third_party/WebKit/Source/core/paint/BoxDecorationData.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/BoxDecorationData.h"

#include "core/layout/LayoutBox.h"
#include "core/paint/BoxPainter.h"
#include "core/style/BorderEdge.h"
#include "core/style/ComputedStyle.h"
#include "platform/RuntimeEnabledFeatures.h"
#include "platform/graphics/GraphicsContext.h"

namespace blink {

BoxDecorationData::BoxDecorationData(const LayoutBox& layoutBox) {
  backgroundColor =
      layoutBox.style()->visitedDependentColor(CSSPropertyBackgroundColor);
  hasBackground =
      backgroundColor.alpha() || layoutBox.style()->hasBackgroundImage();
  ASSERT(hasBackground == layoutBox.style()->hasBackground());
  hasBorderDecoration = layoutBox.style()->hasBorderDecoration();
  hasAppearance = layoutBox.style()->hasAppearance();
  bleedAvoidance = determineBackgroundBleedAvoidance(layoutBox);
}

namespace {

bool borderObscuresBackgroundEdge(const ComputedStyle& style) {
  BorderEdge edges[4];
  style.getBorderEdgeInfo(edges);

  for (auto& edge : edges) {
    if (!edge.obscuresBackgroundEdge())
      return false;
  }

  return true;
}

}  // anonymous namespace

BackgroundBleedAvoidance BoxDecorationData::determineBackgroundBleedAvoidance(
    const LayoutBox& layoutBox) {
  if (layoutBox.isDocumentElement())
    return BackgroundBleedNone;

  if (!hasBackground)
    return BackgroundBleedNone;

  const ComputedStyle& boxStyle = layoutBox.styleRef();
  const bool hasBorderRadius = boxStyle.hasBorderRadius();
  if (!hasBorderDecoration || !hasBorderRadius ||
      layoutBox.canRenderBorderImage()) {
    if (layoutBox.backgroundShouldAlwaysBeClipped())
      return BackgroundBleedClipOnly;
    // Border radius clipping may require layer bleed avoidance if we are going
    // to draw an image over something else, because we do not want the
    // antialiasing to lead to bleeding
    if (boxStyle.hasBackgroundImage() && hasBorderRadius) {
      // But if the top layer is opaque for the purposes of background painting,
      // we do not need the bleed avoidance because we will not paint anything
      // behind the top layer.  But only if we need to draw something
      // underneath.
      const FillLayer& fillLayer = layoutBox.style()->backgroundLayers();
      if ((backgroundColor.alpha() || fillLayer.next()) &&
          !fillLayer.imageOccludesNextLayers(layoutBox))
        return BackgroundBleedClipLayer;
    }
    return BackgroundBleedNone;
  }

  if (borderObscuresBackgroundEdge(boxStyle))
    return BackgroundBleedShrinkBackground;

  return BackgroundBleedClipLayer;
}

}  // namespace blink