[PiP2] Implement expand PiP to Split CUJ

Whenever PiP enters from a multi-activity task,
the last parent before PiP can enter split-screen.
So we detect whether that's happened and expand into the split
instead of fullscreen, depending on the context.

This is also the first CL that is cleaning up PipTransition by
separating it into smaller handlers. Here we are adding a new
PipExpandHandler that PipTransition delegates the transition resolution
and animation to if needed.

Also added a new PipExpandHandlerTest in the effort to make PiP
transitions more covered by unit tests.

Bug: 381330052
Flag: com.android.wm.shell.enable_pip2
Test: enter multi-activity PiP from split, then expand from PiP
Test: atest WMShellUnitTests:PipSchedulerTest
Test: atest WMShellUnitTests:PipExpandHandlerTest
Change-Id: I660176dc1a247613aafdf1fa06db3dfec10ad597

9 files changed, 758 insertions, 177 deletions

diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/pip/Pip2Module.java b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/pip/Pip2Module.java
index 7d80ee5f3bb6..f8b18f29c797 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/pip/Pip2Module.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/dagger/pip/Pip2Module.java
@@ -53,6 +53,7 @@ import com.android.wm.shell.pip2.phone.PipTransition;
 import com.android.wm.shell.pip2.phone.PipTransitionState;
 import com.android.wm.shell.pip2.phone.PipUiStateChangeController;
 import com.android.wm.shell.shared.annotations.ShellMainThread;
+import com.android.wm.shell.splitscreen.SplitScreenController;
 import com.android.wm.shell.sysui.ShellCommandHandler;
 import com.android.wm.shell.sysui.ShellController;
 import com.android.wm.shell.sysui.ShellInit;
@@ -85,11 +86,13 @@ public abstract class Pip2Module {
             @NonNull PipDisplayLayoutState pipDisplayLayoutState,
             @NonNull PipUiStateChangeController pipUiStateChangeController,
             DisplayController displayController,
+            Optional<SplitScreenController> splitScreenControllerOptional,
             PipDesktopState pipDesktopState) {
         return new PipTransition(context, shellInit, shellTaskOrganizer, transitions,
                 pipBoundsState, null, pipBoundsAlgorithm, pipTaskListener,
                 pipScheduler, pipStackListenerController, pipDisplayLayoutState,
-                pipUiStateChangeController, displayController, pipDesktopState);
+                pipUiStateChangeController, displayController, splitScreenControllerOptional,
+                pipDesktopState);
     }
 
     @WMSingleton
@@ -140,9 +143,10 @@ public abstract class Pip2Module {
             PipBoundsState pipBoundsState,
             @ShellMainThread ShellExecutor mainExecutor,
             PipTransitionState pipTransitionState,
+            Optional<SplitScreenController> splitScreenControllerOptional,
             PipDesktopState pipDesktopState) {
         return new PipScheduler(context, pipBoundsState, mainExecutor, pipTransitionState,
-                pipDesktopState);
+                splitScreenControllerOptional, pipDesktopState);
     }
 
     @WMSingleton
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/pip/PipTransitionController.java b/libs/WindowManager/Shell/src/com/android/wm/shell/pip/PipTransitionController.java
index da3181096d98..cef18f55b86d 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/pip/PipTransitionController.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/pip/PipTransitionController.java
@@ -145,7 +145,7 @@ public abstract class PipTransitionController implements Transitions.TransitionH
     /**
      * Called when the Shell wants to start an exit-via-expand from Pip transition/animation.
      */
-    public void startExpandTransition(WindowContainerTransaction out) {
+    public void startExpandTransition(WindowContainerTransaction out, boolean toSplit) {
         // Default implementation does nothing.
     }
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipScheduler.java b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipScheduler.java
index e17587ff18bc..df7a25af8376 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipScheduler.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipScheduler.java
@@ -35,6 +35,10 @@ import com.android.wm.shell.pip.PipTransitionController;
 import com.android.wm.shell.pip2.PipSurfaceTransactionHelper;
 import com.android.wm.shell.pip2.animation.PipAlphaAnimator;
 import com.android.wm.shell.protolog.ShellProtoLogGroup;
+import com.android.wm.shell.shared.split.SplitScreenConstants;
+import com.android.wm.shell.splitscreen.SplitScreenController;
+
+import java.util.Optional;
 
 /**
  * Scheduler for Shell initiated PiP transitions and animations.
@@ -47,6 +51,7 @@ public class PipScheduler {
     private final ShellExecutor mMainExecutor;
     private final PipTransitionState mPipTransitionState;
     private final PipDesktopState mPipDesktopState;
+    private final Optional<SplitScreenController> mSplitScreenControllerOptional;
     private PipTransitionController mPipTransitionController;
     private PipSurfaceTransactionHelper.SurfaceControlTransactionFactory
             mSurfaceControlTransactionFactory;
@@ -59,12 +64,14 @@ public class PipScheduler {
             PipBoundsState pipBoundsState,
             ShellExecutor mainExecutor,
             PipTransitionState pipTransitionState,
+            Optional<SplitScreenController> splitScreenControllerOptional,
             PipDesktopState pipDesktopState) {
         mContext = context;
         mPipBoundsState = pipBoundsState;
         mMainExecutor = mainExecutor;
         mPipTransitionState = pipTransitionState;
         mPipDesktopState = pipDesktopState;
+        mSplitScreenControllerOptional = splitScreenControllerOptional;
 
         mSurfaceControlTransactionFactory =
                 new PipSurfaceTransactionHelper.VsyncSurfaceControlTransactionFactory();
@@ -96,10 +103,23 @@ public class PipScheduler {
     public void scheduleExitPipViaExpand() {
         mMainExecutor.execute(() -> {
             if (!mPipTransitionState.isInPip()) return;
-            WindowContainerTransaction wct = getExitPipViaExpandTransaction();
-            if (wct != null) {
-                mPipTransitionController.startExpandTransition(wct);
-            }
+
+            final WindowContainerTransaction expandWct = getExitPipViaExpandTransaction();
+            if (expandWct == null) return;
+
+            final WindowContainerTransaction wct = new WindowContainerTransaction();
+            mSplitScreenControllerOptional.ifPresent(splitScreenController -> {
+                int lastParentTaskId = mPipTransitionState.getPipTaskInfo()
+                        .lastParentTaskIdBeforePip;
+                if (splitScreenController.isTaskInSplitScreen(lastParentTaskId)) {
+                    splitScreenController.prepareEnterSplitScreen(wct,
+                            null /* taskInfo */, SplitScreenConstants.SPLIT_POSITION_UNDEFINED);
+                }
+            });
+
+            boolean toSplit = !wct.isEmpty();
+            wct.merge(expandWct, true /* transfer */);
+            mPipTransitionController.startExpandTransition(wct, toSplit);
         });
     }
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransition.java b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransition.java
index a57b4b948b42..a4eb5cd8e896 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransition.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransition.java
@@ -16,7 +16,6 @@
 
 package com.android.wm.shell.pip2.phone;
 
