Proper support for multiple text decorations.

Source/core/rendering/style/RenderStyle.cpp

Index: Source/core/rendering/style/RenderStyle.cpp
diff --git a/Source/core/rendering/style/RenderStyle.cpp b/Source/core/rendering/style/RenderStyle.cpp
index dfeb3bed61f5b2ce8ec111e0e8193140b5c768cd..4d5b9103b04bd38bd768524e813771eef50650f1 100644
--- a/Source/core/rendering/style/RenderStyle.cpp
+++ b/Source/core/rendering/style/RenderStyle.cpp
@@ -28,6 +28,7 @@
 #include "core/css/resolver/StyleResolver.h"
 #include "core/rendering/RenderTheme.h"
 #include "core/rendering/TextAutosizer.h"
+#include "core/rendering/style/AppliedTextDecoration.h"
 #include "core/rendering/style/ContentData.h"
 #include "core/rendering/style/CursorList.h"
 #include "core/rendering/style/QuotesData.h"
@@ -688,7 +689,7 @@ unsigned RenderStyle::computeChangedContextSensitiveProperties(const RenderStyle
 
     if (!diff.needsRepaint()) {
         if (inherited->color != other.inherited->color
-            || inherited_flags._text_decorations != other.inherited_flags._text_decorations
+            || inherited_flags.m_textUnderline != other.inherited_flags.m_textUnderline
             || visual->textDecoration != other.visual->textDecoration) {
             changedContextSensitiveProperties |= ContextSensitivePropertyTextOrColor;
         } else if (rareNonInheritedData.get() != other.rareNonInheritedData.get()) {
@@ -699,7 +700,8 @@ unsigned RenderStyle::computeChangedContextSensitiveProperties(const RenderStyle
             if (rareInheritedData->textFillColor() != other.rareInheritedData->textFillColor()
                 || rareInheritedData->textStrokeColor() != other.rareInheritedData->textStrokeColor()
                 || rareInheritedData->textEmphasisColor() != other.rareInheritedData->textEmphasisColor()
-                || rareInheritedData->textEmphasisFill != other.rareInheritedData->textEmphasisFill)
+                || rareInheritedData->textEmphasisFill != other.rareInheritedData->textEmphasisFill
+                || rareInheritedData->appliedTextDecorations != other.rareInheritedData->appliedTextDecorations)
                 changedContextSensitiveProperties |= ContextSensitivePropertyTextOrColor;
         }
     }
@@ -1204,6 +1206,31 @@ float RenderStyle::computedFontSize() const { return fontDescription().computedS
 int RenderStyle::fontSize() const { return fontDescription().computedPixelSize(); }
 FontWeight RenderStyle::fontWeight() const { return fontDescription().weight(); }
 
+TextDecoration RenderStyle::textDecorationsInEffect() const
+{
+    int decorations = 0;
+
+    const Vector<AppliedTextDecoration>& applied = appliedTextDecorations();
+
+    for (size_t i = 0; i < applied.size(); ++i)
+        decorations |= applied[i].line();
+
+    return static_cast<TextDecoration>(decorations);
+}
+
+const Vector<AppliedTextDecoration>& RenderStyle::appliedTextDecorations() const
+{
+    DEFINE_STATIC_LOCAL(Vector<AppliedTextDecoration>, empty, ());
+    DEFINE_STATIC_LOCAL(Vector<AppliedTextDecoration>, underline, (1, AppliedTextDecoration(TextDecorationUnderline)));

[Julien - ping for review, 2014/05/05 17:45:08]

I would prefer the vectors to be defined inside their own branches. This matches
our coding style to define local variable the closest / deepest to where they
are needed.

[andersr, 2014/05/06 13:15:29]

Done.

+
+    if (!inherited_flags.m_textUnderline && !rareInheritedData->appliedTextDecorations)

[Julien - ping for review, 2014/05/05 17:45:08]

This line makes me think that when inherited_flags.m_textUnderline is false,
rareInheritedData->appliedTextDecorations shouldn't be NULL.

[andersr, 2014/05/06 13:15:29]

Do you mean that it does not read well, or that it's logically wrong? (It looks
correct to me). What would you prefer?

!(m_textUnderline || appliedTextDecoration) // This?

+        return empty;
+    if (inherited_flags.m_textUnderline && !rareInheritedData->appliedTextDecorations)

[Julien - ping for review, 2014/05/05 17:45:08]

Wouldn't rareInheritedData->appliedTextDecorations be NULL if
inherited_flags.m_textUnderline is true based on the addAppliedTextDecoration
logic below?

[andersr, 2014/05/06 13:15:29]

That's true. Fixed.

+        return underline;
+
+    return rareInheritedData->appliedTextDecorations->vector();
+}
+
 float RenderStyle::wordSpacing() const { return fontDescription().wordSpacing(); }
 float RenderStyle::letterSpacing() const { return fontDescription().letterSpacing(); }
 
@@ -1299,6 +1326,72 @@ void RenderStyle::setFontWeight(FontWeight weight)
     font().update(currentFontSelector);
 }
 
+void RenderStyle::setTextDecorationsInEffect(TextDecoration decorations)
+{
+    clearAppliedTextDecorations();
+
+    if (decorations & TextDecorationUnderline)
+        addAppliedTextDecoration(AppliedTextDecoration(TextDecorationUnderline));
+    if (decorations & TextDecorationOverline)
+        addAppliedTextDecoration(AppliedTextDecoration(TextDecorationOverline));
+    if (decorations & TextDecorationLineThrough)
+        addAppliedTextDecoration(AppliedTextDecoration(TextDecorationLineThrough));
+}
+
+void RenderStyle::addAppliedTextDecoration(const AppliedTextDecoration& decoration)
+{
+    bool isSimpleUnderline = decoration.isSimple() && decoration.line() == TextDecorationUnderline;

[Julien - ping for review, 2014/05/05 17:45:08]

It's weird that we check for this simple case repeatedly here when the caller
knows all the text-decorations that applies to an element so could easily set
the flag and insert the extra AppliedTextDecoration as needed.

