Bug 380484. Work around ATSUI's 32k pixel limitation; when creating textruns, split the textrun up into smaller pieces if necessary before we pass it to ATSUI. r=vlad

gfx/thebes/public/gfxAtsuiFonts.h

@@ -128,8 +128,11 @@ protected:
                                const nsACString& aGenericName,
                                void *closure);
 
-    void InitTextRun(gfxTextRun *aRun, const PRUnichar *aString, PRUint32 aLength,
-                     PRBool aWrapped);
+    PRUint32 GuessMaximumStringLength();
+
+    /** Returns true for success */
+    PRBool InitTextRun(gfxTextRun *aRun, const PRUnichar *aString, PRUint32 aLength,
+                       PRBool aWrapped, PRUint32 aSegmentStart, PRUint32 aSegmentLength);
 
     ATSUFontFallbacks mFallbacks;
 };

gfx/thebes/src/gfxAtsuiFonts.cpp

@@ -422,21 +422,6 @@ SetupClusterBoundaries(gfxTextRun *aTextRun, const PRUnichar *aString)
     UCDisposeTextBreakLocator(&locator);
 }
 
-void
-gfxAtsuiFontGroup::MakeTextRunInternal(const PRUnichar *aString, PRUint32 aLength,
-                                       PRBool aWrapped, gfxTextRun *aTextRun)
-{
-    // NS_ASSERTION(!(aParams->mFlags & TEXT_NEED_BOUNDING_BOX),
-    //              "Glyph extents not yet supported");
-    const PRUnichar *realString = aString + (aWrapped ? 1 : 0);
-    aTextRun->RecordSurrogates(realString);
-    if (!(aTextRun->GetFlags() & TEXT_IS_8BIT)) {
-        SetupClusterBoundaries(aTextRun, realString);
-    }
-
-    InitTextRun(aTextRun, aString, aLength, aWrapped);
-}
-
 #define UNICODE_LRO 0x202d
 #define UNICODE_RLO 0x202e
 #define UNICODE_PDF 0x202c
@@ -448,6 +433,70 @@ AppendDirectionalIndicator(PRUint32 aFlags, nsAString& aString)
     aString.Append(overrides[(aFlags & gfxTextRunFactory::TEXT_IS_RTL) != 0]);
 }
 
+/**
+ * Given a textrun and an offset into that textrun, we need to choose a length
+ * for the substring of the textrun that we should analyze next. The length
+ * should be <= aMaxLength if possible. It must always end at a cluster
+ * boundary and it should end at the end of the textrun or at the
+ * boundary of a space if possible.
+ */
+static PRUint32
+FindTextRunSegmentLength(gfxTextRun *aTextRun, PRUint32 aOffset, PRUint32 aMaxLength)
+{
+    if (aOffset + aMaxLength >= aTextRun->GetLength()) {
+        // The remaining part of the textrun fits within the max length,
+        // so just use it.
+        return aTextRun->GetLength() - aOffset;
+    }
+
+    // Try to end the segment before or after a space, since spaces don't kern
+    // or ligate.
+    PRUint32 end;
+    for (end = aOffset + aMaxLength; end > aOffset; --end) {
+        if (aTextRun->IsClusterStart(end) &&
+            (aTextRun->GetChar(end) == ' ' || aTextRun->GetChar(end - 1) == ' '))
+            return end - aOffset;
+    }
+
+    // Try to end the segment at the last cluster boundary.
+    for (end = aOffset + aMaxLength; end > aOffset; --end) {
+        if (aTextRun->IsClusterStart(end))
+            return end - aOffset;
+    }
+
+    // I guess we just have to return a segment that's the entire cluster
+    // starting at aOffset.
+    for (end = aOffset + 1; end < aTextRun->GetLength(); ++end) {
+        if (aTextRun->IsClusterStart(end))
+            return end - aOffset;
+    }
+    return aTextRun->GetLength() - aOffset;
+}
+
+PRUint32
+gfxAtsuiFontGroup::GuessMaximumStringLength()
+{
+    gfxFloat maxAdvance = GetFontAt(0)->GetMetrics().maxAdvance;
+    // ATSUI can't handle offsets of more than 32K pixels
+    PRUint32 chars = 0x7FFF/PRUint32(maxAdvance);
+    return PR_MAX(1, chars);
+}
+
+/*
+ * ATSUI can't handle more than 32K pixels of text. We can easily have
+ * textruns longer than that. Our strategy here is to divide the textrun up
+ * into pieces each of which is less than 32K pixels wide. We pick a number
+ * of characters 'maxLen' such that the first font's max-advance times that
+ * number of characters is less than 32K pixels; then we try glyph conversion
+ * of the string broken up into chunks each with no more than 'maxLen'
+ * characters. That could fail (e.g. if fallback fonts are used); if it does,
+ * we retry with a smaller maxLen. When breaking up the string into chunks
+ * we prefer to break at space boundaries because spaces don't kern or ligate
+ * with other characters, usually. We insist on breaking at cluster boundaries.
+ * If the font size is incredibly huge and/or clusters are very large, this
+ * could mean that we actually put more than 'maxLen' characters in a chunk.
+ */
+
 gfxTextRun *
 gfxAtsuiFontGroup::MakeTextRun(const PRUnichar *aString, PRUint32 aLength,
                                const Parameters *aParams, PRUint32 aFlags)
@@ -456,14 +505,33 @@ gfxAtsuiFontGroup::MakeTextRun(const PRUnichar *aString, PRUint32 aLength,
     if (!textRun)
         return nsnull;
 
