Better handling border color style decoration

Source/core/paint/ObjectPainter.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/ObjectPainter.h"
 
 #include "core/paint/DrawingRecorder.h"
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderObject.h"
@@ skipping 116 matching lines @@
     case DOUBLE:
         drawDoubleBoxSide(graphicsContext, x1, y1, x2, y2, length, side, color,
             thickness, adjacentWidth1, adjacentWidth2, antialias);
         break;
     case RIDGE:
     case GROOVE:
         drawRidgeOrGrooveBoxSide(graphicsContext, x1, y1, x2, y2, side, color,
             style, adjacentWidth1, adjacentWidth2, antialias);
         break;
     case INSET:
-        // FIXME: Maybe we should lighten the colors on one side like Firefox.
-        // https://bugs.webkit.org/show_bug.cgi?id=58608
-        if (side == BSTop || side == BSLeft)
-            color = color.dark();
-        // fall through
     case OUTSET:
-        if (style == OUTSET && (side == BSBottom || side == BSRight))
-            color = color.dark();
+        modifyBorderColorForStyleIfNeeded(style, side, color);
         // fall through
     case SOLID:
         drawSolidBoxSide(graphicsContext, x1, y1, x2, y2, side, color, adjacentWidth1, adjacentWidth2, antialias);
         break;
     }
 }
 
 void ObjectPainter::drawDashedOrDottedBoxSide(GraphicsContext* graphicsContext, int x1, int y1, int x2, int y2,
     BoxSide side, Color color, int thickness, EBorderStyle style, bool antialias)
 {
@@ skipping 183 matching lines @@
         quad[0] = FloatPoint(x1, y1 + std::max(adjacentWidth1, 0));
         quad[1] = FloatPoint(x1, y2 - std::max(adjacentWidth2, 0));
         quad[2] = FloatPoint(x2, y2 - std::max(-adjacentWidth2, 0));
         quad[3] = FloatPoint(x2, y1 + std::max(-adjacentWidth1, 0));
         break;
     }
 
     graphicsContext->fillPolygon(4, quad, color, antialias);
 }
 
+void ObjectPainter::modifyBorderColorForStyleIfNeeded(const EBorderStyle& style, const BoxSide& side, Color& color)
+{
+    const RGBA32 baseDarkColor = 0xFF202020;

[chrishtr, 2014/12/01 22:51:31]

This needs a comment explaining where these numbers come from. Please link to
the spec it came from.

+    const RGBA32 baseLightColor = 0xFFEBEBEB;
+    enum Operation { Darken, Lighten };
+    Operation operation = (side == BSTop || side == BSLeft) == (style == INSET) ?
+        Darken : Lighten;
+
+    if (operation == Darken) {
+        if (differenceSquared(color, Color::black) >
+            differenceSquared(baseDarkColor, Color::black)) {

[pdr., 2014/12/02 02:55:49]

differenceSquared(baseDarkColor, Color::black) and
differenceSquared(baseLightColor, Color::white) are constant so we should be
able to compute them ahead of time.

+            color = color.dark();
+        }
+    } else {
+        if (differenceSquared(color, Color::white) >
+            differenceSquared(baseLightColor, Color::white)) {
+            color = color.light();
+        }
+    }
+}
+
 } // namespace blink