[andersr, 2014/05/06 13:15:29]

I don't know ... is that really weird?

Currently, addAppliedTextDecoration "packs" the simple decoration into a single
bit, and the appliedTextDecorations "unpacks" the simple decoration, as
appropriate. It seems natural to me that this optimization should be an
implementation detail of the setter/getter, and not something utility functions
(applyTextDecorations) and/or callers need to even know about.

+
+    if (!rareInheritedData->appliedTextDecorations && isSimpleUnderline) {
+        // To save memory, we don't use AppliedTextDecoration objects in the
+        // common case of a single solid underline with the current color. Instead,
+        // we set a bit to indicate that a solid underline must be drawn with the
+        // current color.
+        inherited_flags.m_textUnderline = true;
+        return;
+    }
+
+    RefPtr<AppliedTextDecorationList>& list = rareInheritedData.access()->appliedTextDecorations;
+
+    if (!list)
+        list = AppliedTextDecorationList::create();
+    else if (!list->hasOneRef())
+        list = list->copy();

[Julien - ping for review, 2014/05/05 17:45:08]

It's probably me but I have a hard time understanding:
A) Why we need this copy?
B) Why we need such a complex sharing code for a rare property and a Vector that
holds at most 4 elements?

[andersr, 2014/05/06 13:15:29]

A) The same reason we copy DataRef objects? When the applied decorations of a
child changes, it should not apply to the parent. I realize this behavior is
almost identical to DataRef (the difference is that DataRefs must always be
initialized, which we don't want), however, there is already a precedent in
RenderStyle to do it this way in such situations. (CursorList).

I could submit a follow up patch with optional lazy initialization for DataRef.
(Or something like that).

B) How did you arrive at the number '4'? I believe it can hold up to [number of
lines] * [number of styles] effective elements, which currently computes to
'15'.

Example: For each [underline, line-through, overline], you can draw (in order):
[wavy, double, solid, dashed, dotted], and portions of all those decorations
will be visible. Beyond that, I believe some decorations *could* be dropped,
yes, but it makes no sense to optimize such cases.

+
+    if (inherited_flags.m_textUnderline) {
+        inherited_flags.m_textUnderline = false;
+        list->append(AppliedTextDecoration(TextDecorationUnderline, TextDecorationStyleSolid, StyleColor::currentColor()));
+    }
+
+    list->append(decoration);
+}
+
+void RenderStyle::applyTextDecorations()
+{
+    if (textDecoration() == TextDecorationNone)
+        return;
+
+    TextDecorationStyle style = textDecorationStyle();
+    StyleColor styleColor = visitedDependentDecorationStyleColor();
+
+    int decorations = textDecoration();
+
+    if (decorations & TextDecorationUnderline)
+        addAppliedTextDecoration(AppliedTextDecoration(TextDecorationUnderline, style, styleColor));
+    if (decorations & TextDecorationOverline)
+        addAppliedTextDecoration(AppliedTextDecoration(TextDecorationOverline, style, styleColor));
+    if (decorations & TextDecorationLineThrough)
+        addAppliedTextDecoration(AppliedTextDecoration(TextDecorationLineThrough, style, styleColor));
+}
+
+void RenderStyle::clearAppliedTextDecorations()
+{
+    inherited_flags.m_textUnderline = false;
+
+    if (rareInheritedData->appliedTextDecorations)
+        rareInheritedData.access()->appliedTextDecorations = nullptr;
+}
+
 void RenderStyle::getShadowExtent(const ShadowList* shadowList, LayoutUnit &top, LayoutUnit &right, LayoutUnit &bottom, LayoutUnit &left) const
 {
     top = 0;
@@ -1376,10 +1469,29 @@ void RenderStyle::getShadowVerticalExtent(const ShadowList* shadowList, LayoutUn
     }
 }
 
-StyleColor RenderStyle::visitedDependentDecorationColor() const
+StyleColor RenderStyle::visitedDependentDecorationStyleColor() const
+{
+    bool visitedLink = insideLink() == InsideVisitedLink;
+
+    StyleColor styleColor = visitedLink ? visitedLinkTextDecorationColor() : textDecorationColor();
+
+    if (!styleColor.isCurrentColor())
+        return styleColor;
+
+    if (textStrokeWidth()) {
+        // Prefer stroke color if possible but not if it's fully transparent.
+        StyleColor textStrokeStyleColor = visitedLink ? visitedLinkTextStrokeColor() : textStrokeColor();
+        if (!textStrokeStyleColor.isCurrentColor() && textStrokeStyleColor.color().alpha())
+            return textStrokeStyleColor;
+    }
+
+    return visitedLink ? visitedLinkTextFillColor() : textFillColor();
+}
+
+Color RenderStyle::visitedDependentDecorationColor() const
 {
-    // Text decoration color fallback is handled in RenderObject::decorationColor.
-    return insideLink() == InsideVisitedLink ? visitedLinkTextDecorationColor() : textDecorationColor();
+    bool visitedLink = insideLink() == InsideVisitedLink;
+    return visitedDependentDecorationStyleColor().resolve(visitedLink ? visitedLinkColor() : color());
 }
 
 Color RenderStyle::colorIncludingFallback(int colorProperty, bool visitedLink) const