-import static android.app.WindowConfiguration.ROTATION_UNDEFINED;
 import static android.app.WindowConfiguration.WINDOWING_MODE_PINNED;
 import static android.app.WindowConfiguration.WINDOWING_MODE_UNDEFINED;
 import static android.view.Surface.ROTATION_0;
@@ -29,7 +28,13 @@ import static android.view.WindowManager.TRANSIT_PIP;
 import static android.view.WindowManager.TRANSIT_TO_BACK;
 import static android.view.WindowManager.TRANSIT_TO_FRONT;
 
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getChangeByToken;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getFixedRotationDelta;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getLeash;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getPipChange;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getPipParams;
 import static com.android.wm.shell.transition.Transitions.TRANSIT_EXIT_PIP;
+import static com.android.wm.shell.transition.Transitions.TRANSIT_EXIT_PIP_TO_SPLIT;
 import static com.android.wm.shell.transition.Transitions.TRANSIT_REMOVE_PIP;
 import static com.android.wm.shell.transition.Transitions.TRANSIT_RESIZE_PIP;
 import static com.android.wm.shell.transition.Transitions.transitTypeToString;
@@ -45,7 +50,6 @@ import android.graphics.PointF;
 import android.graphics.Rect;
 import android.os.Bundle;
 import android.os.IBinder;
-import android.view.Surface;
 import android.view.SurfaceControl;
 import android.view.WindowManager;
 import android.window.TransitionInfo;
@@ -70,11 +74,14 @@ import com.android.wm.shell.pip.PipTransitionController;
 import com.android.wm.shell.pip2.PipSurfaceTransactionHelper;
 import com.android.wm.shell.pip2.animation.PipAlphaAnimator;
 import com.android.wm.shell.pip2.animation.PipEnterAnimator;
-import com.android.wm.shell.pip2.animation.PipExpandAnimator;
+import com.android.wm.shell.pip2.phone.transition.PipExpandHandler;
 import com.android.wm.shell.shared.TransitionUtil;
+import com.android.wm.shell.splitscreen.SplitScreenController;
 import com.android.wm.shell.sysui.ShellInit;
 import com.android.wm.shell.transition.Transitions;
 
+import java.util.Optional;
+
 /**
  * Implementation of transitions for PiP on phone.
  */
@@ -130,6 +137,7 @@ public class PipTransition extends PipTransitionController implements
     //
     // Internal state and relevant cached info
     //
+    private final PipExpandHandler mExpandHandler;
 
     private Transitions.TransitionFinishCallback mFinishCallback;
 
@@ -151,6 +159,7 @@ public class PipTransition extends PipTransitionController implements
             PipDisplayLayoutState pipDisplayLayoutState,
             PipUiStateChangeController pipUiStateChangeController,
             DisplayController displayController,
+            Optional<SplitScreenController> splitScreenControllerOptional,
             PipDesktopState pipDesktopState) {
         super(shellInit, shellTaskOrganizer, transitions, pipBoundsState, pipMenuController,
                 pipBoundsAlgorithm);
@@ -165,6 +174,9 @@ public class PipTransition extends PipTransitionController implements
         mDisplayController = displayController;
         mPipSurfaceTransactionHelper = new PipSurfaceTransactionHelper(mContext);
         mPipDesktopState = pipDesktopState;
+
+        mExpandHandler = new PipExpandHandler(mContext, pipBoundsState, pipBoundsAlgorithm,
+                pipTransitionState, pipDisplayLayoutState, splitScreenControllerOptional);
     }
 
     @Override
@@ -184,10 +196,11 @@ public class PipTransition extends PipTransitionController implements
     //
 
     @Override
-    public void startExpandTransition(WindowContainerTransaction out) {
+    public void startExpandTransition(WindowContainerTransaction out, boolean toSplit) {
         if (out == null) return;
         mPipTransitionState.setState(PipTransitionState.EXITING_PIP);
-        mExitViaExpandTransition = mTransitions.startTransition(TRANSIT_EXIT_PIP, out, this);
+        mExitViaExpandTransition = mTransitions.startTransition(toSplit ? TRANSIT_EXIT_PIP_TO_SPLIT
+                : TRANSIT_EXIT_PIP, out, this);
     }
 
     @Override
@@ -239,10 +252,11 @@ public class PipTransition extends PipTransitionController implements
             @NonNull SurfaceControl.Transaction finishT,
             @NonNull IBinder mergeTarget,
             @NonNull Transitions.TransitionFinishCallback finishCallback) {
-        // Just jump-cut the current animation if any, but do not merge.
         if (info.getType() == TRANSIT_EXIT_PIP) {
             end();
         }
+        mExpandHandler.mergeAnimation(transition, info, startT, finishT, mergeTarget,
+                finishCallback);
     }
 
     @Override
@@ -290,7 +304,8 @@ public class PipTransition extends PipTransitionController implements
                     finishCallback);
         } else if (transition == mExitViaExpandTransition) {
             mExitViaExpandTransition = null;
-            return startExpandAnimation(info, startTransaction, finishTransaction, finishCallback);
+            return mExpandHandler.startAnimation(transition, info, startTransaction,
+                    finishTransaction, finishCallback);
         } else if (transition == mResizeTransition) {
             mResizeTransition = null;
             return startResizeAnimation(info, startTransaction, finishTransaction, finishCallback);
@@ -433,7 +448,7 @@ public class PipTransition extends PipTransitionController implements
                             (destinationBounds.height() - overlaySize) / 2f);
         }
 
-        final int delta = getFixedRotationDelta(info, pipChange);
+        final int delta = getFixedRotationDelta(info, pipChange, mPipDisplayLayoutState);
         if (delta != ROTATION_0) {
             // Update transition target changes in place to prepare for fixed rotation.
             handleBoundsEnterFixedRotation(info, pipChange, pipActivityChange);
@@ -493,7 +508,7 @@ public class PipTransition extends PipTransitionController implements
         final Rect adjustedSourceRectHint = getAdjustedSourceRectHint(info, pipChange,
                 pipActivityChange);
 
-        final int delta = getFixedRotationDelta(info, pipChange);
+        final int delta = getFixedRotationDelta(info, pipChange, mPipDisplayLayoutState);
         if (delta != ROTATION_0) {
             // Update transition target changes in place to prepare for fixed rotation.
             handleBoundsEnterFixedRotation(info, pipChange, pipActivityChange);
@@ -582,27 +597,6 @@ public class PipTransition extends PipTransitionController implements
                 endBounds.top + activityEndOffset.y);
     }
 
