Display Switch

Switch and Display between Containers

Background

SurfaceFlinger

• SurfaceFlinger inside has a series of layers,which correspond to the windows of applications
• SurfaceFlinger overlaps the windows according to the Z value of layers,calculates the blanking and display the synthetic frames
• SurfaceFlinger's Z value is set by WindowManagerService

WindowManagerService

• WMS inside has a series of WindowStates,which correspond to the windows of applications
• WMS decides the position of windows according to the startup sequence，activated state and system interface state
• WMS set the Z value of corresponding layer in SurfaceFlinger according to the windows's position

Solution

1. Add ContainerThread for WMS

• ContainerThread code consists in frameworks/base/services/java/com/android/server/wm/WindowManagerService.java,which is a class of thread
• ContainerThread call Container.registerContainer() to register current container when created
• ContainerThread call Container.waitingForNewPosition() to wait for the change of current container's position while running
• When the position is changed,ContainerThread will send a message to ContainerHandler

2. Add ContainerHandler for WMS

• ContainerHandler code consists in frameworks/base/services/java/com/android/server/wm/WindowManagerService.java,which is a class of thread

• When ContainerHandler receives CONTAINER_POSITION_CHANGED message:

    1. Set WMS's member variable-mContainerAdjustment as the current container's position * 1,000,000
    2. call WMS.scheduleAnimationLocked() to refresh Z value of windows
  

3 .Modify WindowManagerService

• mContainerAdjustment,WMS's member variable,is to save adjusted Z value of current container
• WMS set Z value of SurfaceFlinger;it will add mContainerAdjustment on the normal Z value

4. Modify WindowStateAnimator

• mLastContainerAdjustment,WindowStateAnimator's member variable,is to save last value of WMS.mContainerAdjustment
• Code consists in function createSurfaceLocked() and prepareSurfaceLocked()of WindowStateAnimator class to set Z value

• function createSurfaceLocked() is to create a surface for windows,when calling:

    1. Get WMS.mContainerAdjustment's value
    2. Save it by mLastContainerAdjustment
    3. Set windows's Z value as mAnimLayer + WMS.mContainerAdjustment
  

• function prepareSurfaceLocked() is to refresh windows's state,when calling:

    1. Get WMS.mContainerAdjustment's value
    2. Judge the value,if it's same as mLastContainerAdjustment's value
    3. If the same,refresh Z value as mAnimLayer + WMS.mContainerAdjustment
    4. Update mLastContainerAdjustment's value as WMS.mContainerAdjustment
  

  Modified files

• /frameworks/base/services/java/com/android/server/wm/WindowManagerService.java
• /frameworks/base/services/java/com/android/server/wm/WindowStateAnimator.java
• Don't need to modify relevant Android.mk

Reference Graph and explanation

Linux Kernel中的Container device drive保存了当前各个container的前后顺序，当不同container进行切换时，如何在屏幕上及时准确地显示出来呢？

我们首先在WMS(WindowManagerService)借助ContainerThread，创建线程时注册当前的Container；线程运行时监测当前Container的位置是否发生改变，当前Container的位置发生变化时，ContainerThread会发送一个message给ContainerHandler；

ContainerHandler收到message后，将当前container的位置乘以1,000,000，新值赋给WMS的成员变量mContainerAdjustment；并刷新窗口的Z值；WMS设置SurfaceFlinger中的Z值时会在正常的Z值之上加上mContainerAdjustment；

通过WindowStateAnimator的成员变量mLastContainerAdjustment和WMS.mContainerAdjustment比较，并更新值。