Android GUI update process

Indicate the source and author's contact information during reprinting.
Article Source: http://www.limodev.cn/blog

Author contact: Li xianjing <xianjimli@gmail.com>

 

Android GUI update process

Related Components

1. viewroot
In private void draw (Boolean
In fullredrawneeded), lockcanvas is called to obtain a canvas object, and the draw function of the sub-window (View) is called recursively.
Draw yourself, and finally call unlockcanvasandpost to let the surface update itself to the screen.

canvas = surface.lockCanvas(dirty);mView.draw(canvas);surface.unlockCanvasAndPost(canvas);

2. Android/View/Surface
It mainly encapsulates some native functions.

    private native Canvas lockCanvasNative(Rect dirty);    public native   void unlockCanvasAndPost(Canvas canvas);

3. android_view_surface.cpp
This is the implementation of native functions.
Surface_lockcanvas First locks the surface to obtain information about the surface, such as the format, width, height, and Pixel Buffer. Then create a bitmap, which shares a pixel buffer, so that the view can directly draw itself to the surface.

status_t err = surface->lock(&info, &dirtyRegion);bitmap.setPixels(info.bits);nativeCanvas->setBitmapDevice(bitmap);

Surface_unlockcanvasandpost it disconnects the relationship between the skcanvas and the surface, and then calls the surface's unlockandpost.

nativeCanvas->setBitmapDevice(SkBitmap());status_t err = surface->unlockAndPost();

4. surfaceflinger_client/surface. cpp
Surface: Lock call dequeuebuffer to obtain an available buffer. dequeuebuffer calls sharedbufferclient: dequeue to wait until the backbuffer is available, lock the buffer and fill in relevant information.

status_t err = dequeueBuffer(&backBuffer);err = lockBuffer(backBuffer.get());

Surface: unlockandpost first unlock buffer, then call queuebuffer to display buffer.

status_t err = mLockedBuffer->unlock();err = queueBuffer(mLockedBuffer.get());

Surface: queuebuffer is interesting. It sets the updated region and notifies the server (surfaceflinger ).

mSharedBufferClient->setDirtyRegion(bufIdx, mDirtyRegion);err = mSharedBufferClient->queue(bufIdx);client->signalServer();

Send a request to the service using the binder:

    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;

This is the code for processing signal in surfaceflinger. It calls surfaceflinger: signal and then calls
Surfaceflinger: signalevent, and finally call messagequeue: invalidate to wake up
The main loop of surfaceflinger.

In the main loop, waitforevent is returned, and handlerepaint is used to synthesize a layer/surface.

bool SurfaceFlinger::threadLoop(){    waitForEvent();       handleRepaint();       postFramebuffer();}

Surfaceflinger: handlerepaint will call composesurfaces to merge the surfaces to be drawn and draw them to the backbuffer of framebuffer.

    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 finally displays the buffer of framebuffer on the screen:

hw.flip(mInvalidRegion); -->eglSwapBuffers(dpy, surface);

The specific display process of framebuffer. Write it again next time.