从handle得到GraphicBuffer

先定义一个宏：

#ifndef container_of
#define container_of(ptr, type, member) \
    (type *)((char*)(ptr) - offsetof(type, member))
#endif

然后：

ANativeWindowBuffer *anwBuffer = container_of(buffer, ANativeWindowBuffer, handle);

其中buffer的类型是：

buffer_handle_t *buffer;

得到ANativeWindowBuffer以后：

sp GraphicBuffer::from(ANativeWindowBuffer* anwb) {
    return static_cast(anwb);
}