From 961c31082cdf711a19f9149376ec17e1ef997b06 Mon Sep 17 00:00:00 2001
From: "L. David Baron" <dbaron@dbaron.org>
Date: Fri, 2 Apr 2010 18:58:25 -0700
Subject: [PATCH] Add function to nsStyleUtil for choosing the appropriate
 color from style data based on link visitedness.  (Bug 147777)  r=bzbarsky

---
 layout/generic/nsIFrame.h       |  6 ++++
 layout/style/nsStyleContext.cpp | 55 +++++++++++++++++++++++++++++++++
 layout/style/nsStyleContext.h   | 10 ++++++
 3 files changed, 71 insertions(+)

diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index 81a99cbe6ba..b18b1d1bfa8 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -722,6 +722,12 @@ public:
   #include "nsStyleStructList.h"
   #undef STYLE_STRUCT
 
+#ifdef _IMPL_NS_LAYOUT
+  /** Also forward GetVisitedDependentColor to the style context */
+  nscolor GetVisitedDependentColor(nsCSSProperty aProperty)
+    { return mStyleContext->GetVisitedDependentColor(aProperty); }
+#endif
+
   /**
    * These methods are to access any additional style contexts that
    * the frame may be holding. These are contexts that are children
diff --git a/layout/style/nsStyleContext.cpp b/layout/style/nsStyleContext.cpp
index 1b16c209c76..5306f963e44 100644
--- a/layout/style/nsStyleContext.cpp
+++ b/layout/style/nsStyleContext.cpp
@@ -51,6 +51,7 @@
 #include "nsRuleNode.h"
 #include "nsStyleContext.h"
 #include "prlog.h"
+#include "nsStyleAnimation.h"
 
 #ifdef DEBUG
 // #define NOISY_DEBUG
@@ -685,3 +686,57 @@ NS_NewStyleContext(nsStyleContext* aParentContext,
   return context;
 }
 
+static nscolor ExtractColor(nsCSSProperty aProperty,
+                            nsStyleContext *aStyleContext)
+{
+  nsStyleAnimation::Value val;
+#ifdef DEBUG
+  PRBool success =
+#endif
+    nsStyleAnimation::ExtractComputedValue(aProperty, aStyleContext, val);
+  NS_ABORT_IF_FALSE(success,
+                    "aProperty must be extractable by nsStyleAnimation");
+  return val.GetColorValue();
+}
+
+struct ColorIndexSet {
+  PRUint8 colorIndex, alphaIndex;
+};
+
+static const ColorIndexSet gVisitedIndices[2] = { { 0, 0 }, { 1, 0 } };
+
+nscolor
+nsStyleContext::GetVisitedDependentColor(nsCSSProperty aProperty)
+{
+  NS_ASSERTION(aProperty == eCSSProperty_color ||
+               aProperty == eCSSProperty_background_color ||
+               aProperty == eCSSProperty_border_top_color ||
+               aProperty == eCSSProperty_border_right_color_value ||
+               aProperty == eCSSProperty_border_bottom_color ||
+               aProperty == eCSSProperty_border_left_color_value ||
+               aProperty == eCSSProperty_outline_color ||
+               aProperty == eCSSProperty__moz_column_rule_color ||
+               aProperty == eCSSProperty_fill ||
+               aProperty == eCSSProperty_stroke,
+               "we need to add to nsStyleContext::CalcStyleDifference");
+
+  nscolor colors[2];
+  colors[0] = ExtractColor(aProperty, this);
+
+  nsStyleContext *visitedStyle = this->GetStyleIfVisited();
+  if (!visitedStyle) {
+    return colors[0];
+  }
+
+  colors[1] = ExtractColor(aProperty, visitedStyle);
+
+  // NOTE: We want this code to have as little timing dependence as
+  // possible on whether this->RelevantLinkVisited() is true.
+  const ColorIndexSet &set =
+    gVisitedIndices[this->RelevantLinkVisited() ? 1 : 0];
+
+  nscolor colorColor = colors[set.colorIndex];
+  nscolor alphaColor = colors[set.alphaIndex];
+  return NS_RGBA(NS_GET_R(colorColor), NS_GET_G(colorColor),
+                 NS_GET_B(colorColor), NS_GET_A(alphaColor));
+}
diff --git a/layout/style/nsStyleContext.h b/layout/style/nsStyleContext.h
index 778df6ab2dd..8bddf174f49 100644
--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -248,6 +248,16 @@ public:
 
   NS_HIDDEN_(nsChangeHint) CalcStyleDifference(nsStyleContext* aOther);
 
+  /**
+   * Get a color that depends on link-visitedness using this and
+   * this->GetStyleIfVisited().
+   *
+   * aProperty must be a color-valued property that nsStyleAnimation
+   * knows how to extract.  It must also be a property that we know to
+   * do change handling for in nsStyleContext::CalcDifference.
+   */
+  NS_HIDDEN_(nscolor) GetVisitedDependentColor(nsCSSProperty aProperty);
+
 #ifdef DEBUG
   NS_HIDDEN_(void) List(FILE* out, PRInt32 aIndent);
 #endif