class Window {
    getSurface() -> Surface
    setWindowCallback(callback: WindowCallback)
    //Posts a callback to run on the next frame.
    //The callback runs once then is automatically removed.
    postVsyncCallback(callback: VsyncCallback， type: VsyncCallbackType)
}

protocol WindowCallback {
    onAttached()
    onDetached()
    onFocusChanged(hasFocus: Bool)
    onInputEvent(event: InputEvent)
}

protocol VsyncCallback {
    onVsync(frameTimeNanos: long)
}

enum VsyncCallbackType {
    // Called before drawing
    case animation
    case drawing
}

class Surface {
    isValid() -> Bool
    setCallback(callback: SurfaceCallback)
}

protocol SurfaceCallback {
    // Start up whatever rendering code you desire.
    onSurfaceCreated()
    //This method is always called at least once, after surfaceCreated.
    onSurfaceChanged(format: PixelFormat, width: Int32, height: Int32)
    //After returning from this call, you should no longer try to access this surface.
    onSurfaceDestroyed()
    //You should initiate the redraw, and return, later invoking drawingFinished when
    //your redraw is complete.
    onRedrawRequest(callback: DrawingFinishCallback)
}

protocol DrawingFinishCallback {
    onDrawingFinished()
}

sequenceDiagram

box MindUI
participant v as Context
participant vc as VsyncCallback
participant wc as WindowCallback
participant sc as SurfaceCallback
end

participant s as Surface
participant w as Window
participant wm as WindowManager
participant c as Choreographer

v ->>+ wm: 1. addWindow(name, attrs)
wm ->> w: new
wm -->>- v: window

wc ->> w: 2. setWindowCallback(WindowCallback)
w ->> wc: onInputEvent

vc ->> w: 3. postVsyncCallback(VsyncCallback)
c ->> vc: onVsync()
vc ->> v: animating / drawing

sc ->> s: 4. setSurfaceCallback(SurfaceCallback)
c ->> w: performTraversal
w ->> wc: onAttached
w ->> wm: relayoutWindow
wm -->> w: Surface

alt surface created
w ->> sc: onSurfaceCreated
w ->> sc: onSurfaceChanged(format, width, height)
else surface destroyed
w ->> sc: onSurfaceDestroy
end

s ->> sc: onRedrawRequest(DrawingFinishCallback)
sc ->> w: onDrawingFinished
w ->> wm: reportDrawFinished

1. 调用 addWindow() 创建一个窗口。
2. 调用 setWindowCallback() 向 Window 设置 WindowCallback，接收 InputEvent、窗口焦点切换等回调。
3. 调用 postVsyncCalback() 申请一次 VSYNC。一次 VSYNC 中 animation 类型的回调早于 drawing 类型。
4. 调用 setSurfaceCallback() 向 Suface 设置 SurfaceCallback。它可以接收 Surface 变化。在 Window 的 performTraversal() 流程中：
   1. 调用 onAttached()，表示 Window 已经添加到 WindowManager。
   2. 调用 relayoutWindow()，向 WindowManagerService 申请/销毁/更新 Surface。
   3. Surface 创建时调用 onSurfaceCreated() 和 onSurfaceChanged()。
   4. Surface 销毁时调用 onSurfaceDestroyed()，之后无法访问 Surface。
   5. 调用 onRedrawRequest() 请求一次绘制，并设置 DrawingFinishCallback。
   6. 绘制完成之后回调 onDrawingFinished()。
   7. 调用 reportDrawFinished() 通知 WindowManagerService 绘制一帧完成。