Android 13 PIP画中画模式系统流程

// ActivityTaskManagerService.java
    boolean enterPictureInPictureMode(@NonNull ActivityRecord r, PictureInPictureParams params) {
        // 如果 activity 已经处于画中画模式，则返回
        if (r.inPinnedWindowingMode()) {
            return true;
        }
        // Activity支持画中画，现在检查我们此时是否可以进入画中画，
        if (!r.checkEnterPictureInPictureState("enterPictureInPictureMode",
                false /* beforeStopping */)) {
            return false;
        }
        // 创建了一个 Runnable，在下方将会被调用
        final Runnable enterPipRunnable = () -> {
            synchronized (mGlobalLock) {
                if (r.getParent() == null) {
                    Slog.e(TAG, "Skip enterPictureInPictureMode, destroyed " + r);
                    return;
                }
                r.setPictureInPictureParams(params);
                // **--------重点关注-------------**
                mRootWindowContainer.moveActivityToPinnedRootTask(r,
                        null /* launchIntoPipHostActivity */, "enterPictureInPictureMode");
                final Task task = r.getTask();
                // Continue the pausing process after entering pip.
                if (task.getPausingActivity() == r) {
                    task.schedulePauseActivity(r, false /* userLeaving */,
                            false /* pauseImmediately */, "auto-pip");
                }
            }
        };
        if (r.isKeyguardLocked()) {
            // 如果键盘锁正在显示或被遮挡，则在进入画中画之前尝试关闭它
            // 如果设备当前已锁定（有锁的情况），这将提示用户进行身份验证（即弹出bouncer）。
            mActivityClientController.dismissKeyguard(r.token, new KeyguardDismissCallback() {
                @Override
                public void onDismissSucceeded() {
                    mH.post(enterPipRunnable);
                }
            }, null /* message */);
        } else {
            // 否则立即进入画中画
            enterPipRunnable.run();
        }
        return true;
    }

