Support subpixel layout for borders.

third_party/WebKit/Source/core/style/BorderEdge.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/style/BorderEdge.h"
 
 namespace blink {
 
-BorderEdge::BorderEdge(int edgeWidth,
+BorderEdge::BorderEdge(float edgeWidth,
                        const Color& edgeColor,
                        EBorderStyle edgeStyle,
                        bool edgeIsPresent)
-    : width(edgeWidth),
-      color(edgeColor),
+    : color(edgeColor),
       isPresent(edgeIsPresent),
-      style(edgeStyle) {
+      style(edgeStyle),
+      m_width(edgeWidth) {

[pdr., 2017/01/27 20:28:44]

Can width be negative? If not, can you DCHECK that it's positive?

[Karl Øygard, 2017/02/10 12:53:18]

Done.

   if (style == BorderStyleDouble && edgeWidth < 3)
     style = BorderStyleSolid;
 }
 
-BorderEdge::BorderEdge()
-    : width(0), isPresent(false), style(BorderStyleHidden) {}
+BorderEdge::BorderEdge() : isPresent(false), style(BorderStyleHidden) {}
 
 bool BorderEdge::hasVisibleColorAndStyle() const {
   return style > BorderStyleHidden && color.alpha() > 0;
 }
 
 bool BorderEdge::shouldRender() const {
-  return isPresent && width && hasVisibleColorAndStyle();
+  return isPresent && m_width && hasVisibleColorAndStyle();
 }
 
 bool BorderEdge::presentButInvisible() const {
   return usedWidth() && !hasVisibleColorAndStyle();
 }
 
 bool BorderEdge::obscuresBackgroundEdge() const {
   if (!isPresent || color.hasAlpha() || style == BorderStyleHidden)
     return false;
 
   if (style == BorderStyleDotted || style == BorderStyleDashed)
     return false;
 
   return true;
 }
 
 bool BorderEdge::obscuresBackground() const {
   if (!isPresent || color.hasAlpha() || style == BorderStyleHidden)
     return false;
 
   if (style == BorderStyleDotted || style == BorderStyleDashed ||
       style == BorderStyleDouble)
     return false;
 
   return true;
 }
 
-int BorderEdge::usedWidth() const {
-  return isPresent ? width : 0;
+float BorderEdge::usedWidth() const {
+  return isPresent ? m_width : 0;
 }
 
-int BorderEdge::getDoubleBorderStripeWidth(DoubleBorderStripe stripe) const {
+float BorderEdge::getDoubleBorderStripeWidth(DoubleBorderStripe stripe) const {
   ASSERT(stripe == DoubleBorderStripeOuter ||
          stripe == DoubleBorderStripeInner);
 
-  // We need certain integer rounding results.
-  return stripe == DoubleBorderStripeOuter ? (usedWidth() + 1) / 3
-                                           : (usedWidth() * 2 + 1) / 3;
+  return roundf(stripe == DoubleBorderStripeOuter ? usedWidth() / 3
+                                                  : (usedWidth() * 2) / 3);
 }
 
 bool BorderEdge::sharesColorWith(const BorderEdge& other) const {
   return color == other.color;
 }
 
 }  // namespace blink