recents/views/TaskStackAnimationHelper.java

/*
 * Copyright (C) 2015 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.systemui.recents.views;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.TimeInterpolator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.content.res.Configuration;
import android.content.res.Resources;
import android.util.Log;
import android.view.View;
import android.view.animation.Interpolator;
import android.view.animation.PathInterpolator;

import com.android.systemui.Interpolators;
import com.android.systemui.R;
import com.android.systemui.recents.Recents;
import com.android.systemui.recents.RecentsActivityLaunchState;
import com.android.systemui.recents.RecentsConfiguration;
import com.android.systemui.recents.misc.ReferenceCountedTrigger;
import com.android.systemui.recents.model.Task;
import com.android.systemui.recents.model.TaskStack;

import java.util.ArrayList;
import java.util.List;

/**
 * A helper class to create task view animations for {@link TaskView}s in a {@link TaskStackView},
 * but not the contents of the {@link TaskView}s.
 */
public class TaskStackAnimationHelper {

    /**
     * Callbacks from the helper to coordinate view-content animations with view animations.
     */
    public interface Callbacks {
        /**
         * Callback to prepare for the start animation for the launch target {@link TaskView}.
         */
        void onPrepareLaunchTargetForEnterAnimation();

        /**
         * Callback to start the animation for the launch target {@link TaskView}.
         */
        void onStartLaunchTargetEnterAnimation(TaskViewTransform transform, int duration,
                boolean screenPinningEnabled, ReferenceCountedTrigger postAnimationTrigger);

        /**
         * Callback to start the animation for the launch target {@link TaskView} when it is
         * launched from Recents.
         */
        void onStartLaunchTargetLaunchAnimation(int duration, boolean screenPinningRequested,
                ReferenceCountedTrigger postAnimationTrigger);

        /**
         * Callback to start the animation for the front {@link TaskView} if there is no launch
         * target.
         */
        void onStartFrontTaskEnterAnimation(boolean screenPinningEnabled);
    }

    private static final int DOUBLE_FRAME_OFFSET_MS = 33;
    private static final int FRAME_OFFSET_MS = 16;

    private static final int ENTER_EXIT_NUM_ANIMATING_TASKS = 5;

    private static final int ENTER_FROM_HOME_ALPHA_DURATION = 100;
    public static final int ENTER_FROM_HOME_TRANSLATION_DURATION = 300;
    private static final Interpolator ENTER_FROM_HOME_TRANSLATION_INTERPOLATOR =
            Interpolators.LINEAR_OUT_SLOW_IN;
    private static final Interpolator ENTER_FROM_HOME_ALPHA_INTERPOLATOR = Interpolators.LINEAR;

    public static final int EXIT_TO_HOME_TRANSLATION_DURATION = 200;
    private static final Interpolator EXIT_TO_HOME_TRANSLATION_INTERPOLATOR =
            new PathInterpolator(0.4f, 0, 0.6f, 1f);

    private static final int DISMISS_TASK_DURATION = 175;
    private static final int DISMISS_ALL_TASKS_DURATION = 200;
    private static final Interpolator DISMISS_ALL_TRANSLATION_INTERPOLATOR =
            new PathInterpolator(0.4f, 0, 1f, 1f);

    private static final Interpolator FOCUS_NEXT_TASK_INTERPOLATOR =
            new PathInterpolator(0.4f, 0, 0, 1f);
    private static final Interpolator FOCUS_IN_FRONT_NEXT_TASK_INTERPOLATOR =
            new PathInterpolator(0, 0, 0, 1f);
    private static final Interpolator FOCUS_BEHIND_NEXT_TASK_INTERPOLATOR =
            Interpolators.LINEAR_OUT_SLOW_IN;

    private static final Interpolator ENTER_WHILE_DOCKING_INTERPOLATOR =
            Interpolators.LINEAR_OUT_SLOW_IN;

    private TaskStackView mStackView;

    private TaskViewTransform mTmpTransform = new TaskViewTransform();
    private ArrayList<TaskViewTransform> mTmpCurrentTaskTransforms = new ArrayList<>();
    private ArrayList<TaskViewTransform> mTmpFinalTaskTransforms = new ArrayList<>();

    public TaskStackAnimationHelper(Context context, TaskStackView stackView) {
        mStackView = stackView;
    }

