Fix flickering issues with divider during split animation

This CL makes changes to the "split divider placeholder view", which was intended to cover up the backdrop a little during the split confirm animation. The placeholder view is now larger (fullscreen) and fades in with the animation movement, so there is no longer a period of time when it looks like an awkward rectangle.

New timings and interpolators confirmed with UX. Also renamed some variables and added comments for clarity.

Fixes: 344573331
Test: Manually verified that the visual bug no longer happens on large and small screen, and from desktop and Overview.
Flag: EXEMPT bugfix
Change-Id: I3b37f2b0478035d7a3181ae7c23962fe75a13b2c

quickstep/src/com/android/quickstep/util/PhoneSplitToConfirmTimings.java

@@ -27,6 +27,8 @@ public class PhoneSplitToConfirmTimings
     public int getPlaceholderIconFadeInEnd() { return 133; }
     public int getStagedRectSlideStart() { return 0; }
     public int getStagedRectSlideEnd() { return 333; }
+    public int getBackingScrimFadeInStart() { return 0; }
+    public int getBackingScrimFadeInEnd() { return 266; }
 
     public int getDuration() { return PHONE_CONFIRM_DURATION; }
 }

quickstep/src/com/android/quickstep/util/SplitAnimationController.kt

@@ -281,64 +281,45 @@ class SplitAnimationController(val splitSelectStateController: SplitSelectStateC
     }
 
     /**
-     * Creates and returns a view to fade in at .4 animation progress and adds it to the provided
-     * [pendingAnimation]. Assumes that animation will be the final split placeholder launch anim.
-     *
-     * [secondPlaceholderEndingBounds] refers to the second placeholder view that gets added on
-     * screen, not the logical second app. For landscape it's the left app and for portrait the top
-     * one.
+     * Creates and returns a fullscreen scrim to fade in behind the split confirm animation, and
+     * adds it to the provided [pendingAnimation].
      */
-    fun addDividerPlaceholderViewToAnim(
+    fun addScrimBehindAnim(
         pendingAnimation: PendingAnimation,
         container: RecentsViewContainer,
-        secondPlaceholderEndingBounds: Rect,
         context: Context
     ): View {
-        val mSplitDividerPlaceholderView = View(context)
+        val scrim = View(context)
         val recentsView = container.getOverviewPanel<RecentsView<*, *>>()
-        val dp: com.android.launcher3.DeviceProfile = container.getDeviceProfile()
+        val dp: DeviceProfile = container.getDeviceProfile()
         // Add it before/under the most recently added first floating taskView
         val firstAddedSplitViewIndex: Int =
             container
                 .getDragLayer()
                 .indexOfChild(recentsView.splitSelectController.firstFloatingTaskView)
-        container.getDragLayer().addView(mSplitDividerPlaceholderView, firstAddedSplitViewIndex)
-        val lp = mSplitDividerPlaceholderView.layoutParams as InsettableFrameLayout.LayoutParams
+        container.getDragLayer().addView(scrim, firstAddedSplitViewIndex)
+        // Make the scrim fullscreen
+        val lp = scrim.layoutParams as InsettableFrameLayout.LayoutParams
         lp.topMargin = 0
+        lp.height = dp.heightPx
+        lp.width = dp.widthPx
 
-        if (dp.isLeftRightSplit) {
-            lp.height = secondPlaceholderEndingBounds.height()
-            lp.width =
-                container
-                    .asContext()
-                    .resources
-                    .getDimensionPixelSize(R.dimen.split_divider_handle_region_height)
-            mSplitDividerPlaceholderView.translationX =
-                secondPlaceholderEndingBounds.right - lp.width / 2f
-            mSplitDividerPlaceholderView.translationY = 0f
-        } else {
-            lp.height =
-                container
-                    .asContext()
-                    .resources
-                    .getDimensionPixelSize(R.dimen.split_divider_handle_region_height)
-            lp.width = secondPlaceholderEndingBounds.width()
-            mSplitDividerPlaceholderView.translationY =
-                secondPlaceholderEndingBounds.top - lp.height / 2f
-            mSplitDividerPlaceholderView.translationX = 0f
-        }
-
-        mSplitDividerPlaceholderView.alpha = 0f
-        mSplitDividerPlaceholderView.setBackgroundColor(
+        scrim.alpha = 0f
+        scrim.setBackgroundColor(
             container.asContext().resources.getColor(R.color.taskbar_background_dark)
         )
-        val timings = AnimUtils.getDeviceSplitToConfirmTimings(dp.isTablet)
+        val timings = AnimUtils.getDeviceSplitToConfirmTimings(dp.isTablet) as SplitToConfirmTimings
         pendingAnimation.setViewAlpha(
-            mSplitDividerPlaceholderView,
+            scrim,
             1f,
-            Interpolators.clampToProgress(timings.stagedRectScaleXInterpolator, 0.4f, 1f)
+            Interpolators.clampToProgress(
+                timings.backingScrimFadeInterpolator,
+                timings.backingScrimFadeInStartOffset,
+                timings.backingScrimFadeInEndOffset
+            )
         )
-        return mSplitDividerPlaceholderView
+
+        return scrim
     }
 
     /** Does not play any animation if user is not currently in split selection state. */

quickstep/src/com/android/quickstep/util/SplitToConfirmTimings.java

@@ -17,6 +17,7 @@
 package com.android.quickstep.util;
 
 import static com.android.app.animation.Interpolators.EMPHASIZED;
+import static com.android.app.animation.Interpolators.LINEAR;
 
 import android.view.animation.Interpolator;
 
