[Android] NDK 里 ANativeWindow 和 Surface 之间的关系

在MediaCodec里面可以看到 Configure 和 SetSurface 都是接收一个 sp<Surface> 入参的，而回归到 NDK 侧，则可以发现，传递给 AMediaCodec_Configure 和 AMediaCodec_SetSurface 的确是 ANativeWindow 指针，因此 ndk 里面必然进行了某种转换。

cpp 复制代码

EXPORT
media_status_t AMediaCodec_configure(
        AMediaCodec *mData,
        const AMediaFormat* format,
        ANativeWindow* window,
        AMediaCrypto *crypto,
        uint32_t flags) {
    sp<AMessage> nativeFormat;
    AMediaFormat_getFormat(format, &nativeFormat);
    // create our shallow copy, so we aren't victim to any later changes.
    sp<AMessage> dupNativeFormat = nativeFormat->dup();
    ALOGV("configure with format: %s", dupNativeFormat->debugString(0).c_str());
    sp<Surface> surface = NULL;
    if (window != NULL) {
        surface = (Surface*) window;
    }

    status_t err = mData->mCodec->configure(dupNativeFormat, surface,
            crypto ? crypto->mCrypto : NULL, flags);
    if (err != OK) {
        ALOGE("configure: err(%d), failed with format: %s",
              err, dupNativeFormat->debugString(0).c_str());
    }
    return translate_error(err);
}

cpp 复制代码

//prebuilts/vndk/v32/arm64/include/frameworks/native/libs/gui/include/gui/Surface.h


/*
 * An implementation of ANativeWindow that feeds graphics buffers into a
 * BufferQueue.
 *
 * This is typically used by programs that want to render frames through
 * some means (maybe OpenGL, a software renderer, or a hardware decoder)
 * and have the frames they create forwarded to SurfaceFlinger for
 * compositing.  For example, a video decoder could render a frame and call
 * eglSwapBuffers(), which invokes ANativeWindow callbacks defined by
 * Surface.  Surface then forwards the buffers through Binder IPC
 * to the BufferQueue's producer interface, providing the new frame to a
 * consumer such as GLConsumer.
 */
class Surface
    : public ANativeObjectBase<ANativeWindow, Surface, RefBase>

由此可见， Surface 类是 ANativeWindow 的子类。