Bug 705594. Add pref to force global cmap-based font fallback. r=roc

gfx/thebes/gfxPlatform.cpp

@@ -150,6 +150,7 @@ SRGBOverrideObserver::Observe(nsISupports *aSubject,
 
 #define GFX_PREF_HARFBUZZ_SCRIPTS "gfx.font_rendering.harfbuzz.scripts"
 #define HARFBUZZ_SCRIPTS_DEFAULT  mozilla::unicode::SHAPING_DEFAULT
+#define GFX_PREF_FALLBACK_USE_CMAPS  "gfx.font_rendering.fallback.always_use_cmaps"
 
 #ifdef MOZ_GRAPHITE
 #define GFX_PREF_GRAPHITE_SHAPING "gfx.font_rendering.graphite.enabled"
@@ -233,6 +234,8 @@ gfxPlatform::gfxPlatform()
     mUseHarfBuzzScripts = UNINITIALIZED_VALUE;
     mAllowDownloadableFonts = UNINITIALIZED_VALUE;
     mDownloadableFontsSanitize = UNINITIALIZED_VALUE;
+    mFallbackUsesCmaps = UNINITIALIZED_VALUE;
+
 #ifdef MOZ_GRAPHITE
     mGraphiteShapingEnabled = UNINITIALIZED_VALUE;
 #endif
@@ -682,6 +685,17 @@ gfxPlatform::SanitizeDownloadedFonts()
     return mDownloadableFontsSanitize;
 }
 
+bool
+gfxPlatform::UseCmapsDuringSystemFallback()
+{
+    if (mFallbackUsesCmaps == UNINITIALIZED_VALUE) {
+        mFallbackUsesCmaps =
+            Preferences::GetBool(GFX_PREF_FALLBACK_USE_CMAPS, false);
+    }
+
+    return mFallbackUsesCmaps;
+}
+
 #ifdef MOZ_GRAPHITE
 bool
 gfxPlatform::UseGraphiteShaping()
@@ -1360,6 +1374,8 @@ gfxPlatform::FontsPrefsChanged(const char *aPref)
         mAllowDownloadableFonts = UNINITIALIZED_VALUE;
     } else if (!strcmp(GFX_DOWNLOADABLE_FONTS_SANITIZE, aPref)) {
         mDownloadableFontsSanitize = UNINITIALIZED_VALUE;
+    } else if (!strcmp(GFX_PREF_FALLBACK_USE_CMAPS, aPref)) {
+        mFallbackUsesCmaps = UNINITIALIZED_VALUE;
 #ifdef MOZ_GRAPHITE
     } else if (!strcmp(GFX_PREF_GRAPHITE_SHAPING, aPref)) {
         mGraphiteShapingEnabled = UNINITIALIZED_VALUE;

gfx/thebes/gfxPlatform.h

@@ -319,6 +319,11 @@ public:
      */
     virtual bool FontHintingEnabled() { return true; }
 
+    /**
+     * Whether to check all font cmaps during system font fallback
+     */
+    bool UseCmapsDuringSystemFallback();
+
 #ifdef MOZ_GRAPHITE
     /**
      * Whether to use the SIL Graphite rendering engine
@@ -465,6 +470,10 @@ protected:
 
     PRInt8  mBidiNumeralOption;
 
+    // whether to always search font cmaps globally 
+    // when doing system font fallback
+    PRInt8  mFallbackUsesCmaps;
+
     // which scripts should be shaped with harfbuzz
     PRInt32 mUseHarfBuzzScripts;
 

gfx/thebes/gfxPlatformFontList.cpp

@@ -666,10 +666,12 @@ gfxPlatformFontList::InitLoader()
     mNumFamilies = mFontFamiliesToLoad.Length();
 }
 
-bool 
+bool
 gfxPlatformFontList::RunLoader()
 {
     PRUint32 i, endIndex = (mStartIndex + mIncrement < mNumFamilies ? mStartIndex + mIncrement : mNumFamilies);
+    bool loadCmaps = !UsesSystemFallback() ||
+        gfxPlatform::GetPlatform()->UseCmapsDuringSystemFallback();
 
     // for each font family, load in various font info
     for (i = mStartIndex; i < endIndex; i++) {
@@ -685,8 +687,10 @@ gfxPlatformFontList::RunLoader()
             continue;
         }
 
-        // load the cmaps
-        familyEntry->ReadAllCMAPs();
+        // load the cmaps if needed
+        if (loadCmaps) {
+            familyEntry->ReadAllCMAPs();
+        }
 
         // read in face names
         familyEntry->ReadFaceNames(this, mNeedFullnamePostscriptNames);

gfx/thebes/gfxPlatformFontList.h

@@ -161,6 +161,10 @@ protected:
                                              const gfxFontStyle* aMatchStyle,
                                              PRUint32& aCmapCount);
 
+    // whether system-based font fallback is used or not
+    // if system fallback is used, no need to load all cmaps
+    virtual bool UsesSystemFallback() { return false; }
+
     // separate initialization for reading in name tables, since this is expensive
     void InitOtherFamilyNames();
 

modules/libpref/src/init/all.js

@@ -203,6 +203,9 @@ pref("gfx.downloadable_fonts.enabled", true);
 pref("gfx.downloadable_fonts.fallback_delay", 3000);
 pref("gfx.downloadable_fonts.sanitize", true);
 
+// whether to always search all font cmaps during system font fallback
+pref("gfx.font_rendering.fallback.always_use_cmaps", false);
+
 #ifdef MOZ_GRAPHITE
 pref("gfx.font_rendering.graphite.enabled", false);
 #endif