-    private void handleExpandFixedRotation(TransitionInfo.Change outPipTaskChange, int delta) {
-        final Rect endBounds = outPipTaskChange.getEndAbsBounds();
-        final int width = endBounds.width();
-        final int height = endBounds.height();
-        final int left = endBounds.left;
-        final int top = endBounds.top;
-        int newTop, newLeft;
-
-        if (delta == Surface.ROTATION_90) {
-            newLeft = top;
-            newTop = -(left + width);
-        } else {
-            newLeft = -(height + top);
-            newTop = left;
-        }
-        // Modify the endBounds, rotating and placing them potentially off-screen, so that
-        // as we translate and rotate around the origin, we place them right into the target.
-        endBounds.set(newLeft, newTop, newLeft + height, newTop + width);
-    }
-
-
     private boolean startAlphaTypeEnterAnimation(@NonNull TransitionInfo info,
             @NonNull SurfaceControl.Transaction startTransaction,
             @NonNull SurfaceControl.Transaction finishTransaction,
@@ -630,83 +624,6 @@ public class PipTransition extends PipTransitionController implements
         return true;
     }
 
-    private boolean startExpandAnimation(@NonNull TransitionInfo info,
-            @NonNull SurfaceControl.Transaction startTransaction,
-            @NonNull SurfaceControl.Transaction finishTransaction,
-            @NonNull Transitions.TransitionFinishCallback finishCallback) {
-        WindowContainerToken pipToken = mPipTransitionState.getPipTaskToken();
-
-        TransitionInfo.Change pipChange = getChangeByToken(info, pipToken);
-        if (pipChange == null) {
-            // pipChange is null, check to see if we've reparented the PIP activity for
-            // the multi activity case. If so we should use the activity leash instead
-            for (TransitionInfo.Change change : info.getChanges()) {
-                if (change.getTaskInfo() == null
-                        && change.getLastParent() != null
-                        && change.getLastParent().equals(pipToken)) {
-                    pipChange = change;
-                    break;
-                }
-            }
-
-            // failsafe
-            if (pipChange == null) {
-                return false;
-            }
-        }
-        mFinishCallback = finishCallback;
-
-        // The parent change if we were in a multi-activity PiP; null if single activity PiP.
-        final TransitionInfo.Change parentBeforePip = pipChange.getTaskInfo() == null
-                ? getChangeByToken(info, pipChange.getParent()) : null;
-        if (parentBeforePip != null) {
-            // For multi activity, we need to manually set the leash layer
-            startTransaction.setLayer(parentBeforePip.getLeash(), Integer.MAX_VALUE - 1);
-        }
-
-        final Rect startBounds = pipChange.getStartAbsBounds();
-        final Rect endBounds = pipChange.getEndAbsBounds();
-        final SurfaceControl pipLeash = getLeash(pipChange);
-
-        PictureInPictureParams params = null;
-        if (pipChange.getTaskInfo() != null) {
-            // single activity
-            params = getPipParams(pipChange);
-        } else if (parentBeforePip != null && parentBeforePip.getTaskInfo() != null) {
-            // multi activity
-            params = getPipParams(parentBeforePip);
-        }
-        final Rect sourceRectHint = PipBoundsAlgorithm.getValidSourceHintRect(params, endBounds,
-                startBounds);
-
-        // We define delta = startRotation - endRotation, so we need to flip the sign.
-        final int delta = -getFixedRotationDelta(info, pipChange);
-        if (delta != ROTATION_0) {
-            // Update PiP target change in place to prepare for fixed rotation;
-            handleExpandFixedRotation(pipChange, delta);
-        }
-
-        PipExpandAnimator animator = new PipExpandAnimator(mContext, pipLeash,
-                startTransaction, finishTransaction, endBounds, startBounds, endBounds,
-                sourceRectHint, delta);
-        animator.setAnimationEndCallback(() -> {
-            if (parentBeforePip != null) {
-                // TODO b/377362511: Animate local leash instead to also handle letterbox case.
-                // For multi-activity, set the crop to be null
-                finishTransaction.setCrop(pipLeash, null);
-            }
-            finishTransition();
-        });
-        cacheAndStartTransitionAnimator(animator);
-
-        // Save the PiP bounds in case, we re-enter the PiP with the same component.
-        float snapFraction = mPipBoundsAlgorithm.getSnapFraction(
-                mPipBoundsState.getBounds());
-        mPipBoundsState.saveReentryState(snapFraction);
-
-        return true;
-    }
-
     private boolean startRemoveAnimation(@NonNull TransitionInfo info,
             @NonNull SurfaceControl.Transaction startTransaction,
             @NonNull SurfaceControl.Transaction finishTransaction,
@@ -740,29 +657,6 @@ public class PipTransition extends PipTransitionController implements
     // Various helpers to resolve transition requests and infos
     //
 
-    @Nullable
-    private TransitionInfo.Change getPipChange(TransitionInfo info) {
-        for (TransitionInfo.Change change : info.getChanges()) {
-            if (change.getTaskInfo() != null
-                    && change.getTaskInfo().getWindowingMode() == WINDOWING_MODE_PINNED) {
-                return change;
-            }
-        }
-        return null;
-    }
-
-    @Nullable
-    private TransitionInfo.Change getChangeByToken(TransitionInfo info,
-            WindowContainerToken token) {
-        for (TransitionInfo.Change change : info.getChanges()) {
-            if (change.getTaskInfo() != null
-                    && change.getTaskInfo().getToken().equals(token)) {
-                return change;
-            }
-        }
-        return null;
-    }
-
     @NonNull
     private Rect getAdjustedSourceRectHint(@NonNull TransitionInfo info,
             @NonNull TransitionInfo.Change pipTaskChange,
@@ -786,8 +680,8 @@ public class PipTransition extends PipTransitionController implements
             Rect cutoutInsets = parentBeforePip != null
                     ? parentBeforePip.getTaskInfo().displayCutoutInsets
                     : pipTaskChange.getTaskInfo().displayCutoutInsets;
-            if (cutoutInsets != null
-                    && getFixedRotationDelta(info, pipTaskChange) == ROTATION_90) {
+            if (cutoutInsets != null && getFixedRotationDelta(info, pipTaskChange,
+                    mPipDisplayLayoutState) == ROTATION_90) {
                 adjustedSourceRectHint.offset(cutoutInsets.left, cutoutInsets.top);
             }
             if (mPipDesktopState.isDesktopWindowingPipEnabled()) {
@@ -804,25 +698,6 @@ public class PipTransition extends PipTransitionController implements
         return adjustedSourceRectHint;
     }
 
