scene: Set render target rect in Scene::paintScreen()

This ensures that the render target rect is set when using qpainter
render backend.

src/scene.cpp

@@ -257,11 +257,8 @@ void Scene::paintScreen(AbstractOutput *output, const QList<Toplevel *> &topleve
     createStackingOrder(toplevels);
     painted_screen = output;
 
-    setRenderTargetRect(output->geometry());
-    setRenderTargetScale(output->scale());
-
     QRegion update, valid;
-    paintScreen(renderTargetRect(), QRect(), &update, &valid);
+    paintScreen(output->geometry(), QRect(), &update, &valid);
     clearStackingOrder();
 }
 
@@ -286,6 +283,14 @@ void Scene::paintScreen(const QRegion &damage, const QRegion &repaint,
     auto effectsImpl = static_cast<EffectsHandlerImpl *>(effects);
     effectsImpl->startPaint();
 
+    if (kwinApp()->platform()->isPerScreenRenderingEnabled()) {
+        setRenderTargetRect(painted_screen->geometry());
+        setRenderTargetScale(painted_screen->scale());
+    } else {
+        setRenderTargetRect(geometry());
+        setRenderTargetScale(1);
+    }
+
     const QRegion displayRegion(renderTargetRect());
     QRegion region = damage;
 

src/scenes/opengl/scene_opengl.cpp

@@ -195,14 +195,6 @@ void SceneOpenGL::paint(AbstractOutput *output, const QRegion &damage, const QLi
     QRegion valid;
     QRegion repaint;
 
-    if (kwinApp()->platform()->isPerScreenRenderingEnabled()) {
-        setRenderTargetRect(output->geometry());
-        setRenderTargetScale(output->scale());
-    } else {
-        setRenderTargetRect(geometry());
-        setRenderTargetScale(1);
-    }
-
     renderLoop->beginFrame();
 
     SurfaceItem *fullscreenSurface = nullptr;