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..cbd82758d6eb5b63474b951db03d8c673cd70a28 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -1287,6 +1287,9 @@ SkScalar SkPaint::getFontMetrics(FontMetrics* metrics, SkScalar zoom) const {
     paint.descriptorProc(NULL, zoomPtr, FontMetricsDescProc, metrics, true);
 
     if (scale) {
+        // Assuming Font will have correct metrics for Underline Thickness and Position
+        metrics->fFontMetricsFlag = 0x03;
+
         metrics->fTop = SkScalarMul(metrics->fTop, scale);
         metrics->fAscent = SkScalarMul(metrics->fAscent, scale);
         metrics->fDescent = SkScalarMul(metrics->fDescent, scale);
@@ -1296,6 +1299,20 @@ 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);
+        // Following is to check if we have faulty underline thciness metrics
+        if ( (metrics->fUnderlineThickness == 0) || (metrics->fUnderlineThickness >= metrics->fAscent/2))

[bungeman-skia, 2014/02/17 19:10:06]

Why would these checks only be done when there is a 'scale'? These seem like odd
checks here in any event, it seems that the knowledge as to whether we actually
have good values should come from the port, not have some policy hard coded
here. If this is the sort of policy checks that, say, Blink would like, then
Blink should implement such a policy.

[h.joshi, 2014/02/18 05:48:48]

Added these to check faulty font metrics for Underline, as Underline is defined
for scaled fonts only so added check here, from previous comments I thought Skia
needs to check if Font has faulty Underline metrics and then set respective
flag.

On 2014/02/17 19:10:06, bungeman1 wrote:

+        {
+            metrics->fFontMetricsFlag = metrics->fFontMetricsFlag  ^ FontMetrics::kUnderlineThinknessIsValid_FontMetricFlag;
+        }
+
+        metrics->fUnderlinePosition = SkScalarMul(metrics->fUnderlinePosition, scale);
+        // Following is to check if we have faulty underlien position metrics
+        if(SkScalarAbs(metrics->fUnderlinePosition) >= (metrics->fDescent + metrics->fLeading))
+        {
+            metrics->fFontMetricsFlag = metrics->fFontMetricsFlag ^FontMetrics::kUnderlinePositionIsValid_FontMetricsflag;
+        }
     }
     return metrics->fDescent - metrics->fAscent + metrics->fLeading;
 }
@@ -2257,6 +2274,14 @@ const SkRect& SkPaint::doComputeFastBounds(const SkRect& origSrc,
     return *storage;
 }
 
+bool SkPaint::isFontMetricsFlagSet(FontMetrics * fObject, FontMetrics::FontMetricsFlags flag) const
+{
+    if(fObject != NULL) {
+        return SkToBool(fObject->fFontMetricsFlag & flag);
+    }
+    return false;
+}
+
 #ifdef SK_DEVELOPER
 void SkPaint::toString(SkString* str) const {
     str->append("<dl><dt>SkPaint:</dt><dd><dl>");