    /**
     * Prepares the stack views and puts them in their initial animation state while visible, before
     * the in-app enter animations start (after the window-transition completes).
     */
    public void prepareForEnterAnimation() {
        RecentsConfiguration config = Recents.getConfiguration();
        RecentsActivityLaunchState launchState = config.getLaunchState();
        Resources res = mStackView.getResources();
        Resources appResources = mStackView.getContext().getApplicationContext().getResources();

        TaskStackLayoutAlgorithm stackLayout = mStackView.getStackAlgorithm();
        TaskStackViewScroller stackScroller = mStackView.getScroller();
        TaskStack stack = mStackView.getStack();
        Task launchTargetTask = stack.getLaunchTarget();

        // Break early if there are no tasks
        if (stack.getTaskCount() == 0) {
            return;
        }

        int offscreenYOffset = stackLayout.mStackRect.height();
        int taskViewAffiliateGroupEnterOffset = res.getDimensionPixelSize(
                R.dimen.recents_task_stack_animation_affiliate_enter_offset);
        int launchedWhileDockingOffset = res.getDimensionPixelSize(
                R.dimen.recents_task_stack_animation_launched_while_docking_offset);
        boolean isLandscape = appResources.getConfiguration().orientation
                == Configuration.ORIENTATION_LANDSCAPE;

        // Prepare each of the task views for their enter animation from front to back
        List<TaskView> taskViews = mStackView.getTaskViews();
        for (int i = taskViews.size() - 1; i >= 0; i--) {
            TaskView tv = taskViews.get(i);
            Task task = tv.getTask();
            boolean currentTaskOccludesLaunchTarget = launchTargetTask != null &&
                    launchTargetTask.group != null &&
                    launchTargetTask.group.isTaskAboveTask(task, launchTargetTask);
            boolean hideTask = launchTargetTask != null &&
                    launchTargetTask.isFreeformTask() &&
                    task.isFreeformTask();

            // Get the current transform for the task, which will be used to position it offscreen
            stackLayout.getStackTransform(task, stackScroller.getStackScroll(), mTmpTransform,
                    null);

            if (hideTask) {
                tv.setVisibility(View.INVISIBLE);
            } else if (launchState.launchedFromApp && !launchState.launchedViaDockGesture) {
                if (task.isLaunchTarget) {
                    tv.onPrepareLaunchTargetForEnterAnimation();
                } else if (currentTaskOccludesLaunchTarget) {
                    // Move the task view slightly lower so we can animate it in
                    mTmpTransform.rect.offset(0, taskViewAffiliateGroupEnterOffset);
                    mTmpTransform.alpha = 0f;
                    mStackView.updateTaskViewToTransform(tv, mTmpTransform,
                            AnimationProps.IMMEDIATE);
                    tv.setClipViewInStack(false);
                }
            } else if (launchState.launchedFromHome) {
                // Move the task view off screen (below) so we can animate it in
                mTmpTransform.rect.offset(0, offscreenYOffset);
                mTmpTransform.alpha = 0f;
                mStackView.updateTaskViewToTransform(tv, mTmpTransform, AnimationProps.IMMEDIATE);
            } else if (launchState.launchedViaDockGesture) {
                int offset = isLandscape
                        ? launchedWhileDockingOffset
                        : (int) (offscreenYOffset * 0.9f);
                mTmpTransform.rect.offset(0, offset);
                mTmpTransform.alpha = 0f;
                mStackView.updateTaskViewToTransform(tv, mTmpTransform, AnimationProps.IMMEDIATE);
            }
        }
    }

    /**
     * Starts the in-app enter animation, which animates the {@link TaskView}s to their final places
     * depending on how Recents was triggered.
     */
    public void startEnterAnimation(final ReferenceCountedTrigger postAnimationTrigger) {
        RecentsConfiguration config = Recents.getConfiguration();
        RecentsActivityLaunchState launchState = config.getLaunchState();
        Resources res = mStackView.getResources();
        Resources appRes = mStackView.getContext().getApplicationContext().getResources();

