[CSS Blending] Implement mix-blend-mode in software.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 114 matching lines @@
     , m_hasUnclippedDescendant(false)
     , m_isUnclippedDescendant(false)
     , m_needsCompositedScrolling(false)
     , m_needsCompositedScrollingHasBeenRecorded(false)
     , m_willUseCompositedScrollingHasBeenRecorded(false)
     , m_isScrollableAreaHasBeenRecorded(false)
     , m_canBePromotedToStackingContainer(false)
     , m_canBePromotedToStackingContainerDirty(true)
     , m_isRootLayer(renderer->isRenderView())
     , m_usedTransparency(false)
+    , m_childLayerHasBlendMode(false)
+    , m_childLayerHasBlendModeStatusDirty(false)
     , m_paintingInsideReflection(false)
     , m_repaintStatus(NeedsNormalRepaint)
     , m_visibleContentStatusDirty(true)
     , m_hasVisibleContent(false)
     , m_visibleDescendantStatusDirty(false)
     , m_hasVisibleDescendant(false)
     , m_isPaginated(false)
     , m_3DTransformedDescendantStatusDirty(true)
     , m_has3DTransformedDescendant(false)
     , m_containsDirtyOverlayScrollbars(false)
@@ skipping 671 matching lines @@
 bool RenderLayer::hasBlendMode() const
 {
     return RuntimeEnabledFeatures::cssCompositingEnabled() && renderer()->hasBlendMode();
 }
 
 void RenderLayer::updateBlendMode()
 {
     if (!RuntimeEnabledFeatures::cssCompositingEnabled())
         return;
 
+    bool hadBlendMode = m_blendMode != BlendModeNormal;

[Julien - ping for review, 2013/09/30 17:59:11]

Unused variable.

+
     BlendMode newBlendMode = renderer()->style()->blendMode();
     if (newBlendMode != m_blendMode) {
         m_blendMode = newBlendMode;
+
+        setAncestorChainBlendedDescendant();

[Julien - ping for review, 2013/09/30 17:59:11]

I don't think this logic is right: you should only call it if you *do* have a
blend mode, which is not guaranteed if you come here (the only condition you
check is whether you have changed).

Btw, this should be tested.

[mitica, 2013/10/01 13:14:37]

You are right, I missed this. The new approach will imply modifying the flags
only if a blend mode is set or unset. In other words, if the style already has
blendMode set to Multiply, and this changes to Hue, the flag doesn't need to be
updated. I'll also add a repaint test that validates the mechanism

+
         if (backing())
             backing()->setBlendMode(newBlendMode);
     }
 }
 
 void RenderLayer::updateTransform()
 {
     // hasTransform() on the renderer is also true when there is transform-style: preserve-3d or perspective set,
     // so check style too.
     bool hasTransform = renderer()->hasTransform() && renderer()->style()->hasTransform();
@@ skipping 212 matching lines @@
 {
     for (RenderLayer* layer = this; layer; layer = layer->parent()) {
         if (!layer->m_visibleDescendantStatusDirty && layer->hasVisibleDescendant())
             break;
 
         layer->m_hasVisibleDescendant = true;
         layer->m_visibleDescendantStatusDirty = false;
     }
 }
 
+void RenderLayer::dirtyAncestorChainBlendedDescendantStatus()
+{
+    for (RenderLayer* layer = this; layer; layer = layer->parent()) {
+        if (layer->m_childLayerHasBlendModeStatusDirty)
+            break;
+
+        layer->m_childLayerHasBlendModeStatusDirty = true;
+
+        if (layer->isStackingContext())
+            break;
+    }
+}
+
+void RenderLayer::setAncestorChainBlendedDescendant()
+{
+    for (RenderLayer* layer = this; layer; layer = layer->parent()) {
+        if (!layer->m_childLayerHasBlendModeStatusDirty && layer->m_childLayerHasBlendMode)
+            break;
+
+        layer->m_childLayerHasBlendMode = true;
+        layer->m_childLayerHasBlendModeStatusDirty = false;
+
+        if (layer->isStackingContext())
+            break;
+    }
+}
+
 void RenderLayer::updateHasUnclippedDescendant()
 {
     TRACE_EVENT0("blink_rendering", "RenderLayer::updateHasUnclippedDescendant");
     ASSERT(renderer()->isOutOfFlowPositioned());
     if (!m_hasVisibleContent && !m_hasVisibleDescendant)
         return;
 
