bug 581087 - get true maxAdvance and aveCharWidth in DWrite font metrics. r=bas a=blocking2.0

gfx/thebes/gfxDWriteFontList.cpp

@@ -294,10 +294,7 @@ gfxDWriteFontEntry::ReadCMAP()
                                     isUnicode,
                                     isSymbol);
     }
-
-    if (tableContext) {
-        fontFace->ReleaseFontTable(tableContext);
-    }
+    fontFace->ReleaseFontTable(tableContext);
 
     mCmapInitialized = PR_TRUE;
     mHasCmapTable = NS_SUCCEEDED(rv);

gfx/thebes/gfxDWriteFonts.cpp

@@ -178,6 +178,27 @@ gfxDWriteFont::ComputeMetrics()
 
     mMetrics.maxAdvance = mAdjustedSize;
 
+    // try to get the true maxAdvance value from 'hhea'
+    PRUint8 *tableData;
+    PRUint32 len;
+    void *tableContext = NULL;
+    BOOL exists;
+    HRESULT hr =
+        mFontFace->TryGetFontTable(DWRITE_MAKE_OPENTYPE_TAG('h', 'h', 'e', 'a'),
+                                   (const void**)&tableData,
+                                   &len,
+                                   &tableContext,
+                                   &exists);
+    if (SUCCEEDED(hr)) {
+        if (exists && len >= sizeof(mozilla::HheaTable)) {
+            const mozilla::HheaTable* hhea =
+                reinterpret_cast<const mozilla::HheaTable*>(tableData);
+            mMetrics.maxAdvance = ((gfxFloat)PRUint16(hhea->advanceWidthMax) /
+                       fontMetrics.designUnitsPerEm) * mAdjustedSize;
+        }
+        mFontFace->ReleaseFontTable(tableContext);
+    }
+
     mMetrics.internalLeading = 
         ceil(((gfxFloat)(fontMetrics.ascent + 
                     fontMetrics.descent - 
@@ -193,18 +214,44 @@ gfxDWriteFont::ComputeMetrics()
     mMetrics.spaceWidth = 
         ((gfxFloat)metrics.advanceWidth /
                    fontMetrics.designUnitsPerEm) * mAdjustedSize;
-    UINT32 ucs = L'x';
-    if (SUCCEEDED(mFontFace->GetGlyphIndicesA(&ucs, 1, &glyph)) &&
-        SUCCEEDED(mFontFace->GetDesignGlyphMetrics(&glyph, 1, &metrics))) {    
-        mMetrics.aveCharWidth = 
-            ((gfxFloat)metrics.advanceWidth /
-                       fontMetrics.designUnitsPerEm) * mAdjustedSize;
-    } else {
-        // Let's just assume the X is square.
-        mMetrics.aveCharWidth = 
-            ((gfxFloat)fontMetrics.xHeight /
+
+    // try to get aveCharWidth from the OS/2 table, fall back to measuring 'x'
+    // if the table is not available
+    mMetrics.aveCharWidth = 0;
+    hr = mFontFace->TryGetFontTable(DWRITE_MAKE_OPENTYPE_TAG('O', 'S', '/', '2'),
+                                    (const void**)&tableData,
+                                    &len,
+                                    &tableContext,
+                                    &exists);
+    if (SUCCEEDED(hr)) {
+        if (exists && len >= 4) {
+            // Not checking against sizeof(mozilla::OS2Table) here because older
+            // versions of the table have different sizes; we only need the first
+            // two 16-bit fields here.
+            const mozilla::OS2Table* os2 =
+                reinterpret_cast<const mozilla::OS2Table*>(tableData);
+            mMetrics.aveCharWidth = ((gfxFloat)PRInt16(os2->xAvgCharWidth) /
                        fontMetrics.designUnitsPerEm) * mAdjustedSize;
+        }
+        mFontFace->ReleaseFontTable(tableContext);
     }
+
+    UINT32 ucs;
+    if (mMetrics.aveCharWidth < 1) {
+        ucs = L'x';
+        if (SUCCEEDED(mFontFace->GetGlyphIndicesA(&ucs, 1, &glyph)) &&
+            SUCCEEDED(mFontFace->GetDesignGlyphMetrics(&glyph, 1, &metrics))) {    
+            mMetrics.aveCharWidth = 
+                ((gfxFloat)metrics.advanceWidth /
+                           fontMetrics.designUnitsPerEm) * mAdjustedSize;
+        } else {
+            // Let's just assume the X is square.
+            mMetrics.aveCharWidth = 
+                ((gfxFloat)fontMetrics.xHeight /
+                           fontMetrics.designUnitsPerEm) * mAdjustedSize;
+        }
+    }
+
     ucs = L'0';
     if (SUCCEEDED(mFontFace->GetGlyphIndicesA(&ucs, 1, &glyph)) &&
         SUCCEEDED(mFontFace->GetDesignGlyphMetrics(&glyph, 1, &metrics))) {
@@ -214,6 +261,7 @@ gfxDWriteFont::ComputeMetrics()
     } else {
         mMetrics.zeroOrAveCharWidth = mMetrics.aveCharWidth;
     }
+
     mMetrics.underlineOffset = 
         ((gfxFloat)fontMetrics.underlinePosition /
                    fontMetrics.designUnitsPerEm) * mAdjustedSize;
@@ -239,7 +287,8 @@ gfxDWriteFont::ComputeMetrics()
     printf("    emHeight: %f emAscent: %f emDescent: %f\n", mMetrics.emHeight, mMetrics.emAscent, mMetrics.emDescent);
     printf("    maxAscent: %f maxDescent: %f maxAdvance: %f\n", mMetrics.maxAscent, mMetrics.maxDescent, mMetrics.maxAdvance);
     printf("    internalLeading: %f externalLeading: %f\n", mMetrics.internalLeading, mMetrics.externalLeading);
-    printf("    spaceWidth: %f aveCharWidth: %f xHeight: %f\n", mMetrics.spaceWidth, mMetrics.aveCharWidth, mMetrics.xHeight);
+    printf("    spaceWidth: %f aveCharWidth: %f zeroOrAve: %f xHeight: %f\n",
+           mMetrics.spaceWidth, mMetrics.aveCharWidth, mMetrics.zeroOrAveCharWidth, mMetrics.xHeight);
     printf("    uOff: %f uSize: %f stOff: %f stSize: %f supOff: %f subOff: %f\n",
            mMetrics.underlineOffset, mMetrics.underlineSize, mMetrics.strikeoutOffset, mMetrics.strikeoutSize,
            mMetrics.superscriptOffset, mMetrics.subscriptOffset);