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

include/core/SkPaint.h

Index: include/core/SkPaint.h
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index abb859950c5bb6a66aecccded690ca8cd6ae02a2..88578992d1f6fbaaec4884699aa39ad305531280 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -742,6 +742,7 @@ public:
         SkScalar    fXMax;      //!< The maximum bounding box x value for all glyphs
         SkScalar    fXHeight;   //!< The height of an 'x' in px, or 0 if no 'x' in face
         SkScalar    fCapHeight;  //!< The cap height (> 0), or 0 if cannot be determined.
+        SkScalar    fUnderlineThickness; //!< underline thickness only for scalable fonts

[bungeman-skia, 2014/02/10 19:06:22]

The underline thickness and position both come from the 'post' table, so if you
have one you have the other, seems that both should be used. Also, all versions
of the 'OS/2' table have yStrikeoutSize and yStrikeoutPosition, and it looks
like you want this as well. Interestingly, FreeType and CoreText appear not to
want to give out the strikeout metrics. I see no reason for FreeType to be doing
this, but CoreText appears to want to handle any strikeout itself. At the very
least, if adding 'underline thickness' here, 'underline position' should also be
here (even if it should probably be ignored in vertical).

The 'only for scalable fonts' here is misleading. This comment should instead
state 'underline thickness, or 0 if cannot be determined'. The scalability of
the font has little to do with this, though OpenType does require the 'post'
table be present.

[h.joshi, 2014/02/11 04:41:59]

Thank you, will modify comment and also add "underline position" calculation.
Comment "only for scalable fonts" was added as per comments in FreeType.h
"underline_position - The position, in font units, of the underline line for
this face.  It is the center of the underlining stem. 
Only relevant for scalable formats."

On 2014/02/10 19:06:22, bungeman1 wrote:

     };
 
     /** Return the recommend spacing between lines (which will be