-    @Surface.Rotation
-    private int getFixedRotationDelta(@NonNull TransitionInfo info,
-            @NonNull TransitionInfo.Change pipChange) {
-        TransitionInfo.Change fixedRotationChange = findFixedRotationChange(info);
-        int startRotation = pipChange.getStartRotation();
-        if (pipChange.getEndRotation() != ROTATION_UNDEFINED
-                && startRotation != pipChange.getEndRotation()) {
-            // If PiP change was collected along with the display change and the orientation change
-            // happened in sync with the PiP change, then do not treat this as fixed-rotation case.
-            return ROTATION_0;
-        }
-
-        int endRotation = fixedRotationChange != null
-                ? fixedRotationChange.getEndFixedRotation() : mPipDisplayLayoutState.getRotation();
-        int delta = endRotation == ROTATION_UNDEFINED ? ROTATION_0
-                : startRotation - endRotation;
-        return delta;
-    }
-
     private void prepareOtherTargetTransforms(TransitionInfo info,
             SurfaceControl.Transaction startTransaction,
             SurfaceControl.Transaction finishTransaction) {
@@ -1009,20 +884,6 @@ public class PipTransition extends PipTransitionController implements
         mTransitionAnimator.start();
     }
 
-    @NonNull
-    private static PictureInPictureParams getPipParams(@NonNull TransitionInfo.Change pipChange) {
-        return pipChange.getTaskInfo().pictureInPictureParams != null
-                ? pipChange.getTaskInfo().pictureInPictureParams
-                : new PictureInPictureParams.Builder().build();
-    }
-
-    @NonNull
-    private static SurfaceControl getLeash(TransitionInfo.Change change) {
-        SurfaceControl leash = change.getLeash();
-        Preconditions.checkNotNull(leash, "Leash is null for change=" + change);
-        return leash;
-    }
-
     //
     // Miscellaneous callbacks and listeners
     //
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransitionState.java b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransitionState.java
index 8805cbb0dfbd..18c9a705dcf7 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransitionState.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/PipTransitionState.java
@@ -314,7 +314,8 @@ public class PipTransitionState {
         mSwipePipToHomeAppBounds.setEmpty();
     }
 
-    @Nullable WindowContainerToken getPipTaskToken() {
+    @Nullable
+    public WindowContainerToken getPipTaskToken() {
         return mPipTaskInfo != null ? mPipTaskInfo.getToken() : null;
     }
 
