From 96eb6ca719cd53ed1cdee1fc819979492d02e078 Mon Sep 17 00:00:00 2001
From: George Mount <mount@google.com>
Date: Mon, 28 Nov 2016 15:08:19 -0800
Subject: [PATCH] Use transparent instead of null background during Activity
 Transitions

Bug 32952142

When doing activity transitions, a window is temporarily translucent
during the transition. When a view hierarchy completely covers the
window, the background is never seen and applications can use a
null background to avoid overdraw. However, during the activity
transition, the underlying activity is seen during the transition.
With a null background, the buffer isn't properly cleared and
the uncleared buffer will show strange effects.

This CL forces a transparent background temporarily during the
activity transition to avoid this problem.

Test: manual testing using test application

Change-Id: I63f24dba3c2f810944bcbf07faf309f9f1c5889a
---
 .../android/app/EnterTransitionCoordinator.java   | 15 +++++++++++++--
 .../android/app/ExitTransitionCoordinator.java    |  2 +-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/core/java/android/app/EnterTransitionCoordinator.java b/core/java/android/app/EnterTransitionCoordinator.java
index 3464c4d8cbeb4..7e0486f87ab1e 100644
--- a/core/java/android/app/EnterTransitionCoordinator.java
+++ b/core/java/android/app/EnterTransitionCoordinator.java
@@ -19,6 +19,8 @@ import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.animation.ObjectAnimator;
 import android.app.SharedElementCallback.OnSharedElementsReadyListener;
+import android.graphics.Color;
+import android.graphics.drawable.ColorDrawable;
 import android.graphics.drawable.Drawable;
 import android.os.Bundle;
 import android.os.ResultReceiver;
@@ -61,6 +63,7 @@ class EnterTransitionCoordinator extends ActivityTransitionCoordinator {
     private Transition mEnterViewsTransition;
     private OneShotPreDrawListener mViewsReadyListener;
     private final boolean mIsCrossTask;
+    private Drawable mReplacedBackground;
 
     public EnterTransitionCoordinator(Activity activity, ResultReceiver resultReceiver,
             ArrayList<String> sharedElementNames, boolean isReturning, boolean isCrossTask) {
@@ -332,12 +335,15 @@ class EnterTransitionCoordinator extends ActivityTransitionCoordinator {
         if (!mIsReturning) {
             mWasOpaque = mActivity.convertToTranslucent(null, null);
             Drawable background = decorView.getBackground();
-            if (background != null) {
+            if (background == null) {
+                background = new ColorDrawable(Color.TRANSPARENT);
+                mReplacedBackground = background;
+            } else {
                 getWindow().setBackgroundDrawable(null);
                 background = background.mutate();
                 background.setAlpha(0);
-                getWindow().setBackgroundDrawable(background);
             }
+            getWindow().setBackgroundDrawable(background);
         } else {
             mActivity = null; // all done with it now.
         }
@@ -553,6 +559,11 @@ class EnterTransitionCoordinator extends ActivityTransitionCoordinator {
         final ViewGroup decorView = getDecor();
         if (decorView != null) {
             decorView.sendAccessibilityEvent(AccessibilityEvent.TYPE_WINDOW_CONTENT_CHANGED);
+
+            Window window = getWindow();
+            if (window != null && mReplacedBackground == decorView.getBackground()) {
+                window.setBackgroundDrawable(null);
+            }
         }
     }
 
diff --git a/core/java/android/app/ExitTransitionCoordinator.java b/core/java/android/app/ExitTransitionCoordinator.java
index 6a79e6cfdf9cf..21e3aeedf69f1 100644
--- a/core/java/android/app/ExitTransitionCoordinator.java
+++ b/core/java/android/app/ExitTransitionCoordinator.java
@@ -236,7 +236,7 @@ class ExitTransitionCoordinator extends ActivityTransitionCoordinator {
             delayCancel();
             moveSharedElementsToOverlay();
             if (decorView != null && decorView.getBackground() == null) {
-                getWindow().setBackgroundDrawable(new ColorDrawable(Color.BLACK));
+                getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
             }
             final boolean targetsM = decorView == null || decorView.getContext()
                     .getApplicationInfo().targetSdkVersion >= VERSION_CODES.M;