Android 系统中AHardwareBuffer、ANativeWindowBuffer和GraphicBuffer的关系

Android Camera软件系统中，每路Stream的Buffer都是DMA-BUF，这种Buffer通常对外暴露的结构是ANativeWindowBuffer或GraphicBuffer（跨进程传递时用的native_handle_t），本文介绍Android系统中AHardwareBuffer、ANativeWindowBuffer和GraphicBuffer的关系。ANativeWindowBuffer、AHardwareBuffer都是GraphicBuffer通过类型转换而来，ANativeWindowBuffer对native_handle_t进行了封装。

ANativeWindowBuffer

ANativeWindowBuffer定义在nativebase.h头文件中。

frameworks/native/libs/nativebase/include/nativebase/nativebase.h

定义如下：

typedef struct ANativeWindowBuffer
{
#ifdef __cplusplus
    ANativeWindowBuffer() {
        common.magic = ANDROID_NATIVE_BUFFER_MAGIC;
        common.version = sizeof(ANativeWindowBuffer);
        memset(common.reserved, 0, sizeof(common.reserved));
    }

    // Implement the methods that sp<ANativeWindowBuffer> expects so that it
    // can be used to automatically refcount ANativeWindowBuffer's.
    void incStrong(const void* /*id*/) const {
        common.incRef(const_cast<android_native_base_t*>(&common));
    }
    void decStrong(const void* /*id*/) const {
        common.decRef(const_cast<android_native_base_t*>(&common));
    }
#endif

    struct android_native_base_t common;

    int width;
    int height;
    int stride;
    int format;
    int usage_deprecated;
    uintptr_t layerCount;

    void* reserved[1];

    const native_handle_t* handle;
    uint64_t usage;

    // we needed extra space for storing the 64-bit