GraphicBuffer、AHardwareBuffer、ANativeWindowBuffer关系

共同点 ：

1. 其实三者都是同一个东西，AHardwareBuffer、ANativeWindowBuffer都是GraphicBuffer通过类型转换而来。

联系

1. GraphicBuffer 继承了ANativeWindowBuffer，所以可以直接通过static_cast<>类型转换成ANativeWindowBuffer，不过由于是多继承，所以转完有一个地址偏移（static_cast 自动完成），

偏移量为0x10（64位场景）大小，为GraphicBuffer父类对象RefBase大小（包括虚函数表指针8字节，成员变量 weakref_impl* const mRefs 8字节）

多继承、带虚函数的偏移，可以参考

https://joydig.com/cpp-base-pointer-offset-adjustment-for-multiple-inheritance/

2. AHardwareBuffer只是一个抽象的概念，没有具体类型，与GraphicBuffer 没有任何继承关系，所以只能通过reinterpret_cast 强制类型转换而来。

区别：

1. AHardwareBuffer 没有具体的类型，是个空结构体，类似于void 类型，aosp封装的那些AHardWareBuffer_XXX接口https://developer.android.com/ndk/reference/group/a-hardware-buffer，其实底层都是把AHardwareBuffer转回成 GraphicBuffer，再去调GraphicBuffer接口。

2. 关于地址： AHardwareBuffer 与GraphicBuffer相同，与ANativeWindowBuffer不同，所以前2者之间可以直接类型强转，与第三者不行，

3. 类型转换接口

 
/*
总之 
AHardwareBuffer <-----> GraphicBuffer
用reinterpret_cast<> 无地址偏移，直接强转
ANativeWindowBuffer <------> GraphicBuffer
用static_cast<>, 有地址偏移
AHardwareBuffer <------> ANativeWindowBuffer
需要先转成GraphicBuffer，再做第二次类型转换
**/
 
 
const GraphicBuffer* AHardwareBuffer_to_GraphicBuffer(const AHardwareBuffer* buffer) {
    return GraphicBuffer::fromAHardwareBuffer(buffer);
}
 
GraphicBuffer* AHardwareBuffer_to_GraphicBuffer(AHardwareBuffer* buffer) {
    return GraphicBuffer::fromAHardwareBuffer(buffer);
}
 
const ANativeWindowBuffer* AHardwareBuffer_to_ANativeWindowBuffer(const AHardwareBuffer* buffer) {
    return AHardwareBuffer_to_GraphicBuffer(buffer)->getNativeBuffer();
}
 
ANativeWindowBuffer* AHardwareBuffer_to_ANativeWindowBuffer(AHardwareBuffer* buffer) {
    return AHardwareBuffer_to_GraphicBuffer(buffer)->getNativeBuffer();
}
 
AHardwareBuffer* AHardwareBuffer_from_GraphicBuffer(GraphicBuffer* buffer) {
    return buffer->toAHardwareBuffer();
}
 
sp<GraphicBuffer> GraphicBuffer::from(ANativeWindowBuffer* anwb) {
    return static_cast<GraphicBuffer *>(anwb);
}
 
GraphicBuffer* GraphicBuffer::fromAHardwareBuffer(AHardwareBuffer* buffer) {
    return reinterpret_cast<GraphicBuffer*>(buffer);
}
 
GraphicBuffer const* GraphicBuffer::fromAHardwareBuffer(AHardwareBuffer const* buffer) {
    return reinterpret_cast<GraphicBuffer const*>(buffer);
}
 
AHardwareBuffer* GraphicBuffer::toAHardwareBuffer() {
    return reinterpret_cast<AHardwareBuffer*>(this);
}
 
AHardwareBuffer const* GraphicBuffer::toAHardwareBuffer() const {
    return reinterpret_cast<AHardwareBuffer const*>(this);
}
 
AHardwareBuffer* ANativeWindowBuffer_getHardwareBuffer(ANativeWindowBuffer* anwb) {
    return AHardwareBuffer_from_GraphicBuffer(static_cast<GraphicBuffer*>(anwb));
}
 
ANativeWindowBuffer* GraphicBuffer::getNativeBuffer() const
{
    return static_cast<ANativeWindowBuffer*>(
            const_cast<GraphicBuffer*>(this));
}