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文章出处:http://www.limodev.cn/blog
作者联系方式:李先静 <xianjimli@gmail.com>
Android GUI更新过程
相关组件
1.ViewRoot
在private void draw(boolean fullRedrawNeeded)中,会调用lockCanvas,从而获取一个Canvas对象,然后调用递归调用子窗口(View)的draw函数去绘制自己,最后调用unlockCanvasAndPost让Surface把自己更新到屏幕上。
canvas = surface.lockCanvas(dirty);mView.draw(canvas);surface.unlockCanvasAndPost(canvas);
2.android/view/Surface
它主要对一些native函数的包装。
private native Canvas lockCanvasNative(Rect dirty); public native void unlockCanvasAndPost(Canvas canvas);
3.android_view_Surface.cpp
这是native函数的实现。
Surface_lockCanvas它先锁住Surface,从而获取Surface相关的信息,如果格式、宽度、高度和像素缓冲区。然后创建一个bitmap,这个bitmap和共享一个像素缓冲区,这样View就能直接把自己绘制到Surface上了。
status_t err = surface->lock(&info, &dirtyRegion);bitmap.setPixels(info.bits);nativeCanvas->setBitmapDevice(bitmap);
Surface_unlockCanvasAndPost它断开SkCanvas与Surface之间的关系,然后调用Surface的unlockAndPost。
nativeCanvas->setBitmapDevice(SkBitmap());status_t err = surface->unlockAndPost();
4.surfaceflinger_client/Surface.cpp
Surface::lock调用dequeueBuffer获取一个可用的Buffer,dequeueBuffer会调用SharedBufferClient::dequeue等到backbuffer可用,然后锁住这个Buffer并填充相关信息。
status_t err = dequeueBuffer(&backBuffer);err = lockBuffer(backBuffer.get());
Surface::unlockAndPost先unlock Buffer,然后调queueBuffer显示Buffer。
status_t err = mLockedBuffer->unlock();err = queueBuffer(mLockedBuffer.get());
Surface::queueBuffer是比较有意思的,它设置更新的区域,然后通知服务端(SurfaceFlinger)。
mSharedBufferClient->setDirtyRegion(bufIdx, mDirtyRegion);err = mSharedBufferClient->queue(bufIdx);client->signalServer();
通过binder发送请求给服务:
virtual void signal() const { Parcel data, reply; data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor()); remote()->transact(BnSurfaceComposer::SIGNAL, data, &reply, IBinder::FLAG_ONEWAY); }
5.SurfaceFlinger
BnSurfaceComposer::onTransact case SIGNAL: { CHECK_INTERFACE(ISurfaceComposer, data, reply); signal(); } break;
这是SurfaceFlinger中处理SIGNAL的代码,它调用SurfaceFlinger::signal,再调用 SurfaceFlinger::signalEvent,最后调用MessageQueue::invalidate唤醒是 SurfaceFlinger的主循环。
在主循环中waitForEvent返回,再handleRepaint去合成个Layer/Surface。
bool SurfaceFlinger::threadLoop(){ waitForEvent(); handleRepaint(); postFramebuffer();}
SurfaceFlinger::handleRepaint会调用composeSurfaces把需要绘制各个Surface合并起来,绘制到FrameBuffer的BackBuffer上。
for (size_t i=0 ; i<count ; ++i) { const sp<LayerBase>& layer = layers[i]; const Region& visibleRegion(layer->visibleRegionScreen); if (!visibleRegion.isEmpty()) { /* broncho cy add */#ifdef USEOVERLAY mToppest[1] = mToppest[0]; mToppest[0] = layer->getIdentity();#endif /* broncho end */ const Region clip(dirty.intersect(visibleRegion)); if (!clip.isEmpty()) { layer->draw(clip); } } }
SurfaceFlinger::postFramebuffer最后把FrameBuffer的BackBuffer显示到屏幕上:
hw.flip(mInvalidRegion); -->eglSwapBuffers(dpy, surface);
FrameBuffer具体的显示过程,下次再写吧。