From 2da185d516d4441f0ea6aab4e42ea77845607fc9 Mon Sep 17 00:00:00 2001
From: Evan Rosky <erosky@google.com>
Date: Thu, 19 Nov 2020 20:20:53 -0800
Subject: [PATCH] Don't updateSurfacePosition with invalid window frames

updateSurfacePosition runs pretty frequently (during
configuration update). However, the WindowState override
relies on mWindowFrames which is calculated during layout.
This means that surface positions are frequently calculated
with out-of-date mWindowFrames (most commonly when the
onConfigurationChange cascade is called). This can easily
cause visible glitching based on the timings of SFTransaction
applications -- particularly when mixed with syncTransactions
since those aren't serialized with layout.

This CL prevents WindowState's updateSurfacePosition from
running when layout is deferred or when the window is
goneForLayout.

Bug: 169035082
Test: With new split-screen transitions, launch a non-resizable
      task while in split-screen and observe that home surface
      doesn't get repositioned incorrectly.
Change-Id: If35fb3560eed83fe1c944a1cb7cbb685f58a3b90
---
 services/core/java/com/android/server/wm/WindowState.java   | 6 ++++++
 .../wmtests/src/com/android/server/wm/WindowStateTests.java | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/services/core/java/com/android/server/wm/WindowState.java b/services/core/java/com/android/server/wm/WindowState.java
index b5509f62f92a8..008a7a68ab334 100644
--- a/services/core/java/com/android/server/wm/WindowState.java
+++ b/services/core/java/com/android/server/wm/WindowState.java
@@ -5262,6 +5262,12 @@ class WindowState extends WindowContainer<WindowState> implements WindowManagerP
         if (mSurfaceControl == null) {
             return;
         }
+        if (mWmService.mWindowPlacerLocked.isLayoutDeferred() || isGoneForLayout()) {
+            // Since this relies on mWindowFrames, changes made while layout is deferred are
+            // likely to be invalid. Similarly, if it's goneForLayout, mWindowFrames may not be
+            // up-to-date and thus can't be relied on.
+            return;
+        }
 
         transformFrameToSurfacePosition(mWindowFrames.mFrame.left, mWindowFrames.mFrame.top,
                 mSurfacePosition);
diff --git a/services/tests/wmtests/src/com/android/server/wm/WindowStateTests.java b/services/tests/wmtests/src/com/android/server/wm/WindowStateTests.java
index 75d2c5159187a..12746b1bd4c3f 100644
--- a/services/tests/wmtests/src/com/android/server/wm/WindowStateTests.java
+++ b/services/tests/wmtests/src/com/android/server/wm/WindowStateTests.java
@@ -647,6 +647,8 @@ public class WindowStateTests extends WindowTestsBase {
         win1.mSurfaceControl = mock(SurfaceControl.class);
         win1.mAttrs.surfaceInsets.set(1, 2, 3, 4);
         win1.getFrame().offsetTo(WINDOW_OFFSET, 0);
+        // Simulate layout
+        win1.mRelayoutCalled = true;
         win1.updateSurfacePosition(t);
         win1.getTransformationMatrix(values, matrix);