Preserve letterbox while dragResizing

Fixes an issue where the letterbox would disappear while entering
and leaving dragResizing, because this clears the hasDrawnState.

To fix this, also treat preserved surfaces as ready to show for
letterboxing purposes.

Change-Id: I4d6e1b1a27d99542370fde8924f126eca1ea80d5
Fixes: 76008154
Test: Enable double cutout, enter split screen, go home, touch slider verify the letterbox does not flicker.

1 files changed, 5 insertions, 3 deletions

diff --git a/services/core/java/com/android/server/wm/AppWindowToken.java b/services/core/java/com/android/server/wm/AppWindowToken.java
index d2ddf551fc8d..f77439e15caf 100644
--- a/services/core/java/com/android/server/wm/AppWindowToken.java
+++ b/services/core/java/com/android/server/wm/AppWindowToken.java
@@ -1471,11 +1471,13 @@ class AppWindowToken extends WindowToken implements WindowManagerService.AppFree
 
     void layoutLetterbox(WindowState winHint) {
         final WindowState w = findMainWindow();
-        if (w != winHint && winHint != null && w != null) {
+        if (w == null || winHint != null && w != winHint) {
             return;
         }
-        final boolean needsLetterbox = w != null && w.isLetterboxedAppWindow()
-                && fillsParent() && w.hasDrawnLw();
+        final boolean surfaceReady = w.hasDrawnLw()  // Regular case
+                || w.mWinAnimator.mSurfaceDestroyDeferred  // The preserved surface is still ready.
+                || w.isDragResizeChanged();  // Waiting for relayoutWindow to call preserveSurface.
+        final boolean needsLetterbox = w.isLetterboxedAppWindow() && fillsParent() && surfaceReady;
         if (needsLetterbox) {
             if (mLetterbox == null) {
                 mLetterbox = new Letterbox(() -> makeChildSurface(null));