Fixing superscript and subscript baseline for tiny fonts in SVG

third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 21 matching lines @@
 }
 
 float SVGTextLayoutEngineBaseline::calculateBaselineShift(
     const ComputedStyle& style) const {
   const SVGComputedStyle& svgStyle = style.svgStyle();
   const SimpleFontData* fontData = m_font.primaryFont();
   DCHECK(fontData);
   if (!fontData)
     return 0;
 
+  // If font size is smaller than 3, rounding ascent and descent values in
+  // SimpleFontData sets the baseline shifts for superscript and subscript to
+  // zero. In this case,  we use subpixel ascent and descent.
+  if (m_font.getFontDescription().getSize().value < 3.0) {
+    const SimpleFontData* altFontData =
+        fontData->subpixelAscentDescentFontData().get();
+    if (altFontData)
+      fontData = altFontData;
+  }
+  DCHECK(fontData);
+  if (!fontData)
+    return 0;
+
   DCHECK(m_effectiveZoom);
   switch (svgStyle.baselineShift()) {
     case BS_LENGTH:
       return SVGLengthContext::valueForLength(
           svgStyle.baselineShiftValue(), style,
           m_font.getFontDescription().computedPixelSize() / m_effectiveZoom);
     case BS_SUB:
       return -fontData->getFontMetrics().floatHeight() / 2 / m_effectiveZoom;
     case BS_SUPER:
       return fontData->getFontMetrics().floatHeight() / 2 / m_effectiveZoom;
@@ skipping 72 matching lines @@
     baseline = dominantBaselineToAlignmentBaseline(isVerticalText,
                                                    textLineLayoutParent);
     ASSERT(baseline != AB_AUTO && baseline != AB_BASELINE);
   }
 
   const SimpleFontData* fontData = m_font.primaryFont();
   DCHECK(fontData);
   if (!fontData)
     return 0;
 
+  // If font size is smaller than 3, rounding ascent and descent values in
+  // SimpleFontData sets the baseline shifts for superscript and subscript to
+  // zero. In this case,  we use subpixel ascent and descent.
+  if (m_font.getFontDescription().getSize().value < 3.0) {
+    const SimpleFontData* altFontData =
+        fontData->subpixelAscentDescentFontData().get();
+    if (altFontData)
+      fontData = altFontData;
+  }
+  DCHECK(fontData);
+  if (!fontData)
+    return 0;
+
   const FontMetrics& fontMetrics = fontData->getFontMetrics();
   float ascent = fontMetrics.floatAscent() / m_effectiveZoom;
   float descent = fontMetrics.floatDescent() / m_effectiveZoom;
   float xheight = fontMetrics.xHeight() / m_effectiveZoom;
 
   // Note: http://wiki.apache.org/xmlgraphics-fop/LineLayout/AlignmentHandling
   switch (baseline) {
     case AB_BEFORE_EDGE:
     case AB_TEXT_BEFORE_EDGE:
       return ascent;
@@ skipping 12 matching lines @@
     case AB_MATHEMATICAL:
       return ascent / 2;
     case AB_BASELINE:
     default:
       ASSERT_NOT_REACHED();
       return 0;
   }
 }
 
 }  // namespace blink