Take style into account when matching fonts

third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp

Index: third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp b/third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp
index 2840a61a4330ecf81b1610978817d38652cd573d..3de39caf2ece4bded7c0a9d3eedadfdec5590aef 100644
--- a/third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp
+++ b/third_party/WebKit/Source/platform/fonts/FontFallbackList.cpp
@@ -150,12 +150,43 @@ const SimpleFontData* FontFallbackList::determinePrimarySimpleFontData(const Fon
     }
 }
 
+unsigned evaluateFontMatch(const FontDescription& desiredFont, PassRefPtr<FontData> actualFont)
+{
+    const SkFontStyle& actualStyle = actualFont->fontDataForCharacter(' ')->platformData().typeface()->fontStyle();
+    // TODO: use desiredFont.skiaFontStyle();
+
+    // Blink maps font weights into [0,8], with 3 being 'normal' (400).
+    // Skia maps the same font weights into [100,900] with 400 being 'normal'.
+    int fontWeightScore = abs((desiredFont.weight() + 1) - (actualStyle.weight() / 100));
+    if (fontWeightScore == 1)
+        fontWeightScore = 0; // Allow for a small amount of tolerance.
+    if (fontWeightScore > 3)
+        fontWeightScore *= 10; // Larger weight differenecs are disproportionately bad.
+
+    int fontStretchScore = abs(desiredFont.stretch() - actualStyle.width()); // Skia and Blink agree on the definition of font stretch
+    if (fontStretchScore == 1)
+        fontStretchScore = 0; // Allow for a small amount of tolerance.
+    if (fontStretchScore > 3)
+        fontStretchScore *= 3; // Larger stretch differences are bad, but not as noticeable as weight differences.
+
+    // We allow italic and oblique to substitute for each other, but substituting either for upright/normal is undesirable.
+    int fontSlantScore = 0;
+    if ((desiredFont.style() == FontStyleNormal) != (actualStyle.slant() == SkFontStyle::kUpright_Slant))
+        fontSlantScore += 50;
+
+    return fontWeightScore + fontStretchScore + fontSlantScore;
+}
+
 PassRefPtr<FontData> FontFallbackList::getFontData(const FontDescription& fontDescription, int& familyIndex) const
 {
     const FontFamily* currFamily = &fontDescription.family();
     for (int i = 0; currFamily && i < familyIndex; i++)
         currFamily = currFamily->next();
 
+    int bestMatchIndex = cAllFamiliesScanned;
+    unsigned bestMatchScore = UINT_MAX;
+    RefPtr<FontData> bestMatch;
+
     for (; currFamily; currFamily = currFamily->next()) {
         familyIndex++;
         if (currFamily->family().length()) {
@@ -164,10 +195,22 @@ PassRefPtr<FontData> FontFallbackList::getFontData(const FontDescription& fontDe
                 result = m_fontSelector->getFontData(fontDescription, currFamily->family());
             if (!result)
                 result = FontCache::fontCache()->getFontData(fontDescription, currFamily->family());
-            if (result)
-                return result.release();
+            if (result) {
+                unsigned fontMatchScore = evaluateFontMatch(fontDescription, result);
+                if (fontMatchScore == 0)
+                    return result.release();
+                if (fontMatchScore < bestMatchScore) {
+                    bestMatch = result;
+                    bestMatchScore = fontMatchScore;
+                    bestMatchIndex = familyIndex;
+                }
+            }
         }
     }
+    if (bestMatchScore != UINT_MAX) {
+        familyIndex = bestMatchIndex;
+        return bestMatch.release();
+    }
     familyIndex = cAllFamiliesScanned;
 
     if (m_fontSelector) {