third_party/WebKit/Source/core/paint/LayerClipRecorder.cpp

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "core/paint/LayerClipRecorder.h"

#include "core/layout/ClipRect.h"
#include "core/layout/LayoutView.h"
#include "core/paint/PaintLayer.h"
#include "platform/geometry/IntRect.h"
#include "platform/graphics/GraphicsContext.h"
#include "platform/graphics/GraphicsLayer.h"
#include "platform/graphics/paint/ClipRecorder.h"
#include "platform/graphics/paint/PaintController.h"

namespace blink {

LayerClipRecorder::LayerClipRecorder(GraphicsContext& graphicsContext,
                                     const LayoutBoxModelObject& layoutObject,
                                     DisplayItem::Type clipType,
                                     const ClipRect& clipRect,
                                     const PaintLayer* clipRoot,
                                     const LayoutPoint& fragmentOffset,
                                     PaintLayerFlags paintFlags,
                                     BorderRadiusClippingRule rule)
    : m_graphicsContext(graphicsContext),
      m_layoutObject(layoutObject),
      m_clipType(clipType) {
  IntRect snappedClipRect = pixelSnappedIntRect(clipRect.rect());
  Vector<FloatRoundedRect> roundedRects;
  if (clipRoot && clipRect.hasRadius()) {
    collectRoundedRectClips(*layoutObject.layer(), clipRoot, graphicsContext,
                            fragmentOffset, paintFlags, rule, roundedRects);
  }

  m_graphicsContext.getPaintController().createAndAppend<ClipDisplayItem>(
      layoutObject, m_clipType, snappedClipRect, roundedRects);
}

static bool inContainingBlockChain(PaintLayer* startLayer,
                                   PaintLayer* endLayer) {
  if (startLayer == endLayer)
    return true;

  LayoutView* view = startLayer->layoutObject()->view();
  for (const LayoutBlock* currentBlock =
           startLayer->layoutObject()->containingBlock();
       currentBlock && currentBlock != view;
       currentBlock = currentBlock->containingBlock()) {
    if (currentBlock->layer() == endLayer)
      return true;
  }

  return false;
}

void LayerClipRecorder::collectRoundedRectClips(
    PaintLayer& paintLayer,
    const PaintLayer* clipRoot,
    GraphicsContext& context,
    const LayoutPoint& fragmentOffset,
    PaintLayerFlags paintFlags,
    BorderRadiusClippingRule rule,
    Vector<FloatRoundedRect>& roundedRectClips) {
  // If the clip rect has been tainted by a border radius, then we have to walk
  // up our layer chain applying the clips from any layers with overflow. The
  // condition for being able to apply these clips is that the overflow object
  // be in our containing block chain so we check that also.
  for (PaintLayer* layer = rule == IncludeSelfForBorderRadius
                               ? &paintLayer
                               : paintLayer.parent();
       layer; layer = layer->parent()) {
    // Composited scrolling layers handle border-radius clip in the compositor
    // via a mask layer. We do not want to apply a border-radius clip to the
    // layer contents itself, because that would require re-rastering every
    // frame to update the clip. We only want to make sure that the mask layer
    // is properly clipped so that it can in turn clip the scrolled contents in
    // the compositor.
    if (layer->needsCompositedScrolling() &&
        !(paintFlags & PaintLayerPaintingChildClippingMaskPhase ||
          paintFlags & PaintLayerPaintingAncestorClippingMaskPhase))
      break;

    if (layer->layoutObject()->hasOverflowClip() &&
        layer->layoutObject()->style()->hasBorderRadius() &&
        inContainingBlockChain(&paintLayer, layer)) {
      LayoutPoint delta(fragmentOffset);
      layer->convertToLayerCoords(clipRoot, delta);

      // The PaintLayer's size is pixel-snapped if it is a LayoutBox. We can't
      // use a pre-snapped border rect for clipping, since
      // getRoundedInnerBorderFor assumes it has not been snapped yet.
      LayoutSize size(layer->layoutBox()
                          ? toLayoutBox(layer->layoutObject())->size()
                          : LayoutSize(layer->size()));
      roundedRectClips.append(
          layer->layoutObject()->style()->getRoundedInnerBorderFor(
              LayoutRect(delta, size)));
    }

    if (layer == clipRoot)
      break;
  }
}

LayerClipRecorder::~LayerClipRecorder() {
  m_graphicsContext.getPaintController().endItem<EndClipDisplayItem>(
      m_layoutObject, DisplayItem::clipTypeToEndClipType(m_clipType));
}

}  // namespace blink