+    textRun->RecordSurrogates(aString);
+    SetupClusterBoundaries(textRun, aString);
+
+    PRUint32 maxLen;
     nsAutoString utf16;
-    AppendDirectionalIndicator(aFlags, utf16);
-    utf16.Append(aString, aLength);
-    // Ensure that none of the whitespace in the run is considered "trailing"
-    // by ATSUI's bidi algorithm
-    utf16.Append('.');
-    utf16.Append(UNICODE_PDF);
-    MakeTextRunInternal(utf16.get(), utf16.Length(), PR_TRUE, textRun);
+    for (maxLen = GuessMaximumStringLength(); maxLen > 0; maxLen /= 2) {
+        PRUint32 start = 0;
+        while (start < aLength) {
+            PRUint32 len = FindTextRunSegmentLength(textRun, start, maxLen);
+
+            utf16.Truncate();
+            AppendDirectionalIndicator(aFlags, utf16);
+            utf16.Append(aString + start, len);
+            // Ensure that none of the whitespace in the run is considered "trailing"
+            // by ATSUI's bidi algorithm
+            utf16.Append('.');
+            utf16.Append(UNICODE_PDF);
+            if (!InitTextRun(textRun, utf16.get(), utf16.Length(), PR_TRUE,
+                             start, len) && maxLen > 1)
+                break;
+            start += len;
+        }
+        if (start == aLength)
+            break;
+        textRun->ResetGlyphRuns();
+    }
+
     return textRun;
 }
 
@@ -476,19 +544,35 @@ gfxAtsuiFontGroup::MakeTextRun(const PRUint8 *aString, PRUint32 aLength,
     if (!textRun)
         return nsnull;
 
-    nsDependentCSubstring cString(reinterpret_cast<const char*>(aString),
-                                  reinterpret_cast<const char*>(aString + aLength));
+    PRUint32 maxLen;
     nsAutoString utf16;
-    PRBool wrapBidi = (aFlags & TEXT_IS_RTL) != 0;
-    if (wrapBidi) {
-      AppendDirectionalIndicator(aFlags, utf16);
+    for (maxLen = GuessMaximumStringLength(); maxLen > 0; maxLen /= 2) {
+        PRUint32 start = 0;
+        while (start < aLength) {
+            PRUint32 len = FindTextRunSegmentLength(textRun, start, maxLen);
+
+            nsDependentCSubstring cString(reinterpret_cast<const char*>(aString + start),
+                                          reinterpret_cast<const char*>(aString + start + len));
+            utf16.Truncate();
+            PRBool wrapBidi = (aFlags & TEXT_IS_RTL) != 0;
+            if (wrapBidi) {
+              AppendDirectionalIndicator(aFlags, utf16);
+            }
+            AppendASCIItoUTF16(cString, utf16);
+            if (wrapBidi) {
+              utf16.Append('.');
+              utf16.Append(UNICODE_PDF);
+            }
+            if (!InitTextRun(textRun, utf16.get(), utf16.Length(), wrapBidi,
+                             start, len) && maxLen > 1)
+                break;
+            start += len;
+        }
+        if (start == aLength)
+            break;
+        textRun->ResetGlyphRuns();
     }
-    AppendASCIItoUTF16(cString, utf16);
-    if (wrapBidi) {
-      utf16.Append('.');
-      utf16.Append(UNICODE_PDF);
-    }
-    MakeTextRunInternal(utf16.get(), utf16.Length(), wrapBidi, textRun);
+
     return textRun;
 }
 
