Chromium M34上图像（IMG元素）的直接合成，不走NativeImageSkia::draw路径的相关代码

来源：互联网发布：胰腺炎apache评分表编辑：程序博客网时间：2024/06/03 17:54

// An image can be directly compositing if it's the sole content of the layer, and has no box decorations// that require painting. Direct compositing saves backing store.bool CompositedLayerMapping::isDirectlyCompositedImage() const{    RenderObject* renderObject = renderer();    if (!renderObject->isImage() || m_owningLayer->hasBoxDecorationsOrBackground() || renderObject->hasClip())        return false;    RenderImage* imageRenderer = toRenderImage(renderObject);    if (ImageResource* cachedImage = imageRenderer->cachedImage()) {        if (!cachedImage->hasImage())            return false;        Image* image = cachedImage->imageForRenderer(imageRenderer);        return image->isBitmapImage();    }    return false;}

void CompositedLayerMapping::contentChanged(ContentChangeType changeType){    if ((changeType == ImageChanged) && isDirectlyCompositedImage()) {        updateImageContents();        return;    }    if ((changeType == MaskImageChanged) && m_maskLayer) {        // The composited layer bounds relies on box->maskClipRect(), which changes        // when the mask image becomes available.        updateAfterLayout(CompositingChildrenOnly | IsUpdateRoot);    }    if ((changeType == CanvasChanged || changeType == CanvasPixelsChanged) && isAcceleratedCanvas(renderer())) {        m_graphicsLayer->setContentsNeedsDisplay();        return;    }}

void CompositedLayerMapping::updateImageContents(){    ASSERT(renderer()->isImage());    RenderImage* imageRenderer = toRenderImage(renderer());    ImageResource* cachedImage = imageRenderer->cachedImage();    if (!cachedImage)        return;    Image* image = cachedImage->imageForRenderer(imageRenderer);    if (!image)        return;    // We have to wait until the image is fully loaded before setting it on the layer.    if (!cachedImage->isLoaded())        return;    // This is a no-op if the layer doesn't have an inner layer for the image.    m_graphicsLayer->setContentsToImage(image);    bool isSimpleContainer = false;    updateDrawsContent(isSimpleContainer);

void GraphicsLayer::setContentsToImage(Image* image){    RefPtr<NativeImageSkia> nativeImage = image ? image->nativeImageForCurrentFrame() : 0;    if (nativeImage) {        if (!m_imageLayer) {            m_imageLayer = adoptPtr(Platform::current()->compositorSupport()->createImageLayer());            registerContentsLayer(m_imageLayer->layer());        }        m_imageLayer->setBitmap(nativeImage->bitmap());        m_imageLayer->layer()->setOpaque(image->currentFrameKnownToBeOpaque());        updateContentsRect();    } else {        if (m_imageLayer) {            unregisterContentsLayer(m_imageLayer->layer());            m_imageLayer.clear();        }    }    setContentsTo(m_imageLayer ? m_imageLayer->layer() : 0);}

M39上反而不是这个行为，都会走NativeImageSkia::draw。当然，M39上SlimmingPaint和Ganesh（GPU Rasterization）仍然在持续重构中。

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