status_t VirtualDisplaySurface::beginFrame(bool mustRecompose) {
    if (mDisplayId < 0)
        return NO_ERROR;

    mMustRecompose = mustRecompose;

    VDS_LOGW_IF(mDbgState != DBG_STATE_IDLE,
            "Unexpected beginFrame() in %s state", dbgStateStr());
    mDbgState = DBG_STATE_BEGUN;

    return refreshOutputBuffer();
}
status_t VirtualDisplaySurface::beginFrame() {
    if (mDisplayId < 0)
        return NO_ERROR;

    VDS_LOGW_IF(mDbgState != DBG_STATE_IDLE,
            "Unexpected beginFrame() in %s state", dbgStateStr());
    mDbgState = DBG_STATE_BEGUN;

    uint32_t transformHint, numPendingBuffers;
    mQueueBufferOutput.deflate(&mSinkBufferWidth, &mSinkBufferHeight,
            &transformHint, &numPendingBuffers);

    return refreshOutputBuffer();
}
status_t VirtualDisplaySurface::prepareFrame(CompositionType compositionType) {
    if (mDisplayId < 0)
        return NO_ERROR;

    VDS_LOGW_IF(mDbgState != DBG_STATE_BEGUN,
            "Unexpected prepareFrame() in %s state", dbgStateStr());
    mDbgState = DBG_STATE_PREPARED;

    mCompositionType = compositionType;
    if (sForceHwcCopy && mCompositionType == COMPOSITION_GLES) {
        // Some hardware can do RGB->YUV conversion more efficiently in hardware
        // controlled by HWC than in hardware controlled by the video encoder.
        // Forcing GLES-composed frames to go through an extra copy by the HWC
        // allows the format conversion to happen there, rather than passing RGB
        // directly to the consumer.
        //
        // On the other hand, when the consumer prefers RGB or can consume RGB
        // inexpensively, this forces an unnecessary copy.
        mCompositionType = COMPOSITION_MIXED;
    }

    if (mCompositionType != mDbgLastCompositionType) {
        VDS_LOGV("prepareFrame: composition type changed to %s",
                dbgCompositionTypeStr(mCompositionType));
        mDbgLastCompositionType = mCompositionType;
    }

    if (mCompositionType != COMPOSITION_GLES &&
            (mOutputFormat != mDefaultOutputFormat ||
             mOutputUsage != GRALLOC_USAGE_HW_COMPOSER)) {
        // We must have just switched from GLES-only to MIXED or HWC
        // composition. Stop using the format and usage requested by the GLES
        // driver; they may be suboptimal when HWC is writing to the output
        // buffer. For example, if the output is going to a video encoder, and
        // HWC can write directly to YUV, some hardware can skip a
        // memory-to-memory RGB-to-YUV conversion step.
        //
        // If we just switched *to* GLES-only mode, we'll change the
        // format/usage and get a new buffer when the GLES driver calls
        // dequeueBuffer().
        mOutputFormat = mDefaultOutputFormat;
        mOutputUsage = GRALLOC_USAGE_HW_COMPOSER;
        refreshOutputBuffer();
    }

    return NO_ERROR;
}
status_t VirtualDisplaySurface::dequeueBuffer(int* pslot, sp<Fence>* fence, bool async,
        uint32_t w, uint32_t h, uint32_t format, uint32_t usage) {
    VDS_LOGW_IF(mDbgState != DBG_STATE_PREPARED,
            "Unexpected dequeueBuffer() in %s state", dbgStateStr());
    mDbgState = DBG_STATE_GLES;

    VDS_LOGW_IF(!async, "EGL called dequeueBuffer with !async despite eglSwapInterval(0)");
    VDS_LOGV("dequeueBuffer %dx%d fmt=%d usage=%#x", w, h, format, usage);

    status_t result = NO_ERROR;
    Source source = fbSourceForCompositionType(mCompositionType);

    if (source == SOURCE_SINK) {

        if (mOutputProducerSlot < 0) {
            // Last chance bailout if something bad happened earlier. For example,
            // in a GLES configuration, if the sink disappears then dequeueBuffer
            // will fail, the GLES driver won't queue a buffer, but SurfaceFlinger
            // will soldier on. So we end up here without a buffer. There should
            // be lots of scary messages in the log just before this.
            VDS_LOGE("dequeueBuffer: no buffer, bailing out");
            return NO_MEMORY;
        }

        // We already dequeued the output buffer. If the GLES driver wants
        // something incompatible, we have to cancel and get a new one. This
        // will mean that HWC will see a different output buffer between
        // prepare and set, but since we're in GLES-only mode already it
        // shouldn't matter.

        usage |= GRALLOC_USAGE_HW_COMPOSER;
        const sp<GraphicBuffer>& buf = mProducerBuffers[mOutputProducerSlot];
        if ((usage & ~buf->getUsage()) != 0 ||
                (format != 0 && format != (uint32_t)buf->getPixelFormat()) ||
                (w != 0 && w != mSinkBufferWidth) ||
                (h != 0 && h != mSinkBufferHeight)) {
            VDS_LOGV("dequeueBuffer: dequeueing new output buffer: "
                    "want %dx%d fmt=%d use=%#x, "
                    "have %dx%d fmt=%d use=%#x",
                    w, h, format, usage,
                    mSinkBufferWidth, mSinkBufferHeight,
                    buf->getPixelFormat(), buf->getUsage());
            mOutputFormat = format;
            mOutputUsage = usage;
            result = refreshOutputBuffer();
            if (result < 0)
                return result;
        }
    }

    if (source == SOURCE_SINK) {
        *pslot = mOutputProducerSlot;
        *fence = mOutputFence;
    } else {
        int sslot;
        result = dequeueBuffer(source, format, usage, &sslot, fence);
        if (result >= 0) {
            *pslot = mapSource2ProducerSlot(source, sslot);
        }
    }
    return result;
}