@@ -540,7 +624,12 @@ private:
     ATSUDirectDataSelector mSelector;
 };
 
-#define ATSUI_SPECIAL_GLYPH_ID 0xFFFF
+#define ATSUI_SPECIAL_GLYPH_ID       0xFFFF
+/**
+ * This flag seems to be set on glyphs that have overrun the 32K pixel
+ * limit in ATSUI.
+ */
+#define ATSUI_OVERRUNNING_GLYPH_FLAG 0x100000
 
 /**
  * Calculate the advance in appunits of a run of ATSUI glyphs
@@ -561,7 +650,8 @@ GetAdvanceAppUnits(ATSLayoutRecord *aGlyphs, PRUint32 aGlyphCount,
 static void
 SetGlyphsForCharacterGroup(ATSLayoutRecord *aGlyphs, PRUint32 aGlyphCount,
                            Fixed *aBaselineDeltas, PRUint32 aAppUnitsPerDevUnit,
-                           gfxTextRun *aRun, const PRPackedBool *aUnmatched,
+                           gfxTextRun *aRun, PRUint32 aSegmentStart,
+                           const PRPackedBool *aUnmatched,
                            const PRUnichar *aString)
 {
     NS_ASSERTION(aGlyphCount > 0, "Must set at least one glyph");
@@ -593,7 +683,7 @@ SetGlyphsForCharacterGroup(ATSLayoutRecord *aGlyphs, PRUint32 aGlyphCount,
     if (!allMatched) {
         for (i = firstOffset; i <= lastOffset; ++i) {
             PRUint32 index = i/2;
-            aRun->SetMissingGlyph(index, aString[index]);
+            aRun->SetMissingGlyph(aSegmentStart + index, aString[index]);
         }
         return;
     }
@@ -605,9 +695,9 @@ SetGlyphsForCharacterGroup(ATSLayoutRecord *aGlyphs, PRUint32 aGlyphCount,
         if (!inOrder) {
             // Because the characters in this group were not in the textrun's
             // required order, we must make the entire group an indivisible cluster
-            aRun->SetCharacterGlyph(index, g.SetClusterContinuation());
+            aRun->SetCharacterGlyph(aSegmentStart + index, g.SetClusterContinuation());
         } else if (!aRun->GetCharacterGlyphs()[index].IsClusterContinuation()) {
-            aRun->SetCharacterGlyph(index, g.SetLigatureContinuation());
+            aRun->SetCharacterGlyph(aSegmentStart + index, g.SetLigatureContinuation());
         }
     }
 
@@ -619,7 +709,7 @@ SetGlyphsForCharacterGroup(ATSLayoutRecord *aGlyphs, PRUint32 aGlyphCount,
             (!aBaselineDeltas || aBaselineDeltas[displayGlyph - aGlyphs] == 0) &&
             gfxTextRun::CompressedGlyph::IsSimpleAdvance(advance) &&
             gfxTextRun::CompressedGlyph::IsSimpleGlyphID(displayGlyph->glyphID)) {
-            aRun->SetCharacterGlyph(index, g.SetSimpleGlyph(advance, displayGlyph->glyphID));
+            aRun->SetCharacterGlyph(aSegmentStart + index, g.SetSimpleGlyph(advance, displayGlyph->glyphID));
             return;
         }
     }
@@ -647,20 +737,24 @@ SetGlyphsForCharacterGroup(ATSLayoutRecord *aGlyphs, PRUint32 aGlyphCount,
     }
     if (detailedGlyphs.Length() == 0) {
         NS_WARNING("No glyphs visible at all!");
-        aRun->SetCharacterGlyph(index, g.SetMissing());
+        aRun->SetCharacterGlyph(aSegmentStart + index, g.SetMissing());
         return;
     }
 