        TaskStackLayoutAlgorithm stackLayout = mStackView.getStackAlgorithm();
        TaskStackViewScroller stackScroller = mStackView.getScroller();
        TaskStack stack = mStackView.getStack();
        Task launchTargetTask = stack.getLaunchTarget();

        // Break early if there are no tasks
        if (stack.getTaskCount() == 0) {
            return;
        }

        int taskViewEnterFromAppDuration = res.getInteger(
                R.integer.recents_task_enter_from_app_duration);
        int taskViewEnterFromAffiliatedAppDuration = res.getInteger(
                R.integer.recents_task_enter_from_affiliated_app_duration);
        int dockGestureAnimDuration = appRes.getInteger(
                R.integer.long_press_dock_anim_duration);

        // Create enter animations for each of the views from front to back
        List<TaskView> taskViews = mStackView.getTaskViews();
        int taskViewCount = taskViews.size();
        for (int i = taskViewCount - 1; i >= 0; i--) {
            int taskIndexFromFront = taskViewCount - i - 1;
            int taskIndexFromBack = i;
            final TaskView tv = taskViews.get(i);
            Task task = tv.getTask();
            boolean currentTaskOccludesLaunchTarget = launchTargetTask != null &&
                    launchTargetTask.group != null &&
                    launchTargetTask.group.isTaskAboveTask(task, launchTargetTask);

            // Get the current transform for the task, which will be updated to the final transform
            // to animate to depending on how recents was invoked
            stackLayout.getStackTransform(task, stackScroller.getStackScroll(), mTmpTransform,
                    null);

            if (launchState.launchedFromApp && !launchState.launchedViaDockGesture) {
                if (task.isLaunchTarget) {
                    tv.onStartLaunchTargetEnterAnimation(mTmpTransform,
                            taskViewEnterFromAppDuration, mStackView.mScreenPinningEnabled,
                            postAnimationTrigger);
                } else {
                    // Animate the task up if it was occluding the launch target
                    if (currentTaskOccludesLaunchTarget) {
                        AnimationProps taskAnimation = new AnimationProps(
                                taskViewEnterFromAffiliatedAppDuration, Interpolators.ALPHA_IN,
                                new AnimatorListenerAdapter() {
                                    @Override
                                    public void onAnimationEnd(Animator animation) {
                                        postAnimationTrigger.decrement();
                                        tv.setClipViewInStack(true);
                                    }
                                });
                        postAnimationTrigger.increment();
                        mStackView.updateTaskViewToTransform(tv, mTmpTransform, taskAnimation);
                    }
                }

            } else if (launchState.launchedFromHome) {
                // Animate the tasks up, but offset the animations to be relative to the front-most
                // task animation
                AnimationProps taskAnimation = new AnimationProps()
                        .setInitialPlayTime(AnimationProps.BOUNDS,
                                Math.min(ENTER_EXIT_NUM_ANIMATING_TASKS, taskIndexFromFront) *
                                        DOUBLE_FRAME_OFFSET_MS)
                        .setStartDelay(AnimationProps.ALPHA,
                                Math.min(ENTER_EXIT_NUM_ANIMATING_TASKS, taskIndexFromFront) *
                                        FRAME_OFFSET_MS)
                        .setDuration(AnimationProps.BOUNDS, ENTER_FROM_HOME_TRANSLATION_DURATION)
                        .setDuration(AnimationProps.ALPHA, ENTER_FROM_HOME_ALPHA_DURATION)
                        .setInterpolator(AnimationProps.BOUNDS,
                                ENTER_FROM_HOME_TRANSLATION_INTERPOLATOR)
                        .setInterpolator(AnimationProps.ALPHA, ENTER_FROM_HOME_ALPHA_INTERPOLATOR)
                        .setListener(postAnimationTrigger.decrementOnAnimationEnd());
                postAnimationTrigger.increment();
                mStackView.updateTaskViewToTransform(tv, mTmpTransform, taskAnimation);
                if (i == taskViewCount - 1) {
                    tv.onStartFrontTaskEnterAnimation(mStackView.mScreenPinningEnabled);
                }
            } else if (launchState.launchedViaDockGesture) {
                // Animate the tasks up - add some delay to match the divider animation
                AnimationProps taskAnimation = new AnimationProps()
                        .setDuration(AnimationProps.BOUNDS, dockGestureAnimDuration +
                                (taskIndexFromBack * DOUBLE_FRAME_OFFSET_MS))
                        .setInterpolator(AnimationProps.BOUNDS,
                                ENTER_WHILE_DOCKING_INTERPOLATOR)
                        .setStartDelay(AnimationProps.BOUNDS, 48)
                        .setListener(postAnimationTrigger.decrementOnAnimationEnd());
                postAnimationTrigger.increment();
                mStackView.updateTaskViewToTransform(tv, mTmpTransform, taskAnimation);
            }
        }
    }

