float CanvasRenderingContext2D::getFontBaseline(
const FontMetrics& fontMetrics) const {
// If the font is so tiny that the lroundf operations result in two
// different types of text baselines to return the same baseline, use
// floating point metrics (crbug.com/338908).
// If you changed the heuristic here, for consistency please also change it
// in SimpleFontData::platformInit().
bool useFloatAscentDescent =
fontMetrics.ascent() < 3 || fontMetrics.height() < 2;
switch (state().getTextBaseline()) {
case TopTextBaseline:
return useFloatAscentDescent ? fontMetrics.floatAscent()
: fontMetrics.ascent();
case HangingTextBaseline:
// According to
// http://wiki.apache.org/xmlgraphics-fop/LineLayout/AlignmentHandling
// "FOP (Formatting Objects Processor) puts the hanging baseline at 80% of
// the ascender height"
return useFloatAscentDescent ? (fontMetrics.floatAscent() * 4.0) / 5.0
: (fontMetrics.ascent() * 4) / 5;
case BottomTextBaseline:
case IdeographicTextBaseline:
return useFloatAscentDescent ? -fontMetrics.floatDescent()
: -fontMetrics.descent();
case MiddleTextBaseline:
return useFloatAscentDescent
? -fontMetrics.floatDescent() + fontMetrics.floatHeight() / 2.0
: -fontMetrics.descent() + fontMetrics.height() / 2;
case AlphabeticTextBaseline:
default:
// Do nothing.
break;
}
return 0;
}
static inline float positionOffsetForDecoration(TextDecoration decoration, const FontMetrics& fontMetrics, float thickness)
{
// FIXME: For SVG Fonts we need to use the attributes defined in the <font-face> if specified.
// Compatible with Batik/Opera.
if (decoration == TextDecorationUnderline)
return fontMetrics.floatAscent() + thickness * 1.5f;
if (decoration == TextDecorationOverline)
return thickness;
if (decoration == TextDecorationLineThrough)
return fontMetrics.floatAscent() * 5 / 8.0f;
ASSERT_NOT_REACHED();
return 0.0f;
}