     detailedGlyphs[detailedGlyphs.Length() - 1].mIsLastGlyph = PR_TRUE;
     detailedGlyphs[detailedGlyphs.Length() - 1].mAdvance =
         GetAdvanceAppUnits(advanceStart, aGlyphs + aGlyphCount - advanceStart, aAppUnitsPerDevUnit);
-    aRun->SetDetailedGlyphs(index, detailedGlyphs.Elements(), detailedGlyphs.Length());    
+    aRun->SetDetailedGlyphs(aSegmentStart + index, detailedGlyphs.Elements(), detailedGlyphs.Length());    
 }
 
-static void
+/**
+ * Returns true if there are overrunning glyphs
+ */
+static PRBool
 PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
                    const PRUnichar *aString, PRBool aWrapped,
-                   const PRPackedBool *aUnmatched)
+                   const PRPackedBool *aUnmatched,
+                   PRUint32 aSegmentStart, PRUint32 aSegmentLength)
 {
     // AutoLayoutDataArrayPtr advanceDeltasArray(aLine, kATSUDirectDataAdvanceDeltaFixedArray);
     // Fixed *advanceDeltas = NS_STATIC_CAST(Fixed *, advanceDeltasArray.mArray);
@@ -672,7 +766,7 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
     PRUint32 numGlyphs = glyphRecordsArray.mItemCount;
     if (numGlyphs == 0 || !glyphRecordsArray.mArray) {
         NS_WARNING("Failed to retrieve key glyph data");
-        return;
+        return PR_FALSE;
     }
     ATSLayoutRecord *glyphRecords = NS_STATIC_CAST(ATSLayoutRecord *, glyphRecordsArray.mArray);
     NS_ASSERTION(!baselineDeltas || baselineDeltasArray.mItemCount == numGlyphs,
@@ -681,7 +775,7 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
                  "Last glyph should be a terminator glyph");
     --numGlyphs;
     if (numGlyphs == 0)
-        return;
+        return PR_FALSE;
 
     PRUint32 appUnitsPerDevUnit = aRun->GetAppUnitsPerDevUnit();
     PRBool isRTL = aRun->IsRightToLeft();
@@ -690,18 +784,19 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
         // The glyph array includes a glyph for the artificial trailing
         // non-whitespace character. Strip that glyph from the array now.
         if (isRTL) {
-            NS_ASSERTION(glyphRecords[0].originalOffset == aRun->GetLength()*2,
+            NS_ASSERTION(glyphRecords[0].originalOffset == aSegmentLength*2,
                          "Couldn't find glyph for trailing marker");
             glyphRecords++;
         } else {
-            NS_ASSERTION(glyphRecords[numGlyphs - 1].originalOffset == aRun->GetLength()*2,
+            NS_ASSERTION(glyphRecords[numGlyphs - 1].originalOffset == aSegmentLength*2,
                          "Couldn't find glyph for trailing marker");
         }
         --numGlyphs;
         if (numGlyphs == 0)
-            return;
+            return PR_FALSE;
     }
 