    /**
     * Starts an in-app animation to hide all the task views so that we can transition back home.
     */
    public void startExitToHomeAnimation(boolean animated,
            ReferenceCountedTrigger postAnimationTrigger) {
        TaskStackLayoutAlgorithm stackLayout = mStackView.getStackAlgorithm();
        TaskStack stack = mStackView.getStack();

        // Break early if there are no tasks
        if (stack.getTaskCount() == 0) {
            return;
        }

        int offscreenYOffset = stackLayout.mStackRect.height();

        // Create the animations for each of the tasks
        List<TaskView> taskViews = mStackView.getTaskViews();
        int taskViewCount = taskViews.size();
        for (int i = 0; i < taskViewCount; i++) {
            int taskIndexFromFront = taskViewCount - i - 1;
            TaskView tv = taskViews.get(i);
            Task task = tv.getTask();

            if (mStackView.isIgnoredTask(task)) {
                continue;
            }

            // Animate the tasks down
            AnimationProps taskAnimation;
            if (animated) {
                int delay = Math.min(ENTER_EXIT_NUM_ANIMATING_TASKS , taskIndexFromFront) *
                        DOUBLE_FRAME_OFFSET_MS;
                taskAnimation = new AnimationProps()
                        .setStartDelay(AnimationProps.BOUNDS, delay)
                        .setDuration(AnimationProps.BOUNDS, EXIT_TO_HOME_TRANSLATION_DURATION)
                        .setInterpolator(AnimationProps.BOUNDS,
                                EXIT_TO_HOME_TRANSLATION_INTERPOLATOR)
                        .setListener(postAnimationTrigger.decrementOnAnimationEnd());
                postAnimationTrigger.increment();
            } else {
                taskAnimation = AnimationProps.IMMEDIATE;
            }

            mTmpTransform.fillIn(tv);
            mTmpTransform.rect.offset(0, offscreenYOffset);
            mStackView.updateTaskViewToTransform(tv, mTmpTransform, taskAnimation);
        }
    }

    /**
     * Starts the animation for the launching task view, hiding any tasks that might occlude the
     * window transition for the launching task.
     */
    public void startLaunchTaskAnimation(TaskView launchingTaskView, boolean screenPinningRequested,
            final ReferenceCountedTrigger postAnimationTrigger) {
        Resources res = mStackView.getResources();

        int taskViewExitToAppDuration = res.getInteger(
                R.integer.recents_task_exit_to_app_duration);
        int taskViewAffiliateGroupEnterOffset = res.getDimensionPixelSize(
                R.dimen.recents_task_stack_animation_affiliate_enter_offset);

        Task launchingTask = launchingTaskView.getTask();
        List<TaskView> taskViews = mStackView.getTaskViews();
        int taskViewCount = taskViews.size();
        for (int i = 0; i < taskViewCount; i++) {
            TaskView tv = taskViews.get(i);
            Task task = tv.getTask();
            boolean currentTaskOccludesLaunchTarget = launchingTask != null &&
                    launchingTask.group != null &&
                    launchingTask.group.isTaskAboveTask(task, launchingTask);

            if (tv == launchingTaskView) {
                tv.setClipViewInStack(false);
                postAnimationTrigger.addLastDecrementRunnable(new Runnable() {
                    @Override
                    public void run() {
                        tv.setClipViewInStack(true);
                    }
                });
                tv.onStartLaunchTargetLaunchAnimation(taskViewExitToAppDuration,
                        screenPinningRequested, postAnimationTrigger);
            } else if (currentTaskOccludesLaunchTarget) {
                // Animate this task out of view
                AnimationProps taskAnimation = new AnimationProps(
                        taskViewExitToAppDuration, Interpolators.ALPHA_OUT,
                        postAnimationTrigger.decrementOnAnimationEnd());
                postAnimationTrigger.increment();

                mTmpTransform.fillIn(tv);
                mTmpTransform.alpha = 0f;
                mTmpTransform.rect.offset(0, taskViewAffiliateGroupEnterOffset);
                mStackView.updateTaskViewToTransform(tv, mTmpTransform, taskAnimation);
            }
        }
    }

    /**
     * Starts the delete animation for the specified {@link TaskView}.
     */
    public void startDeleteTaskAnimation(final TaskView deleteTaskView,
            final ReferenceCountedTrigger postAnimationTrigger) {
        TaskStackViewTouchHandler touchHandler = mStackView.getTouchHandler();
        touchHandler.onBeginManualDrag(deleteTaskView);

        postAnimationTrigger.increment();
        postAnimationTrigger.addLastDecrementRunnable(() -> {
            touchHandler.onChildDismissed(deleteTaskView);
        });

        final float dismissSize = touchHandler.getScaledDismissSize();
        ValueAnimator animator = ValueAnimator.ofFloat(0f, 1f);
        animator.setDuration(400);
        animator.addUpdateListener((animation) -> {
            float progress = (Float) animation.getAnimatedValue();
            deleteTaskView.setTranslationX(progress * dismissSize);
            touchHandler.updateSwipeProgress(deleteTaskView, true, progress);
        });
        animator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                postAnimationTrigger.decrement();
            }
        });
        animator.start();
    }

    /**
     * Starts the delete animation for all the {@link TaskView}s.
     */
    public void startDeleteAllTasksAnimation(final List<TaskView> taskViews,
                                             final ReferenceCountedTrigger postAnimationTrigger) {
        TaskStackLayoutAlgorithm stackLayout = mStackView.getStackAlgorithm();

        int offscreenXOffset = mStackView.getMeasuredWidth() - stackLayout.mTaskRect.left;

        int taskViewCount = taskViews.size();
        for (int i = taskViewCount - 1; i >= 0; i--) {
            TaskView tv = taskViews.get(i);
            int taskIndexFromFront = taskViewCount - i - 1;
            int startDelay = taskIndexFromFront * DOUBLE_FRAME_OFFSET_MS;

            // Disabling clipping with the stack while the view is animating away
            tv.setClipViewInStack(false);

            // Compose the new animation and transform and star the animation
            AnimationProps taskAnimation = new AnimationProps(startDelay,
                    DISMISS_ALL_TASKS_DURATION, DISMISS_ALL_TRANSLATION_INTERPOLATOR,
                    new AnimatorListenerAdapter() {
                @Override
                public void onAnimationEnd(Animator animation) {
                    postAnimationTrigger.decrement();

                    // Re-enable clipping with the stack (we will reuse this view)
                    tv.setClipViewInStack(true);
                }
            });
            postAnimationTrigger.increment();

            mTmpTransform.fillIn(tv);
            mTmpTransform.rect.offset(offscreenXOffset, 0);
            mStackView.updateTaskViewToTransform(tv, mTmpTransform, taskAnimation);
        }
    }

    /**
     * Starts the animation to focus the next {@link TaskView} when paging through recents.
     *
     * @return whether or not this will trigger a scroll in the stack
     */
    public boolean startScrollToFocusedTaskAnimation(Task newFocusedTask,
            boolean requestViewFocus) {
        TaskStackLayoutAlgorithm stackLayout = mStackView.getStackAlgorithm();
        TaskStackViewScroller stackScroller = mStackView.getScroller();
        TaskStack stack = mStackView.getStack();

        final float curScroll = stackScroller.getStackScroll();
        final float newScroll = stackScroller.getBoundedStackScroll(
                stackLayout.getStackScrollForTask(newFocusedTask));
        boolean willScrollToFront = newScroll > curScroll;
        boolean willScroll = Float.compare(newScroll, curScroll) != 0;

