surfaceflinger: update BufferLayerConsumer comments

/*

 * BufferLayerConsumer consumes buffers of graphics data from a BufferQueue,

 * and makes them available to OpenGL as a texture.

 * and makes them available to RenderEngine as a texture.

 *

 * A typical usage pattern is to set up the BufferLayerConsumer with the

 * desired options, and call updateTexImage() when a new frame is desired.

 * If a new frame is available, the texture will be updated.  If not,

 * the previous contents are retained.

 * A typical usage pattern is to call updateTexImage() when a new frame is

 * desired.  If a new frame is available, the frame is latched.  If not, the

 * previous contents are retained.  The texture is attached and updated after

 * bindTextureImage() is called.

 *

 * The texture is attached to the GL_TEXTURE_EXTERNAL_OES texture target, in

 * the EGL context of the first thread that calls updateTexImage(). After that

 * point, all calls to updateTexImage must be made with the same OpenGL ES

 * context current.

 *

 * This class was previously called SurfaceTexture.

 * All calls to updateTexImage must be made with RenderEngine being current.

 * The texture is attached to the TEXTURE_EXTERNAL texture target.

 */

class BufferLayerConsumer : public ConsumerBase {

public:

        virtual void onSidebandStreamChanged() = 0;

    };

    // BufferLayerConsumer constructs a new BufferLayerConsumer object.

    // The tex parameter indicates the name of the OpenGL ES

    // texture to which images are to be streamed.

    // BufferLayerConsumer constructs a new BufferLayerConsumer object.  The

    // tex parameter indicates the name of the RenderEngine texture to which

    // images are to be streamed.

    BufferLayerConsumer(const sp<IGraphicBufferConsumer>& bq, RenderEngine& engine, uint32_t tex,

                        Layer* layer);

    // updateTexImage acquires the most recently queued buffer, and sets the

    // image contents of the target texture to it.

    //

    // This call may only be made while the OpenGL ES context to which the

    // target texture belongs is bound to the calling thread.

    // This call may only be made while RenderEngine is current.

    //

    // This calls doFenceWait to ensure proper synchronization.

    // This calls doFenceWait to ensure proper synchronization unless native

    // fence is supported.

    //

    // This version of updateTexImage() takes a functor that may be used to

    // reject the newly acquired buffer.  Unlike the GLConsumer version,

    // this does not guarantee that the buffer has been bound to the GL

    // texture.

    // Unlike the GLConsumer version, this version takes a functor that may be

    // used to reject the newly acquired buffer.  It also does not bind the

    // RenderEngine texture until bindTextureImage is called.

    status_t updateTexImage(BufferRejecter* rejecter, const DispSync& dispSync, bool* autoRefresh,

                            bool* queuedBuffer, uint64_t maxFrameNumber);

    sp<Fence> getPrevFinalReleaseFence() const;

    // getTransformMatrix retrieves the 4x4 texture coordinate transform matrix

    // associated with the texture image set by the most recent call to

    // updateTexImage.

    //

    // This transform matrix maps 2D homogeneous texture coordinates of the form

    // (s, t, 0, 1) with s and t in the inclusive range [0, 1] to the texture

    // coordinate that should be used to sample that location from the texture.

    // Sampling the texture outside of the range of this transform is undefined.

    //

    // This transform is necessary to compensate for transforms that the stream

    // content producer may implicitly apply to the content. By forcing users of

    // a BufferLayerConsumer to apply this transform we avoid performing an extra

    // copy of the data that would be needed to hide the transform from the

    // user.

    //

    // The matrix is stored in column-major order so that it may be passed

    // directly to OpenGL ES via the glLoadMatrixf or glUniformMatrix4fv

    // functions.

    // See GLConsumer::getTransformMatrix.

    void getTransformMatrix(float mtx[16]);

    // getTimestamp retrieves the timestamp associated with the texture image

    // must be called from SF main thread

    const Region& getSurfaceDamage() const;

    // setDefaultBufferSize is used to set the size of buffers returned by

    // requestBuffers when a with and height of zero is requested.

    // A call to setDefaultBufferSize() may trigger requestBuffers() to

    // be called from the client.

    // The width and height parameters must be no greater than the minimum of

    // GL_MAX_VIEWPORT_DIMS and GL_MAX_TEXTURE_SIZE (see: glGetIntegerv).

    // An error due to invalid dimensions might not be reported until

    // updateTexImage() is called.

    // See GLConsumer::setDefaultBufferSize.

    status_t setDefaultBufferSize(uint32_t width, uint32_t height);

    // setFilteringEnabled sets whether the transform matrix should be computed

    };

    // freeBufferLocked frees up the given buffer slot. If the slot has been

    // initialized this will release the reference to the GraphicBuffer in that

    // slot and destroy the EGLImage in that slot.  Otherwise it has no effect.

    // initialized this will release the reference to the GraphicBuffer in

    // that slot and destroy the RE::Image in that slot.  Otherwise it has no

    // effect.

    //

    // This method must be called with mMutex locked.

    virtual void freeBufferLocked(int slotIndex);

    RenderEngine& mRE;

    // mTexName is the name of the OpenGL texture to which streamed images will

    // be bound when updateTexImage is called. It is set at construction time.

    // mTexName is the name of the RenderEngine texture to which streamed

    // images will be bound when bindTexImage is called. It is set at

    // construction time.

    const uint32_t mTexName;

    // The layer for this BufferLayerConsumer

    sp<Image> mImages[BufferQueueDefs::NUM_BUFFER_SLOTS];

    // mCurrentTexture is the buffer slot index of the buffer that is currently

    // bound to the OpenGL texture. It is initialized to INVALID_BUFFER_SLOT,

    // bound to the RenderEngine texture. It is initialized to INVALID_BUFFER_SLOT,

    // indicating that no buffer slot is currently bound to the texture. Note,

    // however, that a value of INVALID_BUFFER_SLOT does not necessarily mean

    // that no buffer is bound to the texture. A call to setBufferCount will