Merge "Do not redraw if no change on reparent" into udc-dev

services/core/java/com/android/server/wm/WindowContainer.java

@@ -3993,6 +3993,9 @@ class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<
             }
             // Otherwise this is the "root" of a synced subtree, so continue on to preparation.
         }
+        if (oldParent != null && newParent != null && !shouldUpdateSyncOnReparent()) {
+            return;
+        }
 
         // This container's situation has changed so we need to restart its sync.
         // We cannot reset the sync without a chance of a deadlock since it will request a new
@@ -4007,6 +4010,11 @@ class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<
         prepareSync();
     }
 
+    /** Returns {@code true} if {@link #mSyncState} needs to be updated when reparenting. */
+    protected boolean shouldUpdateSyncOnReparent() {
+        return true;
+    }
+
     void registerWindowContainerListener(WindowContainerListener listener) {
         registerWindowContainerListener(listener, true /* shouldPropConfig */);
     }

services/core/java/com/android/server/wm/WindowState.java

@@ -5634,6 +5634,13 @@ class WindowState extends WindowContainer<WindowState> implements WindowManagerP
         t.unsetBuffer(viewSurface);
     }
 
+    @Override
+    protected boolean shouldUpdateSyncOnReparent() {
+        // Keep the sync state in case the client is drawing for the latest conifguration or the
+        // configuration is not changed after reparenting. This avoids a redundant redraw request.
+        return mSyncState != SYNC_STATE_NONE && !mLastConfigReportedToClient;
+    }
+
     @Override
     boolean prepareSync() {
         if (!mDrawHandlers.isEmpty()) {

services/tests/wmtests/src/com/android/server/wm/SyncEngineTests.java

@@ -26,6 +26,7 @@ import static com.android.server.wm.BLASTSyncEngine.METHOD_NONE;
 import static com.android.server.wm.WindowContainer.POSITION_BOTTOM;
 import static com.android.server.wm.WindowContainer.POSITION_TOP;
 import static com.android.server.wm.WindowContainer.SYNC_STATE_NONE;
+import static com.android.server.wm.WindowContainer.SYNC_STATE_READY;
 import static com.android.server.wm.WindowState.BLAST_TIMEOUT_DURATION;
 
 import static org.junit.Assert.assertEquals;
@@ -38,7 +39,9 @@ import static org.mockito.ArgumentMatchers.notNull;
 import static org.mockito.Mockito.spy;
 
 import android.platform.test.annotations.Presubmit;
+import android.util.MergedConfiguration;
 import android.view.SurfaceControl;
+import android.window.ClientWindowFrames;
 
 import androidx.test.filters.SmallTest;
 
@@ -306,6 +309,19 @@ public class SyncEngineTests extends WindowTestsBase {
         assertEquals(SYNC_STATE_NONE, parentWC.mSyncState);
         assertEquals(SYNC_STATE_NONE, topChildWC.mSyncState);
         assertEquals(SYNC_STATE_NONE, botChildWC.mSyncState);
+
+        // If the appearance of window won't change after reparenting, its sync state can be kept.
+        final WindowState w = createWindow(null, TYPE_BASE_APPLICATION, "win");
+        parentWC.onRequestedOverrideConfigurationChanged(w.getConfiguration());
+        w.reparent(botChildWC, POSITION_TOP);
+        parentWC.prepareSync();
+        // Assume the window has drawn with the latest configuration.
+        w.fillClientWindowFramesAndConfiguration(new ClientWindowFrames(),
+                new MergedConfiguration(), true /* useLatestConfig */, true /* relayoutVisible */);
+        assertTrue(w.onSyncFinishedDrawing());
+        assertEquals(SYNC_STATE_READY, w.mSyncState);
+        w.reparent(topChildWC, POSITION_TOP);
+        assertEquals(SYNC_STATE_READY, w.mSyncState);
     }
 
     @Test