        // Get the current set of task transforms
        int taskViewCount = mStackView.getTaskViews().size();
        ArrayList<Task> stackTasks = stack.getStackTasks();
        mStackView.getCurrentTaskTransforms(stackTasks, mTmpCurrentTaskTransforms);

        // Pick up the newly visible views after the scroll
        mStackView.bindVisibleTaskViews(newScroll);

        // Update the internal state
        stackLayout.setFocusState(TaskStackLayoutAlgorithm.STATE_FOCUSED);
        stackScroller.setStackScroll(newScroll, null /* animation */);
        mStackView.cancelDeferredTaskViewLayoutAnimation();

        // Get the final set of task transforms
        mStackView.getLayoutTaskTransforms(newScroll, stackLayout.getFocusState(), stackTasks,
                true /* ignoreTaskOverrides */, mTmpFinalTaskTransforms);

        // Focus the task view
        TaskView newFocusedTaskView = mStackView.getChildViewForTask(newFocusedTask);
        if (newFocusedTaskView == null) {
            // Log the error if we have no task view, and skip the animation
            Log.e("TaskStackAnimationHelper", "b/27389156 null-task-view prebind:" + taskViewCount +
                    " postbind:" + mStackView.getTaskViews().size() + " prescroll:" + curScroll +
                    " postscroll: " + newScroll);
            return false;
        }
        newFocusedTaskView.setFocusedState(true, requestViewFocus);

        // Setup the end listener to return all the hidden views to the view pool after the
        // focus animation
        ReferenceCountedTrigger postAnimTrigger = new ReferenceCountedTrigger();
        postAnimTrigger.addLastDecrementRunnable(new Runnable() {
            @Override
            public void run() {
                mStackView.bindVisibleTaskViews(newScroll);
            }
        });

        List<TaskView> taskViews = mStackView.getTaskViews();
        taskViewCount = taskViews.size();
        int newFocusTaskViewIndex = taskViews.indexOf(newFocusedTaskView);
        for (int i = 0; i < taskViewCount; i++) {
            TaskView tv = taskViews.get(i);
            Task task = tv.getTask();

            if (mStackView.isIgnoredTask(task)) {
                continue;
            }

            int taskIndex = stackTasks.indexOf(task);
            TaskViewTransform fromTransform = mTmpCurrentTaskTransforms.get(taskIndex);
            TaskViewTransform toTransform = mTmpFinalTaskTransforms.get(taskIndex);

            // Update the task to the initial state (for the newly picked up tasks)
            mStackView.updateTaskViewToTransform(tv, fromTransform, AnimationProps.IMMEDIATE);

            int duration;
            Interpolator interpolator;
            if (willScrollToFront) {
                duration = calculateStaggeredAnimDuration(i);
                interpolator = FOCUS_BEHIND_NEXT_TASK_INTERPOLATOR;
            } else {
                if (i < newFocusTaskViewIndex) {
                    duration = 150 + ((newFocusTaskViewIndex - i - 1) * 50);
                    interpolator = FOCUS_BEHIND_NEXT_TASK_INTERPOLATOR;
                } else if (i > newFocusTaskViewIndex) {
                    duration = Math.max(100, 150 - ((i - newFocusTaskViewIndex - 1) * 50));
                    interpolator = FOCUS_IN_FRONT_NEXT_TASK_INTERPOLATOR;
                } else {
                    duration = 200;
                    interpolator = FOCUS_NEXT_TASK_INTERPOLATOR;
                }
            }

            AnimationProps anim = new AnimationProps()
                    .setDuration(AnimationProps.BOUNDS, duration)
                    .setInterpolator(AnimationProps.BOUNDS, interpolator)
                    .setListener(postAnimTrigger.decrementOnAnimationEnd());
            postAnimTrigger.increment();
            mStackView.updateTaskViewToTransform(tv, toTransform, anim);
        }
        return willScroll;
    }

    /**
     * Starts the animation to go to the initial stack layout with a task focused.  In addition, the
     * previous task will be animated in after the scroll completes.
     */
    public void startNewStackScrollAnimation(TaskStack newStack,
            ReferenceCountedTrigger animationTrigger) {
        TaskStackLayoutAlgorithm stackLayout = mStackView.getStackAlgorithm();
        TaskStackViewScroller stackScroller = mStackView.getScroller();

