Bug 901845 - add a pref to specify the length limit of words in word caches. r=jfkthame

gfx/thebes/gfxFont.cpp

@@ -3242,6 +3242,8 @@ gfxFont::SplitAndInitTextRun(gfxContext *aContext,
     }
 
     InitWordCache();
+    uint32_t wordCacheCharLimit =
+        gfxPlatform::GetPlatform()->WordCacheCharLimit();
 
     // the only flags we care about for ShapedWord construction/caching
     uint32_t flags = aTextRun->GetFlags();
@@ -3279,9 +3281,9 @@ gfxFont::SplitAndInitTextRun(gfxContext *aContext,
 
         // We've decided to break here (i.e. we're at the end of a "word");
         // shape the word and add it to the textrun.
-        // For words longer than gfxShapedWord::kMaxLength, we don't use the
+        // For words longer than the limit, we don't use the
         // font's word cache but just shape directly into the textrun.
-        if (length > gfxShapedWord::kMaxLength) {
+        if (length > wordCacheCharLimit) {
             bool ok = ShapeFragmentWithoutWordCache(aContext,
                                                     text + wordStart,
                                                     aRunStart + wordStart,

gfx/thebes/gfxFont.h

@@ -2467,8 +2467,6 @@ protected:
 class gfxShapedWord : public gfxShapedText
 {
 public:
-    static const uint32_t kMaxLength = 32;
-
     // Create a ShapedWord that can hold glyphs for aLength characters,
     // with mCharacterGlyphs sized appropriately.
     //
@@ -2482,7 +2480,8 @@ public:
                                  int32_t aRunScript,
                                  int32_t aAppUnitsPerDevUnit,
                                  uint32_t aFlags) {
-        NS_ASSERTION(aLength <= kMaxLength, "excessive length for gfxShapedWord!");
+        NS_ASSERTION(aLength <= gfxPlatform::GetPlatform()->WordCacheCharLimit(),
+                     "excessive length for gfxShapedWord!");
 
         // Compute size needed including the mCharacterGlyphs array
         // and a copy of the original text
@@ -2503,7 +2502,8 @@ public:
                                  int32_t aRunScript,
                                  int32_t aAppUnitsPerDevUnit,
                                  uint32_t aFlags) {
-        NS_ASSERTION(aLength <= kMaxLength, "excessive length for gfxShapedWord!");
+        NS_ASSERTION(aLength <= gfxPlatform::GetPlatform()->WordCacheCharLimit(),
+                     "excessive length for gfxShapedWord!");
 
         // In the 16-bit version of Create, if the TEXT_IS_8BIT flag is set,
         // then we convert the text to an 8-bit version and call the 8-bit

gfx/thebes/gfxPlatform.cpp

@@ -150,6 +150,8 @@ SRGBOverrideObserver::Observe(nsISupports *aSubject,
 
 #define GFX_PREF_OPENTYPE_SVG "gfx.font_rendering.opentype_svg.enabled"
 
+#define GFX_PREF_WORD_CACHE_CHARLIMIT "gfx.font_rendering.wordcache.charlimit"
+
 #define GFX_PREF_GRAPHITE_SHAPING "gfx.font_rendering.graphite.enabled"
 
 #define BIDI_NUMERAL_PREF "bidi.numeral"
@@ -257,6 +259,7 @@ gfxPlatform::gfxPlatform()
     mAllowDownloadableFonts = UNINITIALIZED_VALUE;
     mFallbackUsesCmaps = UNINITIALIZED_VALUE;
 
+    mWordCacheCharLimit = UNINITIALIZED_VALUE;
     mGraphiteShapingEnabled = UNINITIALIZED_VALUE;
     mOpenTypeSVGEnabled = UNINITIALIZED_VALUE;
     mBidiNumeralOption = UNINITIALIZED_VALUE;
@@ -963,6 +966,20 @@ gfxPlatform::OpenTypeSVGEnabled()
     return mOpenTypeSVGEnabled > 0;
 }
 
+uint32_t
+gfxPlatform::WordCacheCharLimit()
+{
+    if (mWordCacheCharLimit == UNINITIALIZED_VALUE) {
+        mWordCacheCharLimit =
+            Preferences::GetInt(GFX_PREF_WORD_CACHE_CHARLIMIT, 32);
+        if (mWordCacheCharLimit < 0) {
+            mWordCacheCharLimit = 32;
+        }
+    }
+
+    return uint32_t(mWordCacheCharLimit);
+}
+
 bool
 gfxPlatform::UseGraphiteShaping()
 {
@@ -1770,6 +1787,13 @@ gfxPlatform::FontsPrefsChanged(const char *aPref)
         mAllowDownloadableFonts = UNINITIALIZED_VALUE;
     } else if (!strcmp(GFX_PREF_FALLBACK_USE_CMAPS, aPref)) {
         mFallbackUsesCmaps = UNINITIALIZED_VALUE;
+    } else if (!strcmp(GFX_PREF_WORD_CACHE_CHARLIMIT, aPref)) {
+        mWordCacheCharLimit = UNINITIALIZED_VALUE;
+        gfxFontCache *fontCache = gfxFontCache::GetCache();
+        if (fontCache) {
+            fontCache->AgeAllGenerations();
+            fontCache->FlushShapedWordCaches();
+        }
     } else if (!strcmp(GFX_PREF_GRAPHITE_SHAPING, aPref)) {
         mGraphiteShapingEnabled = UNINITIALIZED_VALUE;
         gfxFontCache *fontCache = gfxFontCache::GetCache();

gfx/thebes/gfxPlatform.h

@@ -403,6 +403,11 @@ public:
      */
     bool OpenTypeSVGEnabled();
 
+    /**
+     * Max character length of words in the word cache
+     */
+    uint32_t WordCacheCharLimit();
+
     /**
      * Whether to use the SIL Graphite rendering engine
      * (for fonts that include Graphite tables)
@@ -672,6 +677,9 @@ protected:
     // which scripts should be shaped with harfbuzz
     int32_t mUseHarfBuzzScripts;
 
+    // max character limit for words in word cache
+    int32_t mWordCacheCharLimit;
+
 private:
     /**
      * Start up Thebes.

modules/libpref/src/init/all.js

@@ -292,6 +292,9 @@ pref("gfx.font_loader.interval", 50);          // run every 50 ms
 // whether to always search all font cmaps during system font fallback
 pref("gfx.font_rendering.fallback.always_use_cmaps", false);
 
+// cache shaped word results
+pref("gfx.font_rendering.wordcache.charlimit", 32);
+
 pref("gfx.font_rendering.graphite.enabled", true);
 
 // Check intl/unicharutil/util/nsUnicodeProperties.h for definitions of script bits