Bug 549861. Trim out kerning from gfxFontStyle. r=jkew

gfx/src/nsFont.cpp

@@ -302,12 +302,10 @@ void nsFont::AddFontFeaturesToStyle(gfxFontStyle *aStyle) const
   switch (kerning) {
     case NS_FONT_KERNING_NONE:
       setting.mValue = 0;
-      aStyle->kerning = false;
       aStyle->featureSettings.AppendElement(setting);
       break;
     case NS_FONT_KERNING_NORMAL:
       setting.mValue = 1;
-      aStyle->kerning = true;
       aStyle->featureSettings.AppendElement(setting);
       break;
     default:

gfx/thebes/gfxFont.cpp

@@ -4865,7 +4865,7 @@ gfxFontStyle::gfxFontStyle() :
     languageOverride(NO_FONT_LANGUAGE_OVERRIDE),
     weight(NS_FONT_WEIGHT_NORMAL), stretch(NS_FONT_STRETCH_NORMAL),
     systemFont(true), printerFont(false), 
-    kerning(true), style(NS_FONT_STYLE_NORMAL)
+    style(NS_FONT_STYLE_NORMAL)
 {
 }
 
@@ -4879,7 +4879,7 @@ gfxFontStyle::gfxFontStyle(uint8_t aStyle, uint16_t aWeight, int16_t aStretch,
     languageOverride(ParseFontLanguageOverride(aLanguageOverride)),
     weight(aWeight), stretch(aStretch),
     systemFont(aSystemFont), printerFont(aPrinterFont),
-    kerning(true), style(aStyle)
+    style(aStyle)
 {
     MOZ_ASSERT(!mozilla::IsNaN(size));
     MOZ_ASSERT(!mozilla::IsNaN(sizeAdjust));
@@ -4910,7 +4910,7 @@ gfxFontStyle::gfxFontStyle(const gfxFontStyle& aStyle) :
     languageOverride(aStyle.languageOverride),
     weight(aStyle.weight), stretch(aStyle.stretch),
     systemFont(aStyle.systemFont), printerFont(aStyle.printerFont),
-    kerning(aStyle.kerning), style(aStyle.style)
+    style(aStyle.style)
 {
     featureSettings.AppendElements(aStyle.featureSettings);
     alternateValues.AppendElements(aStyle.alternateValues);

gfx/thebes/gfxFont.h

@@ -126,9 +126,6 @@ struct THEBES_API gfxFontStyle {
     // Say that this font is used for print or print preview.
     bool printerFont : 1;
 
-    // whether kerning is enabled or not (true by default, can be disabled)
-    bool kerning : 1;
-
     // The style of font (normal, italic, oblique)
     uint8_t style : 2;
 
@@ -160,7 +157,6 @@ struct THEBES_API gfxFontStyle {
             (language == other.language) &&
             (*reinterpret_cast<const uint32_t*>(&sizeAdjust) ==
              *reinterpret_cast<const uint32_t*>(&other.sizeAdjust)) &&
-            (kerning == other.kerning) &&
             (featureSettings == other.featureSettings) &&
             (languageOverride == other.languageOverride) &&
             (alternateValues == other.alternateValues) &&
@@ -1601,6 +1597,10 @@ public:
     virtual mozilla::TemporaryRef<mozilla::gfx::ScaledFont> GetScaledFont(mozilla::gfx::DrawTarget *aTarget)
     { return gfxPlatform::GetPlatform()->GetScaledFontForFont(aTarget, this); }
 
+    bool KerningDisabled() {
+        return mKerningSet && !mKerningEnabled;
+    }
+
 protected:
 
     bool HasSubstitutionRulesWithSpaceLookups(int32_t aRunScript) {

gfx/thebes/gfxHarfBuzzShaper.cpp

@@ -965,7 +965,8 @@ gfxHarfBuzzShaper::ShapeText(gfxContext      *aContext,
     }
 
     const gfxFontStyle *style = mFont->GetStyle();
-    FontCallbackData fcd(this, aContext, style->kerning);
+    // kerning is enabled *except* when explicitly disabled (font-kerning: none)
+    FontCallbackData fcd(this, aContext, !mFont->KerningDisabled());
     hb_font_t *font = hb_font_create(mHBFace);
     hb_font_set_funcs(font, sHBFontFuncs, &fcd, nullptr);
     hb_font_set_ppem(font, mFont->GetAdjustedSize(), mFont->GetAdjustedSize());