Factor painting code out of RenderBox into a new class called BoxPainter.

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 "config.h"
+#include "core/paint/BoxDecorationData.h"
+
+#include "core/rendering/style/BorderEdge.h"
+#include "core/rendering/style/RenderStyle.h"
+#include "platform/graphics/GraphicsContext.h"
+
+namespace blink {
+
+BoxDecorationData::BoxDecorationData(const RenderStyle& style, bool canRenderBorderImage, bool backgroundHasOpaqueTopLayer, GraphicsContext* context)
+{
+    backgroundColor = style.visitedDependentColor(CSSPropertyBackgroundColor);
+    hasBackground = backgroundColor.alpha() || style.hasBackgroundImage();
+    ASSERT(hasBackground == style.hasBackground());
+    hasBorder = style.hasBorder();
+    hasAppearance = style.hasAppearance();
+
+    m_bleedAvoidance = determineBackgroundBleedAvoidance(style, canRenderBorderImage, backgroundHasOpaqueTopLayer, context);
+}
+
+BackgroundBleedAvoidance BoxDecorationData::determineBackgroundBleedAvoidance(const RenderStyle& style, bool canRenderBorderImage, bool backgroundHasOpaqueTopLayer, GraphicsContext* context)
+{
+    if (!hasBackground || !hasBorder || !style.hasBorderRadius() || canRenderBorderImage)
+        return BackgroundBleedNone;
+
+    // FIXME: See crbug.com/382491. getCTM does not accurately reflect the scale at the time content is
+    // rasterized, and should not be relied on to make decisions about bleeding.
+    AffineTransform ctm = context->getCTM();
+    FloatSize contextScaling(static_cast<float>(ctm.xScale()), static_cast<float>(ctm.yScale()));
+
+    // Because RoundedRect uses IntRect internally the inset applied by the
+    // BackgroundBleedShrinkBackground strategy cannot be less than one integer
+    // layout coordinate, even with subpixel layout enabled. To take that into
+    // account, we clamp the contextScaling to 1.0 for the following test so
+    // that borderObscuresBackgroundEdge can only return true if the border
+    // widths are greater than 2 in both layout coordinates and screen
+    // coordinates.
+    // This precaution will become obsolete if RoundedRect is ever promoted to
+    // a sub-pixel representation.
+    if (contextScaling.width() > 1)
+        contextScaling.setWidth(1);
+    if (contextScaling.height() > 1)
+        contextScaling.setHeight(1);
+
+    if (borderObscuresBackgroundEdge(style, contextScaling))
+        return BackgroundBleedShrinkBackground;
+    if (!hasAppearance && style.borderObscuresBackground() && backgroundHasOpaqueTopLayer)
+        return BackgroundBleedBackgroundOverBorder;
+
+    return BackgroundBleedClipBackground;
+}
+
+bool BoxDecorationData::borderObscuresBackgroundEdge(const RenderStyle& style, const FloatSize& contextScale) const
+{
+    BorderEdge edges[4];
+    style.getBorderEdgeInfo(edges);
+
+    for (int i = BSTop; i <= BSLeft; ++i) {
+        const BorderEdge& currEdge = edges[i];
+        // FIXME: for vertical text
+        float axisScale = (i == BSTop || i == BSBottom) ? contextScale.height() : contextScale.width();
+        if (!currEdge.obscuresBackgroundEdge(axisScale))
+            return false;
+    }
+
+    return true;
+}
+
+} // namespace blink