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/transition/PipExpandHandler.java b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/transition/PipExpandHandler.java
new file mode 100644
index 000000000000..db4942b2fb95
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/transition/PipExpandHandler.java
@@ -0,0 +1,331 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.wm.shell.pip2.phone.transition;
+
+import static android.view.Surface.ROTATION_0;
+
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getChangeByToken;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getFixedRotationDelta;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getLeash;
+import static com.android.wm.shell.pip2.phone.transition.PipTransitionUtils.getPipParams;
+import static com.android.wm.shell.transition.Transitions.TRANSIT_EXIT_PIP;
+import static com.android.wm.shell.transition.Transitions.TRANSIT_EXIT_PIP_TO_SPLIT;
+
+import android.animation.ValueAnimator;
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.app.PictureInPictureParams;
+import android.content.Context;
+import android.graphics.Rect;
+import android.os.IBinder;
+import android.view.Surface;
+import android.view.SurfaceControl;
+import android.window.TransitionInfo;
+import android.window.TransitionRequestInfo;
+import android.window.WindowContainerToken;
+import android.window.WindowContainerTransaction;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.protolog.ProtoLog;
+import com.android.wm.shell.common.pip.PipBoundsAlgorithm;
+import com.android.wm.shell.common.pip.PipBoundsState;
+import com.android.wm.shell.common.pip.PipDisplayLayoutState;
+import com.android.wm.shell.pip2.animation.PipExpandAnimator;
+import com.android.wm.shell.pip2.phone.PipTransitionState;
+import com.android.wm.shell.protolog.ShellProtoLogGroup;
+import com.android.wm.shell.splitscreen.SplitScreenController;
+import com.android.wm.shell.transition.Transitions;
+
+import java.util.Optional;
+
+public class PipExpandHandler implements Transitions.TransitionHandler {
+    private final Context mContext;
+    private final PipBoundsState mPipBoundsState;
+    private final PipBoundsAlgorithm mPipBoundsAlgorithm;
+    private final PipTransitionState mPipTransitionState;
+    private final PipDisplayLayoutState mPipDisplayLayoutState;
+    private final Optional<SplitScreenController> mSplitScreenControllerOptional;
+
+    @Nullable
+    private Transitions.TransitionFinishCallback mFinishCallback;
+    @Nullable
+    private ValueAnimator mTransitionAnimator;
+
+    private PipExpandAnimatorSupplier mPipExpandAnimatorSupplier;
+
+    public PipExpandHandler(Context context,
+            PipBoundsState pipBoundsState,
+            PipBoundsAlgorithm pipBoundsAlgorithm,
+            PipTransitionState pipTransitionState,
+            PipDisplayLayoutState pipDisplayLayoutState,
+            Optional<SplitScreenController> splitScreenControllerOptional) {
+        mContext = context;
+        mPipBoundsState = pipBoundsState;
+        mPipBoundsAlgorithm = pipBoundsAlgorithm;
+        mPipTransitionState = pipTransitionState;
+        mPipDisplayLayoutState = pipDisplayLayoutState;
+        mSplitScreenControllerOptional = splitScreenControllerOptional;
+
+        mPipExpandAnimatorSupplier = PipExpandAnimator::new;
+    }
+
+    @Override
+    public WindowContainerTransaction handleRequest(@NonNull IBinder transition,
+            @NonNull TransitionRequestInfo request) {
+        // All Exit-via-Expand from PiP transitions are Shell initiated.
+        return null;
+    }
+
+    @Override
+    public boolean startAnimation(@NonNull IBinder transition,
+            @NonNull TransitionInfo info,
+            @NonNull SurfaceControl.Transaction startTransaction,
+            @NonNull SurfaceControl.Transaction finishTransaction,
+            @NonNull Transitions.TransitionFinishCallback finishCallback) {
+        switch (info.getType()) {
+            case TRANSIT_EXIT_PIP:
+                return startExpandAnimation(info, startTransaction, finishTransaction,
+                        finishCallback);
+            case TRANSIT_EXIT_PIP_TO_SPLIT:
+                return startExpandToSplitAnimation(info, startTransaction, finishTransaction,
+                        finishCallback);
+        }
+        return false;
+    }
+
+    @Override
+    public void mergeAnimation(@NonNull IBinder transition, @NonNull TransitionInfo info,
+            @NonNull SurfaceControl.Transaction t, @NonNull IBinder mergeTarget,
+            @NonNull Transitions.TransitionFinishCallback finishCallback) {
+        end();
+    }
+
+    /**
+     * Ends the animation if such is running in the context of expanding out of PiP.
+     */
+    public void end() {
+        if (mTransitionAnimator != null && mTransitionAnimator.isRunning()) {
+            mTransitionAnimator.end();
+            mTransitionAnimator = null;
+        }
+    }
+
+    private boolean startExpandAnimation(@NonNull TransitionInfo info,
+            @NonNull SurfaceControl.Transaction startTransaction,
+            @NonNull SurfaceControl.Transaction finishTransaction,
+            @NonNull Transitions.TransitionFinishCallback finishCallback) {
+        WindowContainerToken pipToken = mPipTransitionState.getPipTaskToken();
+
+        TransitionInfo.Change pipChange = getChangeByToken(info, pipToken);
+        if (pipChange == null) {
+            // pipChange is null, check to see if we've reparented the PIP activity for
+            // the multi activity case. If so we should use the activity leash instead
+            for (TransitionInfo.Change change : info.getChanges()) {
+                if (change.getTaskInfo() == null
+                        && change.getLastParent() != null
+                        && change.getLastParent().equals(pipToken)) {
+                    pipChange = change;
+                    break;
+                }
+            }
+
+            // failsafe
+            if (pipChange == null) {
+                return false;
+            }
+        }
+        mFinishCallback = finishCallback;
+
+        // The parent change if we were in a multi-activity PiP; null if single activity PiP.
+        final TransitionInfo.Change parentBeforePip = pipChange.getTaskInfo() == null
+                ? getChangeByToken(info, pipChange.getParent()) : null;
+        if (parentBeforePip != null) {
+            // For multi activity, we need to manually set the leash layer
+            startTransaction.setLayer(parentBeforePip.getLeash(), Integer.MAX_VALUE - 1);
+        }
+
+        final Rect startBounds = pipChange.getStartAbsBounds();
+        final Rect endBounds = pipChange.getEndAbsBounds();
+        final SurfaceControl pipLeash = getLeash(pipChange);
+
+        PictureInPictureParams params = null;
+        if (pipChange.getTaskInfo() != null) {
+            // single activity
+            params = getPipParams(pipChange);
+        } else if (parentBeforePip != null && parentBeforePip.getTaskInfo() != null) {
+            // multi activity
+            params = getPipParams(parentBeforePip);
+        }
+        final Rect sourceRectHint = PipBoundsAlgorithm.getValidSourceHintRect(params, endBounds,
+                startBounds);
+
+        // We define delta = startRotation - endRotation, so we need to flip the sign.
+        final int delta = -getFixedRotationDelta(info, pipChange, mPipDisplayLayoutState);
+        if (delta != ROTATION_0) {
+            // Update PiP target change in place to prepare for fixed rotation;
+            handleExpandFixedRotation(pipChange, delta);
+        }
+
+        PipExpandAnimator animator = mPipExpandAnimatorSupplier.get(mContext, pipLeash,
+                startTransaction, finishTransaction, endBounds, startBounds, endBounds,
+                sourceRectHint, delta);
+        animator.setAnimationEndCallback(() -> {
+            if (parentBeforePip != null) {
+                // TODO b/377362511: Animate local leash instead to also handle letterbox case.
+                // For multi-activity, set the crop to be null
+                finishTransaction.setCrop(pipLeash, null);
+            }
+            finishTransition();
+        });
+        cacheAndStartTransitionAnimator(animator);
+        saveReentryState();
+        return true;
+    }
+
+    private boolean startExpandToSplitAnimation(@NonNull TransitionInfo info,
+            @NonNull SurfaceControl.Transaction startTransaction,
+            @NonNull SurfaceControl.Transaction finishTransaction,
+            @NonNull Transitions.TransitionFinishCallback finishCallback) {
+        WindowContainerToken pipToken = mPipTransitionState.getPipTaskToken();
+
+        // Expanding PiP to Split-screen makes sense only if we are dealing with multi-activity PiP
+        // and the lastParentBeforePip is still in one of the split-stages.
+        //
+        // This means we should be animating the PiP activity leash, since we do the reparenting
+        // of the PiP activity back to its original task in startWCT.
+        TransitionInfo.Change pipChange = null;
+        for (TransitionInfo.Change change : info.getChanges()) {
+            if (change.getTaskInfo() == null
+                    && change.getLastParent() != null
+                    && change.getLastParent().equals(pipToken)) {
+                pipChange = change;
+                break;
+            }
+        }
+        // failsafe
+        if (pipChange == null || pipChange.getLeash() == null) {
+            return false;
+        }
+        mFinishCallback = finishCallback;
+
+        // Get the original parent before PiP. If original task hosting the PiP activity was
+        // already visible, then it's not participating in this transition; in that case,
+        // parentBeforePip would be null.
+        final TransitionInfo.Change parentBeforePip = getChangeByToken(info, pipChange.getParent());
+
+        final Rect startBounds = pipChange.getStartAbsBounds();
+        final Rect endBounds = pipChange.getEndAbsBounds();