// RootWindowContainer.java
    void moveActivityToPinnedRootTask(@NonNull ActivityRecord r,
            @Nullable ActivityRecord launchIntoPipHostActivity, String reason) {
        mService.deferWindowLayout();
        final TaskDisplayArea taskDisplayArea = r.getDisplayArea();
        try {
            // 获取任务栈
            final Task task = r.getTask();
            // 现在创建一个转换控制器以收集当前关闭的任务栈。
            // 由于进入 PIP 的任务（触发器）尚未准备好，因此在此处进行创建。
            final TransitionController transitionController = task.mTransitionController;
            Transition newTransition = null;
            if (transitionController.isCollecting()) {
                transitionController.setReady(task, false /* ready */);
            } else if (transitionController.getTransitionPlayer() != null) {
                newTransition = transitionController.createTransition(TRANSIT_PIP);
            }
            final Task rootPinnedTask = taskDisplayArea.getRootPinnedTask();
            if (rootPinnedTask != null) {
                transitionController.collect(rootPinnedTask);
                // 新的ActivityRecord应该取代现有的PiP，因此旧的PiP消失而不是同时转到全屏，
                // 正如Task#diseasePip试图做的那样。
                removeRootTasksInWindowingModes(WINDOWING_MODE_PINNED);
            }
            // 设置过渡以确保我们不会立即尝试更新可见性，进入 PIP 的活动
            r.getDisplayContent().prepareAppTransition(TRANSIT_NONE);
            final TaskFragment organizedTf = r.getOrganizedTaskFragment();
            final boolean singleActivity = task.getNonFinishingActivityCount() == 1;
            final Task rootTask;
            if (singleActivity) {
                rootTask = task;
                // 对进入PIP的任务应用最近一次的动画牵引变换
                rootTask.maybeApplyLastRecentsAnimationTransaction();
            } else {
                // 在多个活动的情况下，我们将为其创建一个新任务，
                // 然后将PIP活动移动到任务中。
                // 注意，我们明确地延迟了正在发送的任务，并将这个新创建的任务标记为可见
                rootTask = new Task.Builder(mService)
                        .setActivityType(r.getActivityType())
                        .setOnTop(true)
                        .setActivityInfo(r.info)
                        .setParent(taskDisplayArea)
                        .setIntent(r.intent)
                        .setDeferTaskAppear(true)
                        .setHasBeenVisible(true)
                        .build();
                // 在原始任务和固定任务之间建立双向链接。
                r.setLastParentBeforePip(launchIntoPipHostActivity);
                // 进入 PIP 的任务可能是自由格式的，因此请保存最后一个非全屏边界。
                // 然后当这个新的 PIP 任务退出 PIP 时，它可以恢复到它以前的自由形式边界
                rootTask.setLastNonFullscreenBounds(task.mLastNonFullscreenBounds);
                rootTask.setBounds(task.getBounds());
                // 将最后一个最近的动画事务从原始任务移动到新任务
                if (task.mLastRecentsAnimationTransaction != null) {
                    rootTask.setLastRecentsAnimationTransaction(
                            task.mLastRecentsAnimationTransaction,
                            task.mLastRecentsAnimationOverlay);
                    task.clearLastRecentsAnimationTransaction(false /* forceRemoveOverlay */);
                }
                if (organizedTf != null && organizedTf.getNonFinishingActivityCount() == 1
                        && organizedTf.getTopNonFinishingActivity() == r) {
                    // PIP 的状态，是否已清除 PIP 的TaskFragment。
                    // 一旦有改变将在 ActivityTaskManagerService#onPictureInPictureStateChanged() 收到回调
                    organizedTf.mClearedTaskFragmentForPip = true;
                }
                // Activity reparent 到新建的 task
                r.reparent(rootTask, MAX_VALUE, reason);
                // 确保修复后新任务的约束与其当前边界同步。
                rootTask.maybeApplyLastRecentsAnimationTransaction();
                final ActivityRecord oldTopActivity = task.getTopMostActivity();
                if (oldTopActivity != null && oldTopActivity.isState(STOPPED)
                        && task.getDisplayContent().mAppTransition.containsTransitRequest(
                        TRANSIT_TO_BACK)) {
                    task.getDisplayContent().mClosingApps.add(oldTopActivity);
                    oldTopActivity.mRequestForceTransition = true;
                }
            }
            final int intermediateWindowingMode = rootTask.getWindowingMode();
            if (rootTask.getParent() != taskDisplayArea) {
                rootTask.reparent(taskDisplayArea, true /* onTop */);
            }
            if (newTransition != null) {
                transitionController.requestStartTransition(newTransition, rootTask,
                        null /* remoteTransition */, null /* displayChange */);
            }
            transitionController.collect(rootTask);
            r.setWindowingMode(intermediateWindowingMode);
            r.mWaitForEnteringPinnedMode = true;
            rootTask.forAllTaskFragments(tf -> {
                if (!tf.isOrganizedTaskFragment()) {
                    return;
                }
                tf.resetAdjacentTaskFragment();
                if (tf.getTopNonFinishingActivity() != null) {
                    tf.updateRequestedOverrideConfiguration(EMPTY);
                }
            });
            rootTask.setWindowingMode(WINDOWING_MODE_PINNED);
            if (r.getOptions() != null && r.getOptions().isLaunchIntoPip()) {
                mWindowManager.mTaskSnapshotController.recordTaskSnapshot(
                        task, false /* allowSnapshotHome */);
                rootTask.setBounds(r.getOptions().getLaunchBounds());
            }
            rootTask.setDeferTaskAppear(false);
            r.supportsEnterPipOnTaskSwitch = false;
            if (organizedTf != null && organizedTf.mClearedTaskFragmentForPip
                    && organizedTf.isTaskVisibleRequested()) {
                mService.mTaskFragmentOrganizerController.dispatchPendingInfoChangedEvent(
                        organizedTf);
            }
        } finally {
            mService.continueWindowLayout();
        }
         // 显示
        ensureActivitiesVisible(null, 0, false /* preserveWindows */);
        resumeFocusedTasksTopActivities();
        notifyActivityPipModeChanged(r.getTask(), r);
    }

// ActivityTaskManagerService.java
    @Override
    public void onPictureInPictureStateChanged(PictureInPictureUiState pipState) {
        enforceTaskPermission("onPictureInPictureStateChanged");
        final Task rootPinnedTask = mRootWindowContainer.getDefaultTaskDisplayArea()
                .getRootPinnedTask();
        if (rootPinnedTask != null && rootPinnedTask.getTopMostActivity() != null) {
            // 这里将会去提醒客户端状态发生改变；
            mWindowManager.mAtmService.mActivityClientController.onPictureInPictureStateChanged(
                    rootPinnedTask.getTopMostActivity(), pipState);
        }
    }

void onPictureInPictureStateChanged(@NonNull ActivityRecord r,
            PictureInPictureUiState pipState) {
        if (!r.inPinnedWindowingMode()) {
            throw new IllegalStateException("Activity is not in PIP mode");
        }
        try {
            final ClientTransaction transaction = ClientTransaction.obtain(
                    r.app.getThread(), r.token);
            transaction.addCallback(PipStateTransactionItem.obtain(pipState));
            mService.getLifecycleManager().scheduleTransaction(transaction);
        } catch (Exception e) {
            Slog.w(TAG, "Failed to send pip state transaction item: "
                    + r.intent.getComponent(), e);
        }
    }