Adding code to calculate Underline Thickness from Font Metrics, this will be useful when Skia is us…

src/core/SkPaint.cpp

Index: src/core/SkPaint.cpp
diff --git a/src/core/SkPaint.cpp b/src/core/SkPaint.cpp
index c3f217cefc60e5501e08a88755b5f537dbcb956c..0cb9eff90520a9105cf95c3f482a39d75f5a63ce 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -1296,6 +1296,8 @@ SkScalar SkPaint::getFontMetrics(FontMetrics* metrics, SkScalar zoom) const {
         metrics->fXMin = SkScalarMul(metrics->fXMin, scale);
         metrics->fXMax = SkScalarMul(metrics->fXMax, scale);
         metrics->fXHeight = SkScalarMul(metrics->fXHeight, scale);
+        metrics->fUnderlineThickness = SkScalarMul(metrics->fUnderlineThickness, scale);
+        metrics->fUnderlinePosition = SkScalarMul(metrics->fUnderlinePosition, scale);
     }
     return metrics->fDescent - metrics->fAscent + metrics->fLeading;
 }
@@ -2257,6 +2259,18 @@ const SkRect& SkPaint::doComputeFastBounds(const SkRect& origSrc,
     return *storage;
 }
 
+void SkPaint::FontMetrics::setFontMetricsFlag(FontMetrics::FontMetricsFlags flag) {
+    fFontMetricsFlag |= flag;
+}
+
+void SkPaint::FontMetrics::unsetFontMetricsFlag(FontMetrics::FontMetricsFlags flag) {
+    fFontMetricsFlag &= ~flag;
+}
+
+bool SkPaint::FontMetrics::checkFontMetricsFlag(FontMetrics::FontMetricsFlags flag) const {
+   return SkToBool(fFontMetricsFlag & flag);

[bungeman-skia, 2014/02/20 16:52:46]

If going with the uint32_t version of these, the setters above are still good,
but this would become

SkToBool((fFontMetricsFlag & flag) == flag);

or something equivalent. I do believe that all of these implementations should
be inlined (in SkPaint.h) as they're just named bit twiddles.

+}
+
 #ifdef SK_DEVELOPER
 void SkPaint::toString(SkString* str) const {
     str->append("<dl><dt>SkPaint:</dt><dd><dl>");