platforms/drm: Enable buffer age for all outputs

plugins/platforms/drm/egl_gbm_backend.cpp

@@ -568,7 +568,7 @@ void EglGbmBackend::endRenderingFrameForScreen(int screenId,
     Output &output = m_outputs[screenId];
     renderFramebufferToSurface(output);
 
-    if (damagedRegion.intersected(output.output->geometry()).isEmpty() && screenId == 0) {
+    if (damagedRegion.intersected(output.output->geometry()).isEmpty()) {
 
         // If the damaged region of a window is fully occluded, the only
         // rendering done, if any, will have been to repair a reused back
@@ -580,22 +580,12 @@ void EglGbmBackend::endRenderingFrameForScreen(int screenId,
         if (!renderedRegion.intersected(output.output->geometry()).isEmpty())
             glFlush();
 
-        for (auto &output: m_outputs) {
-            output.bufferAge = 1;
-        }
+        output.bufferAge = 1;
         return;
     }
     presentOnOutput(output, damagedRegion);
 
-    // Save the damaged region to history
-    // Note: damage history is only collected for the first screen. For any other screen full
-    // repaints are triggered. This is due to a limitation in Scene::paintGenericScreen which resets
-    // the Toplevel's repaint. So multiple calls to Scene::paintScreen as it's done in multi-output
-    // rendering only have correct damage information for the first screen. If we try to track
-    // damage nevertheless, it creates artifacts. So for the time being we work around the problem
-    // by only supporting buffer age on the first output. To properly support buffer age on all
-    // outputs the rendering needs to be refactored in general.
-    if (supportsBufferAge() && screenId == 0) {
+    if (supportsBufferAge()) {
         if (output.damageHistory.count() > 10) {
             output.damageHistory.removeLast();
         }