     FrameView* frameView = renderer()->view()->frameView();
     if (!frameView)
         return;
@@ skipping 39 matching lines @@
 
             if (m_hasVisibleDescendant && m_hasSelfPaintingLayerDescendant && hasOutOfFlowPositionedDescendant)
                 break;
         }
 
         m_visibleDescendantStatusDirty = false;
         m_hasSelfPaintingLayerDescendantDirty = false;
         m_hasOutOfFlowPositionedDescendantDirty = false;
     }
 
+    if (m_childLayerHasBlendModeStatusDirty) {
+        for (RenderLayer* child = firstChild(); child; child = child->nextSibling()) {
+            child->updateDescendantDependentFlags();
+            if (child->hasBlendMode() || child->isStackingContext())
+                break;
+
+            bool childLayerHasBlendMode = child->hasBlendMode() || child->m_childLayerHasBlendMode;
+            m_childLayerHasBlendMode |= childLayerHasBlendMode;
+        }
+        m_childLayerHasBlendModeStatusDirty = false;
+    }
+
     if (m_visibleContentStatusDirty) {
         if (renderer()->style()->visibility() == VISIBLE)
             m_hasVisibleContent = true;
         else {
             // layer may be hidden but still have some visible content, check for this
             m_hasVisibleContent = false;
             RenderObject* r = renderer()->firstChild();
             while (r) {
                 if (r->style()->visibility() == VISIBLE && !r->hasLayer()) {
                     m_hasVisibleContent = true;
@@ skipping 555 matching lines @@
     return clipRect;
 }
 
 LayoutRect RenderLayer::paintingExtent(const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, PaintBehavior paintBehavior)
 {
     return intersection(transparencyClipBox(this, rootLayer, PaintingTransparencyClipBox, RootOfTransparencyClipBox, paintBehavior), paintDirtyRect);
 }
 
 void RenderLayer::beginTransparencyLayers(GraphicsContext* context, const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, PaintBehavior paintBehavior)
 {
-    if (context->paintingDisabled() || (paintsWithTransparency(paintBehavior) && m_usedTransparency))
+    bool createTransparencyLayerForBlendMode = isStackingContext() && m_childLayerHasBlendMode;
+    if (context->paintingDisabled() || ((paintsWithTransparency(paintBehavior) || hasBlendMode() || createTransparencyLayerForBlendMode) && m_usedTransparency))
         return;
 
     RenderLayer* ancestor = transparentPaintingAncestor();
     if (ancestor)
         ancestor->beginTransparencyLayers(context, rootLayer, paintDirtyRect, paintBehavior);
 
-    if (paintsWithTransparency(paintBehavior)) {
+    if (paintsWithTransparency(paintBehavior) || hasBlendMode() || createTransparencyLayerForBlendMode) {
         m_usedTransparency = true;
         context->save();
         LayoutRect clipRect = paintingExtent(rootLayer, paintDirtyRect, paintBehavior);
         context->clip(clipRect);
+        if (hasBlendMode())
+            context->setCompositeOperation(context->compositeOperation(), m_blendMode);
+
         context->beginTransparencyLayer(renderer()->opacity());
 #ifdef REVEAL_TRANSPARENCY_LAYERS
         context->setFillColor(Color(0.0f, 0.0f, 0.5f, 0.2f));
         context->fillRect(clipRect);
 #endif
     }
 }
 
 void* RenderLayer::operator new(size_t sz)
 {
@@ skipping 34 matching lines @@
         child->dirtyStackingContainerZOrderLists();
     }
 
     child->updateDescendantDependentFlags();
     if (child->m_hasVisibleContent || child->m_hasVisibleDescendant)
         setAncestorChainHasVisibleDescendant();
 
     if (child->isSelfPaintingLayer() || child->hasSelfPaintingLayerDescendant())
         setAncestorChainHasSelfPaintingLayerDescendant();
 
