Having known that BufferQueue exposes the APIs for consuming surface frame while implementing BnGraphicBufferProducer, we continue our attempt to demystify surface compositions and rendering with an examination of a few more classes with respect to surface composing.
- SurfaceFlingerConsumer and GLConsumer class
Defined in framework/native/services/surfaceflinger/SurfaceFlingerConsumer.h, and framework/native/include/gui/GLConsumer.h, SurfaceFlingerConsumer and GLConsumer are the core classes to fetch the current buffer from BufferQueue to bind to a surface layer specific GL texture. GLConsumer uses GLES functions to conduct the operation while SurfaceFlingerConsumer is a wrapper around it to safeguard the operation. The main APIs in SurfaceFlingerConsumer are updateTexImage() and bindTextureImage().
Note that a surface frame will be drawn to the display frame buffer as a GL texture and GLConsumer inherits from ConsumerBase.
- Layer Class
It has been known that when a SurfaceComposerClient::createSurface is invoked, Client in SurfaceFlinger posts a MessageCreateLayer to SurfaceFlinger which in turn calls SurfaceFlinger::createLayer() create a Layer instance to service the remote Surface instance.
Applying a lazy initialization, Layer delays until first reference to instantiate a BufferQueue object and SurfaceFlingerConsumer corresponding to the remote Surface object; meanwhile Layer links the BufferQueue object to SurfaceFlingerConsumer object and register itself as SurfaceFlingerConsumer::FrameAvailableListener listener among other procedures.
When Surface::queueBuffer() is invoked, BufferQueue::queueBuffer() and Layer::onFrameAvailable() call ensue ,as we elaborated in post SurfaceFlinger(III).
Subsequently , the Layer::draw() and Layer::onDraw() will be called to run SurfaceFlingerConsumer::bindTextureImage() and Layer::drawWithOpenGL() to FramebufferSurface current frame buffer.
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