+        if (parentBeforePip != null) {
+            // Since we have the parent task amongst the targets, all PiP activity
+            // leash translations will be relative to the original task, NOT the root leash.
+            startBounds.offset(-parentBeforePip.getStartAbsBounds().left,
+                    -parentBeforePip.getStartAbsBounds().top);
+            endBounds.offset(-parentBeforePip.getEndAbsBounds().left,
+                    -parentBeforePip.getEndAbsBounds().top);
+        }
+
+        final SurfaceControl pipLeash = pipChange.getLeash();
+        PipExpandAnimator animator = mPipExpandAnimatorSupplier.get(mContext, pipLeash,
+                startTransaction, finishTransaction, endBounds, startBounds, endBounds,
+                null /* srcRectHint */, ROTATION_0 /* delta */);
+
+
+        mSplitScreenControllerOptional.ifPresent(splitController -> {
+            splitController.finishEnterSplitScreen(finishTransaction);
+        });
+
+        animator.setAnimationEndCallback(() -> {
+            if (parentBeforePip == null) {
+                // After PipExpandAnimator is done modifying finishTransaction, we need to make
+                // sure PiP activity leash is offset at origin relative to its task as we reparent
+                // targets back from the transition root leash.
+                finishTransaction.setPosition(pipLeash, 0, 0);
+            }
+            finishTransition();
+        });
+        cacheAndStartTransitionAnimator(animator);
+        saveReentryState();
+        return true;
+    }
+
+    private void finishTransition() {
+        final int currentState = mPipTransitionState.getState();
+        if (currentState != PipTransitionState.EXITING_PIP) {
+            ProtoLog.e(ShellProtoLogGroup.WM_SHELL_PICTURE_IN_PICTURE,
+                    "Unexpected state %s as we are finishing an exit-via-expand transition",
+                    mPipTransitionState);
+        }
+        mPipTransitionState.setState(PipTransitionState.EXITED_PIP);
+
+        if (mFinishCallback != null) {
+            // Need to unset mFinishCallback first because onTransitionFinished can re-enter this
+            // handler if there is a pending PiP animation.
+            final Transitions.TransitionFinishCallback finishCallback = mFinishCallback;
+            mFinishCallback = null;
+            finishCallback.onTransitionFinished(null /* finishWct */);
+        }
+    }
+
+    private void handleExpandFixedRotation(TransitionInfo.Change outPipTaskChange, int delta) {
+        final Rect endBounds = outPipTaskChange.getEndAbsBounds();
+        final int width = endBounds.width();
+        final int height = endBounds.height();
+        final int left = endBounds.left;
+        final int top = endBounds.top;
+        int newTop, newLeft;
+
+        if (delta == Surface.ROTATION_90) {
+            newLeft = top;
+            newTop = -(left + width);
+        } else {
+            newLeft = -(height + top);
+            newTop = left;
+        }
+        // Modify the endBounds, rotating and placing them potentially off-screen, so that
+        // as we translate and rotate around the origin, we place them right into the target.
+        endBounds.set(newLeft, newTop, newLeft + height, newTop + width);
+    }
+
+    private void saveReentryState() {
+        float snapFraction = mPipBoundsAlgorithm.getSnapFraction(
+                mPipBoundsState.getBounds());
+        mPipBoundsState.saveReentryState(snapFraction);
+    }
+
+    private void cacheAndStartTransitionAnimator(@NonNull ValueAnimator animator) {
+        mTransitionAnimator = animator;
+        mTransitionAnimator.start();
+    }
+
+    @VisibleForTesting
+    interface PipExpandAnimatorSupplier {
+        PipExpandAnimator get(Context context,
+                @NonNull SurfaceControl leash,
+                SurfaceControl.Transaction startTransaction,
+                SurfaceControl.Transaction finishTransaction,
+                @NonNull Rect baseBounds,
+                @NonNull Rect startBounds,
+                @NonNull Rect endBounds,
+                @Nullable Rect sourceRectHint,
+                @Surface.Rotation int rotation);
+    }
+
+    @VisibleForTesting
+    void setPipExpandAnimatorSupplier(@NonNull PipExpandAnimatorSupplier supplier) {
+        mPipExpandAnimatorSupplier = supplier;
+    }
+}
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/transition/PipTransitionUtils.java b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/transition/PipTransitionUtils.java
new file mode 100644
index 000000000000..01cda6c91108
--- /dev/null
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/pip2/phone/transition/PipTransitionUtils.java
@@ -0,0 +1,133 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.wm.shell.pip2.phone.transition;
+
+import static android.app.WindowConfiguration.ROTATION_UNDEFINED;
+import static android.app.WindowConfiguration.WINDOWING_MODE_PINNED;
+import static android.view.Surface.ROTATION_0;
+
+import android.annotation.NonNull;
+import android.app.PictureInPictureParams;
+import android.view.Surface;
+import android.view.SurfaceControl;
+import android.window.TransitionInfo;
+import android.window.WindowContainerToken;
+
+import androidx.annotation.Nullable;
+
+import com.android.internal.util.Preconditions;
+import com.android.wm.shell.common.pip.PipDisplayLayoutState;
+
+/**
+ * A set of utility methods to help resolve PiP transitions.
+ */
+public class PipTransitionUtils {
+
+    /**
+     * @return change for a pinned mode task; null if no such task is in the list of changes.
+     */
+    @Nullable
+    public static TransitionInfo.Change getPipChange(TransitionInfo info) {
+        for (TransitionInfo.Change change : info.getChanges()) {
+            if (change.getTaskInfo() != null
+                    && change.getTaskInfo().getWindowingMode() == WINDOWING_MODE_PINNED) {
+                return change;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * @return change for a task with the provided token; null if no task with such token found.
+     */
+    @Nullable
+    public static TransitionInfo.Change getChangeByToken(TransitionInfo info,
+            WindowContainerToken token) {
+        for (TransitionInfo.Change change : info.getChanges()) {
+            if (change.getTaskInfo() != null
+                    && change.getTaskInfo().getToken().equals(token)) {
+                return change;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * @return the leash to interact with the container this change represents.
+     * @throws NullPointerException if the leash is null.
+     */
+    @NonNull
+    public static SurfaceControl getLeash(TransitionInfo.Change change) {
+        SurfaceControl leash = change.getLeash();
+        Preconditions.checkNotNull(leash, "Leash is null for change=" + change);
+        return leash;
+    }
+
+    /**
+     * Get the rotation delta in a potential fixed rotation transition.
+     *
+     * Whenever PiP participates in fixed rotation, its actual orientation isn't updated
+     * in the initial transition as per the async rotation convention.
+     *
+     * @param pipChange PiP change to verify that PiP task's rotation wasn't updated already.
+     * @param pipDisplayLayoutState display layout state that PiP component keeps track of.
+     */
+    @Surface.Rotation
+    public static int getFixedRotationDelta(@NonNull TransitionInfo info,
+            @NonNull TransitionInfo.Change pipChange,
+            @NonNull PipDisplayLayoutState pipDisplayLayoutState) {
+        TransitionInfo.Change fixedRotationChange = findFixedRotationChange(info);
+        int startRotation = pipChange.getStartRotation();
+        if (pipChange.getEndRotation() != ROTATION_UNDEFINED
+                && startRotation != pipChange.getEndRotation()) {
+            // If PiP change was collected along with the display change and the orientation change
+            // happened in sync with the PiP change, then do not treat this as fixed-rotation case.
+            return ROTATION_0;
+        }
+
+        int endRotation = fixedRotationChange != null
+                ? fixedRotationChange.getEndFixedRotation() : pipDisplayLayoutState.getRotation();
+        int delta = endRotation == ROTATION_UNDEFINED ? ROTATION_0
+                : startRotation - endRotation;
+        return delta;
+    }
+
+    /**
+     * Gets a change amongst the transition targets that is in a different final orientation than
+     * the display, signalling a potential fixed rotation transition.
+     */
+    @Nullable
+    public static TransitionInfo.Change findFixedRotationChange(@NonNull TransitionInfo info) {
+        for (int i = info.getChanges().size() - 1; i >= 0; --i) {
+            final TransitionInfo.Change change = info.getChanges().get(i);
+            if (change.getEndFixedRotation() != ROTATION_UNDEFINED) {
+                return change;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * @return {@link PictureInPictureParams} provided by the client from the PiP change.
+     */
+    @NonNull
+    public static PictureInPictureParams getPipParams(@NonNull TransitionInfo.Change pipChange) {
+        return pipChange.getTaskInfo().pictureInPictureParams != null
+                ? pipChange.getTaskInfo().pictureInPictureParams
+                : new PictureInPictureParams.Builder().build();
+    }
+}
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/PipSchedulerTest.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/PipSchedulerTest.java
index 8e0381e4f933..0c1952910d1a 100644
--- a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/PipSchedulerTest.java
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/PipSchedulerTest.java
@@ -19,6 +19,7 @@ package com.android.wm.shell.pip2.phone;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.when;
@@ -26,6 +27,7 @@ import static org.mockito.kotlin.MatchersKt.eq;
 import static org.mockito.kotlin.VerificationKt.times;
 import static org.mockito.kotlin.VerificationKt.verify;
 
