Better handling border color style decoration

Source/core/paint/ObjectPainter.cpp

Index: Source/core/paint/ObjectPainter.cpp
diff --git a/Source/core/paint/ObjectPainter.cpp b/Source/core/paint/ObjectPainter.cpp
index 976976753229652d44e93f25d7aa2640f0b76bff..6d3521b5881086e219c32d58ef5bebed260a0af2 100644
--- a/Source/core/paint/ObjectPainter.cpp
+++ b/Source/core/paint/ObjectPainter.cpp
@@ -134,14 +134,8 @@ void ObjectPainter::drawLineForBoxSide(GraphicsContext* graphicsContext, int x1,
             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);
@@ -345,4 +339,25 @@ void ObjectPainter::drawSolidBoxSide(GraphicsContext* graphicsContext, int x1, i
     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