Fixing superscript and subscript baseline for tiny fonts in SVG

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

 /*
  * Copyright (C) 2005, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 68 matching lines @@
                                float fontSize,
                                bool syntheticBold,
                                bool syntheticItalic)
     : m_platformData(
           FontPlatformData(fontSize, syntheticBold, syntheticItalic)),
       m_isTextOrientationFallback(false),
       m_verticalData(nullptr),
       m_hasVerticalGlyphs(false),
       m_customFontData(customData) {}
 
 void SimpleFontData::platformInit(bool subpixelAscentDescent) {

[eae, 2016/11/04 18:25:28]

bool subpixelAscentDescentForSmallSizes would be a better name given it only
triggers for acsent < 3.

[zakerinasab, 2016/11/07 18:40:26]

Done.

   if (!m_platformData.size()) {
     m_fontMetrics.reset();
     m_avgCharWidth = 0;
     m_maxCharWidth = 0;
     return;
   }
 
   SkPaint::FontMetrics metrics;
 
   m_platformData.setupPaint(&m_paint);
@@ skipping 23 matching lines @@
           parseVDMX(&vdmxAscent, &vdmxDescent, vdmxTable, vdmxSize, pixelSize))
         isVDMXValid = true;
       WTF::Partitions::fastFree(vdmxTable);
     }
   }
 #endif
 
   float ascent;
   float descent;
 
+  // For tiny fonts, the rounding of fAscent and fDescent results in equal
+  // baseline for different types of text baselines (crbug.com/338908).
+  // Please see CanvasRenderingContext2D::getFontBaseline for the heuristic.
+  subpixelAscentDescent =

[eae, 2016/11/04 18:25:28]

Please use a different name here to avoid the appearance of masking the
parameter subpixelAscentDescent.

[zakerinasab, 2016/11/07 18:40:26]

Done.

+      subpixelAscentDescent &&
+      (-metrics.fAscent < 3 || -metrics.fAscent + metrics.fDescent < 2);
+
   // Beware those who step here: This code is designed to match Win32 font
   // metrics *exactly* except:
   // - the adjustment of ascent/descent on Linux/Android
   // - metrics.fAscent and .fDesscent are not rounded to int for tiny fonts
   if (isVDMXValid) {
     ascent = vdmxAscent;
     descent = -vdmxDescent;
   } else {
-    // For tiny fonts, the rounding of fAscent and fDescent results in equal
-    // baseline for different types of text baselines (crbug.com/338908).
-    // Please see CanvasRenderingContext2D::getFontBaseline for the heuristic.
-    if (subpixelAscentDescent &&
-        (-metrics.fAscent < 3 || -metrics.fAscent + metrics.fDescent < 2)) {
-      ascent = -metrics.fAscent;
-      descent = metrics.fDescent;
-    } else {
-      ascent = SkScalarRoundToScalar(-metrics.fAscent);
-      descent = SkScalarRoundToScalar(metrics.fDescent);
-    }
+    ascent = subpixelAscentDescent ? -metrics.fAscent
+                                   : SkScalarRoundToScalar(-metrics.fAscent);
+    descent = subpixelAscentDescent ? metrics.fDescent
+                                    : SkScalarRoundToScalar(metrics.fDescent);
 #if OS(LINUX) || OS(ANDROID)
     // When subpixel positioning is enabled, if the descent is rounded down, the
     // descent part of the glyph may be truncated when displayed in a 'overflow:
     // hidden' container.  To avoid that, borrow 1 unit from the ascent when
     // possible.
     // FIXME: This can be removed if sub-pixel ascent/descent is supported.
     if (platformData().getFontRenderStyle().useSubpixelPositioning &&
         descent < SkScalarToFloat(metrics.fDescent) && ascent >= 1) {
       ++descent;
       --ascent;
     }
 #endif
   }
 
 #if OS(MACOSX)
   // We are preserving this ascent hack to match Safari's ascent adjustment
   // in their SimpleFontDataMac.mm, for details see crbug.com/445830.
   // We need to adjust Times, Helvetica, and Courier to closely match the
   // vertical metrics of their Microsoft counterparts that are the de facto
   // web standard. The AppKit adjustment of 20% is too big and is
   // incorrectly added to line spacing, so we use a 15% adjustment instead
   // and add it to the ascent.
   DEFINE_STATIC_LOCAL(AtomicString, timesName, ("Times"));
   DEFINE_STATIC_LOCAL(AtomicString, helveticaName, ("Helvetica"));
   DEFINE_STATIC_LOCAL(AtomicString, courierName, ("Courier"));
   String familyName = m_platformData.fontFamilyName();
   if (familyName == timesName || familyName == helveticaName ||
-      familyName == courierName)
-    ascent += floorf(((ascent + descent) * 0.15f) + 0.5f);
+      familyName == courierName) {
+    ascent += subpixelAscentDescent
+                  ? ((ascent + descent) * 0.15f)
+                  : floorf(((ascent + descent) * 0.15f) + 0.5f);
+  }
 #endif
 
   m_fontMetrics.setAscent(ascent);
   m_fontMetrics.setDescent(descent);
 
   float xHeight;
   if (metrics.fXHeight) {
     xHeight = metrics.fXHeight;
 #if OS(MACOSX)
     // Mac OS CTFontGetXHeight reports the bounding box height of x,
@@ skipping 150 matching lines @@
     const FontDescription& fontDescription) const {
   if (!m_derivedFontData)
     m_derivedFontData = DerivedFontData::create();
   if (!m_derivedFontData->emphasisMark)
     m_derivedFontData->emphasisMark =
         createScaledFontData(fontDescription, emphasisMarkFontSizeMultiplier);
 
   return m_derivedFontData->emphasisMark;
 }
 
+PassRefPtr<SimpleFontData> SimpleFontData::subpixelAscentDescentFontData()
+    const {
+  return SimpleFontData::create(m_platformData, m_customFontData,
+                                m_isTextOrientationFallback, true);
+}
+
 bool SimpleFontData::isTextOrientationFallbackOf(
     const SimpleFontData* fontData) const {
   if (!isTextOrientationFallback() || !fontData->m_derivedFontData)
     return false;
   return fontData->m_derivedFontData->uprightOrientation == this ||
          fontData->m_derivedFontData->verticalRightOrientation == this;
 }
 
 std::unique_ptr<SimpleFontData::DerivedFontData>
 SimpleFontData::DerivedFontData::create() {
@@ skipping 24 matching lines @@
 float SimpleFontData::platformWidthForGlyph(Glyph glyph) const {
   if (!m_platformData.size())
     return 0;
 
   static_assert(sizeof(glyph) == 2, "Glyph id should not be truncated.");
 
   return SkiaTextMetrics(&m_paint).getSkiaWidthForGlyph(glyph);
 }
 
 }  // namespace blink