+    if (child->hasBlendMode() || child->m_childLayerHasBlendMode)

[Julien - ping for review, 2013/09/30 17:59:11]

You can potentially check a dirty value here. You should expose a helper
function that ASSERT that we don't query a dirtied value and transition all
checks to use it.

If you can't have the ASSERT, it's still important to document it (see
hasSelfPaintingLayerDescendant).

[mitica, 2013/10/01 13:14:37]

Indeed, thanks for pointing this out, I'll add the assert :)

+        setAncestorChainBlendedDescendant();
+
     if (subtreeContainsOutOfFlowPositionedLayer(child)) {
         // Now that the out of flow positioned descendant is in the tree, we
         // need to tell the compositor to reevaluate the compositing
         // requirements since we may be able to mark more layers as having
         // an 'unclipped' descendant.
         compositor()->setNeedsUpdateCompositingRequirementsState();
         setAncestorChainHasOutOfFlowPositionedDescendant();
     }
 
     // When we first dirty a layer, we will also dirty all the siblings in that
@@ skipping 41 matching lines @@
         compositor()->setNeedsUpdateCompositingRequirementsState();
         dirtyAncestorChainHasOutOfFlowPositionedDescendantStatus();
     }
 
     if (oldChild->m_hasVisibleContent || oldChild->m_hasVisibleDescendant)
         dirtyAncestorChainVisibleDescendantStatus();
 
     if (oldChild->isSelfPaintingLayer() || oldChild->hasSelfPaintingLayerDescendant())
         dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
+    if (oldChild->hasBlendMode() || oldChild->m_childLayerHasBlendMode)

[Julien - ping for review, 2013/09/30 17:59:11]

Ditto.

+        dirtyAncestorChainBlendedDescendantStatus();
+
     return oldChild;
 }
 
 void RenderLayer::removeOnlyThisLayer()
 {
     if (!m_parent)
         return;
 
     // Mark that we are about to lose our layer. This makes render tree
     // walks ignore this layer while we're removing it.
@@ skipping 1379 matching lines @@
 
                 resourceClipper = toRenderSVGResourceClipper(element->renderer()->toRenderSVGResourceContainer());
                 if (!resourceClipper->applyClippingToContext(renderer(), rootRelativeBounds, paintingInfo.paintDirtyRect, context)) {
                     // No need to post-apply the clipper if this failed.
                     resourceClipper = 0;
                 }
             }
         }
     }
 
+    // Blending operations must be performed only with the nearest ancestor stacking context.
+    bool createTransparencyLayerForBlendMode = isStackingContext() && m_childLayerHasBlendMode;
+
+    if (createTransparencyLayerForBlendMode)
+        beginTransparencyLayers(context, paintingInfo.rootLayer, paintingInfo.paintDirtyRect, paintingInfo.paintBehavior);
+
     LayerPaintingInfo localPaintingInfo(paintingInfo);
     FilterEffectRendererHelper filterPainter(filterRenderer() && paintsWithFilters());
     if (filterPainter.haveFilterEffect() && !context->paintingDisabled()) {
         RenderLayerFilterInfo* filterInfo = this->filterInfo();
         ASSERT(filterInfo);
         LayoutRect filterRepaintRect = filterInfo->dirtySourceRect();
         filterRepaintRect.move(offsetFromRoot.x(), offsetFromRoot.y());
 
         if (!rootRelativeBoundsComputed) {
             rootRelativeBounds = calculateLayerBounds(paintingInfo.rootLayer, &offsetFromRoot, 0);
@@ skipping 101 matching lines @@
 
     if (shouldPaintMask)
         paintMaskForFragments(layerFragments, context, localPaintingInfo, paintingRootForRenderer);
 
     if (shouldPaintClippingMask) {
         // Paint the border radius mask for the fragments.
         paintChildClippingMaskForFragments(layerFragments, context, localPaintingInfo, paintingRootForRenderer);
     }
 
