()->setBlitMode(EImageBlitMode::OPAQUE);
 	if(playerColored)
 		image->colorize(LOCPLINT->playerID);
 	return image;