From ff10d2bf526117fe1c83c76e1bc9e876d128666f Mon Sep 17 00:00:00 2001
From: Johannes Gallmann <gallmann@google.com>
Date: Wed, 7 Feb 2024 16:12:18 +0100
Subject: Fix small alpha flicker for cross activity back

Bug: 321964396
Flag: ACONFIG com.android.window.flags.predictive_back_system_anims TEAMFOOD
Test: Manual, i.e. veryfing that flicker does not occur anymore during cross activity back animation
Change-Id: Ifcd8ee11c661c1f7ff0ab1730569b34c78adece0
---
 .../wm/shell/back/CrossActivityBackAnimation.java   | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/back/CrossActivityBackAnimation.java b/libs/WindowManager/Shell/src/com/android/wm/shell/back/CrossActivityBackAnimation.java
index 160f922dd928..55982dca79b3 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/back/CrossActivityBackAnimation.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/back/CrossActivityBackAnimation.java
@@ -310,12 +310,16 @@ public class CrossActivityBackAnimation extends ShellBackAnimation {
         float top = mapRange(progress, mEnteringStartRect.top, mStartTaskRect.top);
         float width = mapRange(progress, mEnteringStartRect.width(), mStartTaskRect.width());
         float height = mapRange(progress, mEnteringStartRect.height(), mStartTaskRect.height());
-        float alpha = mapRange(progress, mEnteringProgress, 1.0f);
-
+        float alpha = mapRange(progress, getPreCommitEnteringAlpha(), 1.0f);
         mEnteringRect.set(left, top, left + width, top + height);
         applyTransform(mEnteringTarget.leash, mEnteringRect, alpha);
     }
 
+    private float getPreCommitEnteringAlpha() {
+        return Math.max(smoothstep(ENTER_ALPHA_THRESHOLD, 0.7f, mEnteringProgress),
+                MIN_WINDOW_ALPHA);
+    }
+
     private float getEnteringProgress() {
         return mEnteringProgress * SCALE_FACTOR;
     }
@@ -325,9 +329,7 @@ public class CrossActivityBackAnimation extends ShellBackAnimation {
         if (mEnteringTarget != null && mEnteringTarget.leash != null) {
             transformWithProgress(
                     mEnteringProgress,
-                    Math.max(
-                            smoothstep(ENTER_ALPHA_THRESHOLD, 0.7f, mEnteringProgress),
-                            MIN_WINDOW_ALPHA),  /* alpha */
+                    getPreCommitEnteringAlpha(),
                     mEnteringTarget.leash,
                     mEnteringRect,
                     -mWindowXShift,
@@ -336,6 +338,11 @@ public class CrossActivityBackAnimation extends ShellBackAnimation {
         }
     }
 
+    private float getPreCommitLeavingAlpha() {
+        return Math.max(1 - smoothstep(0, ENTER_ALPHA_THRESHOLD, mLeavingProgress),
+                MIN_WINDOW_ALPHA);
+    }
+
     private float getLeavingProgress() {
         return mLeavingProgress * SCALE_FACTOR;
     }
@@ -345,9 +352,7 @@ public class CrossActivityBackAnimation extends ShellBackAnimation {
         if (mClosingTarget != null && mClosingTarget.leash != null) {
             transformWithProgress(
                     mLeavingProgress,
-                    Math.max(
-                            1 - smoothstep(0, ENTER_ALPHA_THRESHOLD, mLeavingProgress),
-                            MIN_WINDOW_ALPHA),
+                    getPreCommitLeavingAlpha(),
                     mClosingTarget.leash,
                     mClosingRect,
                     0,
-- 
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