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

Source/WebCore/editing/FrameSelection.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1426 matching lines @@
     RenderObject* renderer = caretRenderer(node);
     if (renderer && renderer->isBox())
         toRenderBox(renderer)->flipForWritingMode(drawingRect);
     drawingRect.moveBy(roundedIntPoint(paintOffset));
     LayoutRect caret = intersection(drawingRect, clipRect);
     if (caret.isEmpty())
         return;
 
     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();
     }
 
     context->fillRect(caret, caretColor, colorSpace);
 }
 
 void FrameSelection::debugRenderer(RenderObject *r, bool selected) const
 {
     if (r->node()->isElementNode()) {
         Element* element = static_cast<Element *>(r->node());
@@ skipping 593 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const WebCore::FrameSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif