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..c76ba9c4d2f9064c0624b989ac90361ed0bf69a5 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -48,6 +48,13 @@
 #define GEN_ID_INC_EVAL(expression)
 #endif
 
+#define setFontMetricsBitSet(__fObject, __bitSet)       \
+{                                                                                        \
+    if(__fObject != NULL) {                                                \
+        __fObject->fFontMetricsFlag |= __bitSet;             \
+    }                                                                                     \
+}
+
 SkPaint::SkPaint() {
     // since we may have padding, we zero everything so that our memcmp() call
     // in operator== will work correctly.
@@ -1285,17 +1292,20 @@ SkScalar SkPaint::getFontMetrics(FontMetrics* metrics, SkScalar zoom) const {
     }
 
     paint.descriptorProc(NULL, zoomPtr, FontMetricsDescProc, metrics, true);
+    metrics->fFontMetricsFlag = 0;
 
     if (scale) {
-        metrics->fTop = SkScalarMul(metrics->fTop, scale);
-        metrics->fAscent = SkScalarMul(metrics->fAscent, scale);
-        metrics->fDescent = SkScalarMul(metrics->fDescent, scale);
-        metrics->fBottom = SkScalarMul(metrics->fBottom, scale);
-        metrics->fLeading = SkScalarMul(metrics->fLeading, scale);
-        metrics->fAvgCharWidth = SkScalarMul(metrics->fAvgCharWidth, scale);
-        metrics->fXMin = SkScalarMul(metrics->fXMin, scale);
-        metrics->fXMax = SkScalarMul(metrics->fXMax, scale);
-        metrics->fXHeight = SkScalarMul(metrics->fXHeight, scale);
+        if( (metrics->fTop = SkScalarMul(metrics->fTop, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_Top); };
+        if( (metrics->fAscent = SkScalarMul(metrics->fAscent, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_Ascent); };
+        if( (metrics->fDescent = SkScalarMul(metrics->fDescent, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_Descent); };
+        if( (metrics->fBottom = SkScalarMul(metrics->fBottom, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_Bottom); };
+        if( (metrics->fLeading = SkScalarMul(metrics->fLeading, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_Leading); };
+        if( (metrics->fAvgCharWidth = SkScalarMul(metrics->fAvgCharWidth, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_AvgCharWidth); };
+        if( (metrics->fXMin = SkScalarMul(metrics->fXMin, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_XMin); };
+        if( (metrics->fXMax = SkScalarMul(metrics->fXMax, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_XMax); };
+        if( (metrics->fXHeight = SkScalarMul(metrics->fXHeight, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_XHeight); };
+        if( (metrics->fUnderlineThickness = SkScalarMul(metrics->fUnderlineThickness, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_UnderlineThickness); };
+        if( (metrics->fUnderlinePosition = SkScalarMul(metrics->fUnderlinePosition, scale)) ) { setFontMetricsBitSet(metrics, kFontMetrics_UnderlinePosition); };
     }
     return metrics->fDescent - metrics->fAscent + metrics->fLeading;
 }
@@ -2257,6 +2267,14 @@ const SkRect& SkPaint::doComputeFastBounds(const SkRect& origSrc,
     return *storage;
 }
 
+bool SkPaint::isFontMetricsBitSet(FontMetrics * fObject, FontMetricsBitSet bitSet) const
+{
+    if(fObject != NULL) {
+        return SkToBool(fObject->fFontMetricsFlag & bitSet);
+    }
+    return false;
+}
+
 #ifdef SK_DEVELOPER
 void SkPaint::toString(SkString* str) const {
     str->append("<dl><dt>SkPaint:</dt><dd><dl>");