Fixing superscript and subscript baseline for tiny fonts in SVG

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

Index: third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp
diff --git a/third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp b/third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp
index 560d971671948399be37b02732835171d124d411..0098b75fa8a9f862180fed1fe24d248d5df0d7ba 100644
--- a/third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp
@@ -39,6 +39,19 @@ float SVGTextLayoutEngineBaseline::calculateBaselineShift(
   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:
@@ -131,6 +144,19 @@ float SVGTextLayoutEngineBaseline::calculateAlignmentBaselineShift(
   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;