+import android.app.ActivityManager;
 import android.content.Context;
 import android.content.res.Resources;
 import android.graphics.Matrix;
@@ -44,15 +46,19 @@ import com.android.wm.shell.common.pip.PipDesktopState;
 import com.android.wm.shell.pip.PipTransitionController;
 import com.android.wm.shell.pip2.PipSurfaceTransactionHelper;
 import com.android.wm.shell.pip2.animation.PipAlphaAnimator;
+import com.android.wm.shell.splitscreen.SplitScreenController;
 
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
+import org.mockito.ArgumentMatchers;
 import org.mockito.Captor;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import java.util.Optional;
+
 /**
  * Unit test against {@link PipScheduler}
  */
@@ -77,6 +83,8 @@ public class PipSchedulerTest {
     @Mock private PipSurfaceTransactionHelper.SurfaceControlTransactionFactory mMockFactory;
     @Mock private SurfaceControl.Transaction mMockTransaction;
     @Mock private PipAlphaAnimator mMockAlphaAnimator;
+    @Mock private SplitScreenController mMockSplitScreenController;
+
     @Captor private ArgumentCaptor<Runnable> mRunnableArgumentCaptor;
     @Captor private ArgumentCaptor<WindowContainerTransaction> mWctArgumentCaptor;
 
@@ -93,7 +101,8 @@ public class PipSchedulerTest {
                 .thenReturn(mMockTransaction);
 
         mPipScheduler = new PipScheduler(mMockContext, mMockPipBoundsState, mMockMainExecutor,
-                mMockPipTransitionState, mMockPipDesktopState);
+                mMockPipTransitionState, Optional.of(mMockSplitScreenController),
+                mMockPipDesktopState);
         mPipScheduler.setPipTransitionController(mMockPipTransitionController);
         mPipScheduler.setSurfaceControlTransactionFactory(mMockFactory);
         mPipScheduler.setPipAlphaAnimatorSupplier((context, leash, startTx, finishTx, direction) ->
@@ -119,12 +128,18 @@ public class PipSchedulerTest {
         assertNotNull(mRunnableArgumentCaptor.getValue());
         mRunnableArgumentCaptor.getValue().run();
 
-        verify(mMockPipTransitionController, never()).startExpandTransition(any());
+        verify(mMockPipTransitionController, never()).startExpandTransition(any(), anyBoolean());
     }
 
     @Test
-    public void scheduleExitPipViaExpand_exitTransitionCalled() {
+    public void scheduleExitPipViaExpand_noSplit_expandTransitionCalled() {
         setMockPipTaskToken();
+        ActivityManager.RunningTaskInfo pipTaskInfo = getTaskInfoWithLastParentBeforePip(1);
+        when(mMockPipTransitionState.getPipTaskInfo()).thenReturn(pipTaskInfo);
+
+        // Make sure task with the id = 1 isn't in split-screen.
+        when(mMockSplitScreenController.isTaskInSplitScreen(
+                ArgumentMatchers.eq(1))).thenReturn(false);
 
         mPipScheduler.scheduleExitPipViaExpand();
 
@@ -132,7 +147,29 @@ public class PipSchedulerTest {
         assertNotNull(mRunnableArgumentCaptor.getValue());
         mRunnableArgumentCaptor.getValue().run();
 
-        verify(mMockPipTransitionController, times(1)).startExpandTransition(any());
+        verify(mMockPipTransitionController, times(1)).startExpandTransition(any(), anyBoolean());
+    }
+
+    @Test
+    public void scheduleExitPipViaExpand_lastParentInSplit_prepareSplitAndExpand() {
+        setMockPipTaskToken();
+        ActivityManager.RunningTaskInfo pipTaskInfo = getTaskInfoWithLastParentBeforePip(1);
+        when(mMockPipTransitionState.getPipTaskInfo()).thenReturn(pipTaskInfo);
+
+        // Make sure task with the id = 1 is in split-screen.
+        when(mMockSplitScreenController.isTaskInSplitScreen(
+                ArgumentMatchers.eq(1))).thenReturn(true);
+
+        mPipScheduler.scheduleExitPipViaExpand();
+
+        verify(mMockMainExecutor, times(1)).execute(mRunnableArgumentCaptor.capture());
+        assertNotNull(mRunnableArgumentCaptor.getValue());
+        mRunnableArgumentCaptor.getValue().run();
+
+        // We need to both prepare the split screen with the last parent and start expanding.
+        verify(mMockSplitScreenController,
+                times(1)).prepareEnterSplitScreen(any(), any(), anyInt());
+        verify(mMockPipTransitionController, times(1)).startExpandTransition(any(), anyBoolean());
     }
 