        // Get the current set of task transforms
        ArrayList<Task> stackTasks = newStack.getStackTasks();
        mStackView.getCurrentTaskTransforms(stackTasks, mTmpCurrentTaskTransforms);

        // Update the stack
        mStackView.setTasks(newStack, false /* allowNotifyStackChanges */);
        mStackView.updateLayoutAlgorithm(false /* boundScroll */);

        // Pick up the newly visible views after the scroll
        final float newScroll = stackLayout.mInitialScrollP;
        mStackView.bindVisibleTaskViews(newScroll);

        // Update the internal state
        stackLayout.setFocusState(TaskStackLayoutAlgorithm.STATE_UNFOCUSED);
        stackLayout.setTaskOverridesForInitialState(newStack, true /* ignoreScrollToFront */);
        stackScroller.setStackScroll(newScroll);
        mStackView.cancelDeferredTaskViewLayoutAnimation();

        // Get the final set of task transforms
        mStackView.getLayoutTaskTransforms(newScroll, stackLayout.getFocusState(), stackTasks,
                false /* ignoreTaskOverrides */, mTmpFinalTaskTransforms);

        // Hide the front most task view until the scroll is complete
        Task frontMostTask = newStack.getStackFrontMostTask(false /* includeFreeform */);
        final TaskView frontMostTaskView = mStackView.getChildViewForTask(frontMostTask);
        final TaskViewTransform frontMostTransform = mTmpFinalTaskTransforms.get(
                stackTasks.indexOf(frontMostTask));
        if (frontMostTaskView != null) {
            mStackView.updateTaskViewToTransform(frontMostTaskView,
                    stackLayout.getFrontOfStackTransform(), AnimationProps.IMMEDIATE);
        }

        // Setup the end listener to return all the hidden views to the view pool after the
        // focus animation
        animationTrigger.addLastDecrementRunnable(new Runnable() {
            @Override
            public void run() {
                mStackView.bindVisibleTaskViews(newScroll);

                // Now, animate in the front-most task
                if (frontMostTaskView != null) {
                    mStackView.updateTaskViewToTransform(frontMostTaskView, frontMostTransform,
                            new AnimationProps(75, 250, FOCUS_BEHIND_NEXT_TASK_INTERPOLATOR));
                }
            }
        });

        List<TaskView> taskViews = mStackView.getTaskViews();
        int taskViewCount = taskViews.size();
        for (int i = 0; i < taskViewCount; i++) {
            TaskView tv = taskViews.get(i);
            Task task = tv.getTask();

            if (mStackView.isIgnoredTask(task)) {
                continue;
            }
            if (task == frontMostTask && frontMostTaskView != null) {
                continue;
            }

            int taskIndex = stackTasks.indexOf(task);
            TaskViewTransform fromTransform = mTmpCurrentTaskTransforms.get(taskIndex);
            TaskViewTransform toTransform = mTmpFinalTaskTransforms.get(taskIndex);

            // Update the task to the initial state (for the newly picked up tasks)
            mStackView.updateTaskViewToTransform(tv, fromTransform, AnimationProps.IMMEDIATE);

            int duration = calculateStaggeredAnimDuration(i);
            Interpolator interpolator = FOCUS_BEHIND_NEXT_TASK_INTERPOLATOR;

            AnimationProps anim = new AnimationProps()
                    .setDuration(AnimationProps.BOUNDS, duration)
                    .setInterpolator(AnimationProps.BOUNDS, interpolator)
                    .setListener(animationTrigger.decrementOnAnimationEnd());
            animationTrigger.increment();
            mStackView.updateTaskViewToTransform(tv, toTransform, anim);
        }
    }

    /**
     * Caclulates a staggered duration for {@link #startScrollToFocusedTaskAnimation} and
     * {@link #startNewStackScrollAnimation}.
     */
    private int calculateStaggeredAnimDuration(int i) {
        return Math.max(100, 100 + ((i - 1) * 50));
    }
}