@@ -31,6 +32,8 @@ abstract class SplitToConfirmTimings implements SplitAnimationTimings {
     abstract public int getPlaceholderIconFadeInEnd();
     abstract public int getStagedRectSlideStart();
     abstract public int getStagedRectSlideEnd();
+    abstract public int getBackingScrimFadeInStart();
+    abstract public int getBackingScrimFadeInEnd();
 
     // Common timings
     public int getInstructionsFadeStart() { return 0; }
@@ -39,6 +42,7 @@ abstract class SplitToConfirmTimings implements SplitAnimationTimings {
     public Interpolator getStagedRectYInterpolator() { return EMPHASIZED; }
     public Interpolator getStagedRectScaleXInterpolator() { return EMPHASIZED; }
     public Interpolator getStagedRectScaleYInterpolator() { return EMPHASIZED; }
+    public Interpolator getBackingScrimFadeInterpolator() { return LINEAR; }
 
     abstract public int getDuration();
 
@@ -48,4 +52,10 @@ abstract class SplitToConfirmTimings implements SplitAnimationTimings {
     public float getInstructionsFadeEndOffset() {
         return (float) getInstructionsFadeEnd() / getDuration();
     }
+    public float getBackingScrimFadeInStartOffset() {
+        return (float) getBackingScrimFadeInStart() / getDuration();
+    }
+    public float getBackingScrimFadeInEndOffset() {
+        return (float) getBackingScrimFadeInEnd() / getDuration();
+    }
 }

quickstep/src/com/android/quickstep/util/SplitToWorkspaceController.java

@@ -163,9 +163,8 @@ public class SplitToWorkspaceController {
                 new RectF(firstTaskStartingBounds), firstTaskEndingBounds,
                 false /* fadeWithThumbnail */, true /* isStagedTask */);
 
-        View mSplitDividerPlaceholderView = recentsView.getSplitSelectController()
-                .getSplitAnimationController().addDividerPlaceholderViewToAnim(pendingAnimation,
-                        mLauncher, secondTaskEndingBounds, view.getContext());
+        View backingScrim = recentsView.getSplitSelectController().getSplitAnimationController()
+                .addScrimBehindAnim(pendingAnimation, mLauncher, view.getContext());
 
         FloatingTaskView secondFloatingTaskView = FloatingTaskView.getFloatingTaskView(mLauncher,
                 view, bitmap, icon, secondTaskStartingBounds);
@@ -197,7 +196,7 @@ public class SplitToWorkspaceController {
             private void cleanUp() {
                 mLauncher.getDragLayer().removeView(firstFloatingTaskView);
                 mLauncher.getDragLayer().removeView(secondFloatingTaskView);
-                mLauncher.getDragLayer().removeView(mSplitDividerPlaceholderView);
+                mLauncher.getDragLayer().removeView(backingScrim);
                 mController.getSplitAnimationController().removeSplitInstructionsView(mLauncher);
                 mController.resetState();
             }

quickstep/src/com/android/quickstep/util/TabletSplitToConfirmTimings.java

@@ -27,6 +27,8 @@ public class TabletSplitToConfirmTimings
     public int getPlaceholderIconFadeInEnd() { return 250; }
     public int getStagedRectSlideStart() { return 0; }
     public int getStagedRectSlideEnd() { return 500; }
+    public int getBackingScrimFadeInStart() { return 0; }
+    public int getBackingScrimFadeInEnd() { return 400; }
 
     public int getDuration() { return TABLET_CONFIRM_DURATION; }
 }

quickstep/src/com/android/quickstep/views/RecentsView.java

@@ -738,7 +738,11 @@ public abstract class RecentsView<CONTAINER_TYPE extends Context & RecentsViewCo
     private int mSplitHiddenTaskViewIndex = -1;
     @Nullable
     private FloatingTaskView mSecondFloatingTaskView;
-    private View mSplitDividerPlaceholderView;
+    /**
+     * A fullscreen scrim that goes behind the splitscreen animation to hide color conflicts and
+     * possible flickers. Removed after tasks + divider finish animating in.
+     */
+    private View mSplitScrim;
 
     /**
      * The task to be removed and immediately re-added. Should not be added to task pool.
@@ -4926,9 +4930,8 @@ public abstract class RecentsView<CONTAINER_TYPE extends Context & RecentsViewCo
                 mSplitSelectStateController.getActiveSplitStagePosition(), firstTaskEndingBounds,
                 secondTaskEndingBounds);
 
-        mSplitDividerPlaceholderView = mSplitSelectStateController
-                .getSplitAnimationController().addDividerPlaceholderViewToAnim(pendingAnimation,
-                        mContainer, secondTaskEndingBounds, getContext());
+        mSplitScrim = mSplitSelectStateController.getSplitAnimationController()
+                .addScrimBehindAnim(pendingAnimation, mContainer, getContext());
         FloatingTaskView firstFloatingTaskView =
                 mSplitSelectStateController.getFirstFloatingTaskView();
         firstFloatingTaskView.getBoundsOnScreen(firstTaskStartingBounds);
@@ -4983,7 +4986,7 @@ public abstract class RecentsView<CONTAINER_TYPE extends Context & RecentsViewCo
             safeRemoveDragLayerView(mSplitSelectStateController.getFirstFloatingTaskView());
             safeRemoveDragLayerView(mSecondFloatingTaskView);
             safeRemoveDragLayerView(mSplitSelectStateController.getSplitInstructionsView());
-            safeRemoveDragLayerView(mSplitDividerPlaceholderView);
+            safeRemoveDragLayerView(mSplitScrim);
             mSecondFloatingTaskView = null;
             mSplitSelectSource = null;
             mSplitSelectStateController.getSplitAnimationController()