+    PRUint32 allFlags = 0;
     // Now process the glyphs, which should basically be in
     // the textrun's desired order, so process them in textrun order
     PRInt32 direction = PRInt32(aRun->GetDirection());
@@ -713,6 +808,7 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
         while (glyphCount < numGlyphs) {
             ATSLayoutRecord *glyph = &glyphRecords[glyphIndex + direction*glyphCount];
             PRUint32 glyphOffset = glyph->originalOffset;
+            allFlags |= glyph->flags;
             // Always add the current glyph to the group if it's for the same
             // character as a character whose glyph is already in the group,
             // or an earlier character. The latter can happen because ATSUI
@@ -722,7 +818,7 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
             // In this case we need to make sure the glyph for the consonant
             // is added to the group containing the vowel.
             if (lastOffset < glyphOffset) {
-                if (!aRun->IsClusterStart(glyphOffset/2)) {
+                if (!aRun->IsClusterStart(aSegmentStart + glyphOffset/2)) {
                     // next character is a cluster continuation,
                     // add it to the current group
                     lastOffset = glyphOffset;
@@ -747,13 +843,13 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
             SetGlyphsForCharacterGroup(glyphRecords + numGlyphs - glyphCount,
                                        glyphCount,
                                        baselineDeltas ? baselineDeltas + numGlyphs - glyphCount : nsnull,
-                                       appUnitsPerDevUnit, aRun, aUnmatched,
-                                       aString);
+                                       appUnitsPerDevUnit, aRun, aSegmentStart,
+                                       aUnmatched, aString);
         } else {
             SetGlyphsForCharacterGroup(glyphRecords,
                                        glyphCount, baselineDeltas,
-                                       appUnitsPerDevUnit, aRun, aUnmatched,
-                                       aString);
+                                       appUnitsPerDevUnit, aRun, aSegmentStart,
+                                       aUnmatched, aString);
             glyphRecords += glyphCount;
             if (baselineDeltas) {
                 baselineDeltas += glyphCount;
@@ -761,17 +857,23 @@ PostLayoutCallback(ATSULineRef aLine, gfxTextRun *aRun,
         }
         numGlyphs -= glyphCount;
     }
+    
+    return (allFlags & ATSUI_OVERRUNNING_GLYPH_FLAG) != 0;
 }
 
 struct PostLayoutCallbackClosure {
     gfxTextRun                  *mTextRun;
     const PRUnichar             *mString;
-    // This is true when we inserted an artifical trailing character at the
-    // end of the string when computing the ATSUI layout.
-    PRPackedBool                 mWrapped;
     // Either null or an array of stringlength booleans set to true for
     // each character that did not match any fonts
     nsAutoArrayPtr<PRPackedBool> mUnmatchedChars;
+    PRUint32                     mSegmentStart;
+    PRUint32                     mSegmentLength;
+    // This is true when we inserted an artifical trailing character at the
+    // end of the string when computing the ATSUI layout.
+    PRPackedBool                 mWrapped;
+    // The callback *sets* this to indicate whether there were overrunning glyphs
+    PRPackedBool                 mOverrunningGlyphs;
 };
 
 // This is really disgusting, but the ATSUI refCon thing is also disgusting
@@ -784,17 +886,21 @@ PostLayoutOperationCallback(ATSULayoutOperationSelector iCurrentOperation,
                             void *iOperationCallbackParameterPtr, 
                             ATSULayoutOperationCallbackStatus *oCallbackStatus)
 {
-    PostLayoutCallback(iLineRef, gCallbackClosure->mTextRun,
-                       gCallbackClosure->mString, gCallbackClosure->mWrapped,
-                       gCallbackClosure->mUnmatchedChars);
+    gCallbackClosure->mOverrunningGlyphs =
+        PostLayoutCallback(iLineRef, gCallbackClosure->mTextRun,
+                           gCallbackClosure->mString, gCallbackClosure->mWrapped,
+                           gCallbackClosure->mUnmatchedChars,
+                           gCallbackClosure->mSegmentStart,
+                           gCallbackClosure->mSegmentLength);
     *oCallbackStatus = kATSULayoutOperationCallbackStatusContinue;
     return noErr;
 }
 
-void
+PRBool
 gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
                                const PRUnichar *aString, PRUint32 aLength,
-                               PRBool aWrapped)
+                               PRBool aWrapped, PRUint32 aSegmentStart,
+                               PRUint32 aSegmentLength)
 {
     OSStatus status;
     gfxAtsuiFont *atsuiFont = GetFontAt(0);
@@ -802,17 +908,16 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
     nsTArray<ATSUStyle> stylesToDispose;
     PRUint32 headerChars = aWrapped ? 1 : 0;
     const PRUnichar *realString = aString + headerChars;
-    PRUint32 realLength = aRun->GetLength();
-    NS_ASSERTION(realLength == aLength - (aWrapped ? 3 : 0),
+    NS_ASSERTION(aSegmentLength == aLength - (aWrapped ? 3 : 0),
                  "Length mismatch");
 
 #ifdef DUMP_TEXT_RUNS
-    NS_ConvertUTF16toUTF8 str(realString, realLength);
+    NS_ConvertUTF16toUTF8 str(realString, aSegmentLength);
     NS_ConvertUTF16toUTF8 families(mFamilies);
     printf("%p(%s) TEXTRUN \"%s\" ENDTEXTRUN\n", this, families.get(), str.get());
 #endif
 