     // End our transparency layer
-    if (haveTransparency && m_usedTransparency && !m_paintingInsideReflection) {
+    if ((haveTransparency || hasBlendMode() || createTransparencyLayerForBlendMode) && m_usedTransparency && !m_paintingInsideReflection) {
         context->endLayer();
         context->restore();
         m_usedTransparency = false;
     }
 
     if (resourceClipper)
         resourceClipper->postApplyResource(renderer(), context, ApplyToDefaultMode, 0, 0);
 
     if (hasClipPath)
         context->restore();
@@ skipping 164 matching lines @@
 void RenderLayer::paintBackgroundForFragments(const LayerFragments& layerFragments, GraphicsContext* context, GraphicsContext* transparencyLayerContext,
     const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo& localPaintingInfo, PaintBehavior paintBehavior,
     RenderObject* paintingRootForRenderer)
 {
     for (size_t i = 0; i < layerFragments.size(); ++i) {
         const LayerFragment& fragment = layerFragments.at(i);
         if (!fragment.shouldPaintContent)
             continue;
 
         // Begin transparency layers lazily now that we know we have to paint something.
-        if (haveTransparency)
+        if (haveTransparency || hasBlendMode())
             beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, transparencyPaintDirtyRect, localPaintingInfo.paintBehavior);
 
         if (localPaintingInfo.clipToDirtyRect) {
             // Paint our background first, before painting any child layers.
             // Establish the clip used to paint our background.
             clipToRect(localPaintingInfo.rootLayer, context, localPaintingInfo.paintDirtyRect, fragment.backgroundRect, DoNotIncludeSelfForBorderRadius); // Background painting will handle clipping to self.
         }
 
         // Paint the background.
         // FIXME: Eventually we will collect the region from the fragment itself instead of just from the paint info.
         PaintInfo paintInfo(context, pixelSnappedIntRect(fragment.backgroundRect.rect()), PaintPhaseBlockBackground, paintBehavior, paintingRootForRenderer, localPaintingInfo.region, 0, 0, localPaintingInfo.rootLayer->renderer());
         renderer()->paint(paintInfo, toPoint(fragment.layerBounds.location() - renderBoxLocation() + localPaintingInfo.subPixelAccumulation));
 
         if (localPaintingInfo.clipToDirtyRect)
             restoreClip(context, localPaintingInfo.paintDirtyRect, fragment.backgroundRect);
     }
 }
 
 void RenderLayer::paintForegroundForFragments(const LayerFragments& layerFragments, GraphicsContext* context, GraphicsContext* transparencyLayerContext,
     const LayoutRect& transparencyPaintDirtyRect, bool haveTransparency, const LayerPaintingInfo& localPaintingInfo, PaintBehavior paintBehavior,
     RenderObject* paintingRootForRenderer, bool selectionOnly, bool forceBlackText)
 {
     // Begin transparency if we have something to paint.
-    if (haveTransparency) {
+    if (haveTransparency || hasBlendMode()) {
         for (size_t i = 0; i < layerFragments.size(); ++i) {
             const LayerFragment& fragment = layerFragments.at(i);
             if (fragment.shouldPaintContent && !fragment.foregroundRect.isEmpty()) {
                 beginTransparencyLayers(transparencyLayerContext, localPaintingInfo.rootLayer, transparencyPaintDirtyRect, localPaintingInfo.paintBehavior);
                 break;
             }
         }
     }
 
     PaintBehavior localPaintBehavior = forceBlackText ? (PaintBehavior)PaintBehaviorForceBlackText : paintBehavior;
@@ skipping 2459 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif