Change the caret color according to the lightness of the background color.

Source/WebCore/editing/FrameSelection.cpp

Index: Source/WebCore/editing/FrameSelection.cpp
diff --git a/Source/WebCore/editing/FrameSelection.cpp b/Source/WebCore/editing/FrameSelection.cpp
index 059f0352a4f433829554256c1a3144d608947837..32c0eaf58e5ad33f80e246acca03a27c83e691c7 100644
--- a/Source/WebCore/editing/FrameSelection.cpp
+++ b/Source/WebCore/editing/FrameSelection.cpp
@@ -1444,9 +1444,29 @@ void CaretBase::paintCaret(Node* node, GraphicsContext* context, const LayoutPoi
 
     Color caretColor = Color::black;
     ColorSpace colorSpace = ColorSpaceDeviceRGB;
-    Element* element = node->rootEditableElement();
+    Element* element = static_cast<Element *>(node);
     if (element && element->renderer()) {
-        caretColor = element->renderer()->style()->visitedDependentColor(CSSPropertyColor);

[eseidel, 2013/04/18 16:03:16]

I'm confused.  This is clearly not always black, as you noted above?

[joone, 2013/04/19 00:25:22]

Yes, the caret color is not always black. I misunderstood how the caret color is
painted. The caret color is determined by the color of the root editable
element(the topmost parent or the element itself)

+        bool isTransparentPage = true;
+        RenderObject* renderer = element->renderer();
+        while (renderer) {
+            if (renderer->style()->hasBackground()) {

[eseidel, 2013/04/18 16:03:16]

I'm not sure what it means to be a transparent page.  RenderView always paints a
background, no?

[joone, 2013/04/19 00:25:22]

Yes, RenderView paints the background with FrameView's background color that is
white, so the variable name should be changed to isWhitePage or
isWhiteBackground.

[joone, 2013/04/26 19:12:55]

How about isBackgroundWhite instead of isTransparentPage?

+                isTransparentPage = false;
+                break;
+            }
+            if (!renderer->isRoot())
+                renderer = renderer->parent();
+            else
+                break;
+        }
+
+        Color backgroundColor;
+        if (!isTransparentPage) {
+            backgroundColor = renderer->style()->visitedDependentColor(CSSPropertyBackgroundColor);
+            if (backgroundColor.lightness() < 0.5)
+                caretColor = Color::white;
+        } else
+            caretColor = Color::black;
+
         colorSpace = element->renderer()->style()->colorSpace();
     }