-    UniCharCount runLengths = realLength;
+    UniCharCount runLengths = aSegmentLength;
     ATSUTextLayout layout;
     // Create the text layout for the whole string, but only produce glyphs
     // for the text inside LRO/RLO - PDF, if present. For wrapped strings
@@ -821,7 +926,7 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
     status = ATSUCreateTextLayoutWithTextPtr
         (aString,
          headerChars,
-         realLength + (aWrapped ? 1 : 0),
+         aSegmentLength + (aWrapped ? 1 : 0),
          aLength,
          1,
          &runLengths,
@@ -833,6 +938,8 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
     closure.mTextRun = aRun;
     closure.mString = realString;
     closure.mWrapped = aWrapped;
+    closure.mSegmentStart = aSegmentStart;
+    closure.mSegmentLength = aSegmentLength;
     NS_ASSERTION(!gCallbackClosure, "Reentering InitTextRun? Expect disaster!");
     gCallbackClosure = &closure;
 
@@ -868,8 +975,8 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
     /* Now go through and update the styles for the text, based on font matching. */
 
     UniCharArrayOffset runStart = headerChars;
-    UniCharCount totalLength = runStart + realLength;
-    UniCharCount runLength = realLength;
+    UniCharCount totalLength = runStart + aSegmentLength;
+    UniCharCount runLength = aSegmentLength;
 
     //fprintf (stderr, "==== Starting font maching [string length: %d]\n", totalLength);
     while (runStart < totalLength) {
@@ -882,7 +989,7 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
         if (status == noErr) {
             //fprintf (stderr, "ATSUMatchFontsToText returned noErr\n");
             // everything's good, finish up
-            aRun->AddGlyphRun(atsuiFont, runStart - headerChars);
+            aRun->AddGlyphRun(atsuiFont, aSegmentStart + runStart - headerChars);
             break;
         } else if (status == kATSUFontsMatched) {
             //fprintf (stderr, "ATSUMatchFontsToText returned kATSUFontsMatched: FID %d\n", substituteFontID);
@@ -898,14 +1005,14 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
             ATSUSetAttributes (subStyle, 1, fontTags, fontArgSizes, fontArgs);
 
             if (changedOffset > runStart) {
-                aRun->AddGlyphRun(atsuiFont, runStart - headerChars);
+                aRun->AddGlyphRun(atsuiFont, aSegmentStart + runStart - headerChars);
             }
 
             ATSUSetRunStyle (layout, subStyle, changedOffset, changedLength);
 
             gfxAtsuiFont *font = FindFontFor(substituteFontID);
             if (font) {
-                aRun->AddGlyphRun(font, changedOffset - headerChars);
+                aRun->AddGlyphRun(font, aSegmentStart + changedOffset - headerChars);
             }
             
             stylesToDispose.AppendElement(subStyle);
@@ -913,7 +1020,7 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
             //fprintf (stderr, "ATSUMatchFontsToText returned kATSUFontsNotMatched\n");
             /* I need to select the last resort font; how the heck do I do that? */
             // Record which font is associated with these glyphs, anyway
-            aRun->AddGlyphRun(atsuiFont, runStart - headerChars);
+            aRun->AddGlyphRun(atsuiFont, aSegmentStart + runStart - headerChars);
             
             if (!closure.mUnmatchedChars) {
                 closure.mUnmatchedChars = new PRPackedBool[aLength];
@@ -937,7 +1044,7 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
     // the result of this call.
     ATSTrapezoid trap;
     ItemCount trapCount;
-    ATSUGetGlyphBounds(layout, 0, 0, headerChars, realLength,
+    ATSUGetGlyphBounds(layout, 0, 0, headerChars, aSegmentLength,
                        kATSUseFractionalOrigins, 1, &trap, &trapCount); 
 
     ATSUDisposeTextLayout(layout);
@@ -948,4 +1055,5 @@ gfxAtsuiFontGroup::InitTextRun(gfxTextRun *aRun,
         ATSUDisposeStyle(stylesToDispose[i]);
     }
     gCallbackClosure = nsnull;
+    return !closure.mOverrunningGlyphs;
 }