     @Test
@@ -259,4 +296,10 @@ public class PipSchedulerTest {
     private void setMockPipTaskToken() {
         when(mMockPipTransitionState.getPipTaskToken()).thenReturn(mMockPipTaskToken);
     }
+
+    private ActivityManager.RunningTaskInfo getTaskInfoWithLastParentBeforePip(int lastParentId) {
+        final ActivityManager.RunningTaskInfo taskInfo = new ActivityManager.RunningTaskInfo();
+        taskInfo.lastParentTaskIdBeforePip = lastParentId;
+        return taskInfo;
+    }
 }
diff --git a/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/transition/PipExpandHandlerTest.java b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/transition/PipExpandHandlerTest.java
new file mode 100644
index 000000000000..2a22842eda1a
--- /dev/null
+++ b/libs/WindowManager/Shell/tests/unittest/src/com/android/wm/shell/pip2/phone/transition/PipExpandHandlerTest.java
@@ -0,0 +1,188 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.wm.shell.pip2.phone.transition;
+
+import static android.app.WindowConfiguration.WINDOWING_MODE_FULLSCREEN;
+import static android.view.WindowManager.TRANSIT_CHANGE;
+
+import static com.android.wm.shell.transition.Transitions.TRANSIT_EXIT_PIP;
+import static com.android.wm.shell.transition.Transitions.TRANSIT_EXIT_PIP_TO_SPLIT;
+
+import static org.junit.Assert.assertNull;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+import static org.mockito.kotlin.VerificationKt.times;
+import static org.mockito.kotlin.VerificationKt.verify;
+
+import android.annotation.Nullable;
+import android.app.ActivityManager;
+import android.app.PictureInPictureParams;
+import android.app.WindowConfiguration;
+import android.content.Context;
+import android.content.Intent;
+import android.graphics.Rect;
+import android.os.IBinder;
+import android.testing.AndroidTestingRunner;
+import android.testing.TestableLooper;
+import android.view.Surface;
+import android.view.SurfaceControl;
+import android.view.WindowManager;
+import android.window.TransitionInfo;
+import android.window.TransitionRequestInfo;
+import android.window.WindowContainerToken;
+import android.window.WindowContainerTransaction;
+
+import androidx.test.filters.SmallTest;
+
+import com.android.wm.shell.common.pip.PipBoundsAlgorithm;
+import com.android.wm.shell.common.pip.PipBoundsState;
+import com.android.wm.shell.common.pip.PipDisplayLayoutState;
+import com.android.wm.shell.pip2.animation.PipExpandAnimator;
+import com.android.wm.shell.pip2.phone.PipTransitionState;
+import com.android.wm.shell.splitscreen.SplitScreenController;
+import com.android.wm.shell.transition.TransitionInfoBuilder;
+import com.android.wm.shell.util.StubTransaction;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import java.util.Optional;
+
+/**
+ * Unit test against {@link PipExpandHandler}
+ */
+
+@SmallTest
+@TestableLooper.RunWithLooper
+@RunWith(AndroidTestingRunner.class)
+public class PipExpandHandlerTest {
+    @Mock private Context mMockContext;
+    @Mock private PipBoundsState mMockPipBoundsState;
+    @Mock private PipBoundsAlgorithm mMockPipBoundsAlgorithm;
+    @Mock private PipTransitionState mMockPipTransitionState;
+    @Mock private PipDisplayLayoutState mMockPipDisplayLayoutState;
+    @Mock private SplitScreenController mMockSplitScreenController;
+
+    @Mock private IBinder mMockTransitionToken;
+    @Mock private TransitionRequestInfo mMockRequestInfo;
+    @Mock private StubTransaction mStartT;
+    @Mock private StubTransaction mFinishT;
+    @Mock private SurfaceControl mPipLeash;
+
+    @Mock private PipExpandAnimator mMockPipExpandAnimator;
+
+    @Surface.Rotation
+    private static final int DISPLAY_ROTATION = Surface.ROTATION_0;
+
+    private static final float SNAP_FRACTION = 1.5f;
+    private static final Rect PIP_BOUNDS = new Rect(0, 0, 100, 100);
+    private static final Rect DISPLAY_BOUNDS = new Rect(0, 0, 1000, 1000);
+    private static final Rect RIGHT_HALF_DISPLAY_BOUNDS = new Rect(500, 0, 1000, 1000);
+
+    private PipExpandHandler mPipExpandHandler;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+        when(mMockPipBoundsState.getBounds()).thenReturn(PIP_BOUNDS);
+        when(mMockPipBoundsAlgorithm.getSnapFraction(eq(PIP_BOUNDS))).thenReturn(SNAP_FRACTION);
+        when(mMockPipDisplayLayoutState.getRotation()).thenReturn(DISPLAY_ROTATION);
+
+        mPipExpandHandler = new PipExpandHandler(mMockContext, mMockPipBoundsState,
+                mMockPipBoundsAlgorithm, mMockPipTransitionState, mMockPipDisplayLayoutState,
+                Optional.of(mMockSplitScreenController));
+        mPipExpandHandler.setPipExpandAnimatorSupplier((context, leash, startTransaction,
+                finishTransaction, baseBounds, startBounds, endBounds,
+                sourceRectHint, rotation) -> mMockPipExpandAnimator);
+    }
+
+    @Test
+    public void handleRequest_returnNull() {
+        // All expand from PiP transitions are started in Shell, so handleRequest shouldn't be
+        // returning any non-null WCT
+        WindowContainerTransaction wct = mPipExpandHandler.handleRequest(
+                mMockTransitionToken, mMockRequestInfo);
+        assertNull(wct);
+    }
+
+    @Test
+    public void startAnimation_transitExit_startExpandAnimator() {
+        final ActivityManager.RunningTaskInfo pipTaskInfo = createPipTaskInfo(
+                1, WINDOWING_MODE_FULLSCREEN, new PictureInPictureParams.Builder().build());
+
+        final TransitionInfo info = getExpandFromPipTransitionInfo(
+                TRANSIT_EXIT_PIP, pipTaskInfo, null /* lastParent */, false /* toSplit */);
+        final WindowContainerToken pipToken = pipTaskInfo.getToken();
+        when(mMockPipTransitionState.getPipTaskToken()).thenReturn(pipToken);
+
+        mPipExpandHandler.startAnimation(mMockTransitionToken, info, mStartT, mFinishT,
+                (wct) -> {});
+
+        verify(mMockPipExpandAnimator, times(1)).start();
+        verify(mMockPipBoundsState, times(1)).saveReentryState(SNAP_FRACTION);
+    }
+
+    @Test
+    public void startAnimation_transitExitToSplit_startExpandAnimator() {
+        // The task info of the task that was pinned while we were in PiP.
+        final WindowContainerToken pipToken = createPipTaskInfo(1, WINDOWING_MODE_FULLSCREEN,
+                new PictureInPictureParams.Builder().build()).getToken();
+        when(mMockPipTransitionState.getPipTaskToken()).thenReturn(pipToken);
+
+        // Change representing the ActivityRecord we are animating in the multi-activity PiP case;
+        // make sure change's taskInfo=null as this is an activity, but let lastParent be PiP token.
+        final TransitionInfo info = getExpandFromPipTransitionInfo(
+                TRANSIT_EXIT_PIP_TO_SPLIT, null /* taskInfo */, pipToken, true /* toSplit */);
+
+        mPipExpandHandler.startAnimation(mMockTransitionToken, info, mStartT, mFinishT,
+                (wct) -> {});
+
+        verify(mMockSplitScreenController, times(1)).finishEnterSplitScreen(eq(mFinishT));
+        verify(mMockPipExpandAnimator, times(1)).start();
+        verify(mMockPipBoundsState, times(1)).saveReentryState(SNAP_FRACTION);
+    }
+
+    private TransitionInfo getExpandFromPipTransitionInfo(@WindowManager.TransitionType int type,
+            @Nullable ActivityManager.RunningTaskInfo pipTaskInfo,
+            @Nullable WindowContainerToken lastParent, boolean toSplit) {
+        final TransitionInfo info = new TransitionInfoBuilder(type)
+                .addChange(TRANSIT_CHANGE, pipTaskInfo).build();
+        final TransitionInfo.Change pipChange = info.getChanges().getFirst();
+        pipChange.setRotation(DISPLAY_ROTATION,
+                WindowConfiguration.ROTATION_UNDEFINED);
+        pipChange.setStartAbsBounds(PIP_BOUNDS);
+        pipChange.setEndAbsBounds(toSplit ? RIGHT_HALF_DISPLAY_BOUNDS : DISPLAY_BOUNDS);
+        pipChange.setLeash(mPipLeash);
+        pipChange.setLastParent(lastParent);
+        return info;
+    }
+
+    private static ActivityManager.RunningTaskInfo createPipTaskInfo(int taskId,
+            int windowingMode, PictureInPictureParams params) {
+        ActivityManager.RunningTaskInfo taskInfo = new ActivityManager.RunningTaskInfo();
+        taskInfo.taskId = taskId;
+        taskInfo.configuration.windowConfiguration.setWindowingMode(windowingMode);
+        taskInfo.token = mock(WindowContainerToken.class);
+        taskInfo.baseIntent = mock(Intent.class);
+        taskInfo.pictureInPictureParams = params;
+        return taskInfo;
+    }
+}