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

src/ports/SkFontHost_FreeType.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 1366 matching lines @@
     if (os2) {
         x_height = scaleX * SkIntToScalar(os2->sxHeight) / upem;
         avgCharWidth = SkIntToScalar(os2->xAvgCharWidth) / upem;
         if (os2->version != 0xFFFF && os2->version >= 2) {
             cap_height = scaleX * SkIntToScalar(os2->sCapHeight) / upem;
         }
     }
 
     // pull from format-specific metrics as needed
     SkScalar ascent, descent, leading, xmin, xmax, ymin, ymax;
+    SkScalar underlineThickness, underlinePosition;
     if (face->face_flags & FT_FACE_FLAG_SCALABLE) { // scalable outline font
         ascent = -SkIntToScalar(face->ascender) / upem;
         descent = -SkIntToScalar(face->descender) / upem;
         leading = SkIntToScalar(face->height + (face->descender - face->ascender)) / upem;
         xmin = SkIntToScalar(face->bbox.xMin) / upem;
         xmax = SkIntToScalar(face->bbox.xMax) / upem;
         ymin = -SkIntToScalar(face->bbox.yMin) / upem;
         ymax = -SkIntToScalar(face->bbox.yMax) / upem;
+        underlineThickness = SkIntToScalar(face->underline_thickness) / upem;
+        underlinePosition = SkIntToScalar(face->underline_position) / upem;
         // we may be able to synthesize x_height and cap_height from outline
         if (!x_height) {
             FT_BBox bbox;
             if (getCBoxForLetter('x', &bbox)) {
                 x_height = SkIntToScalar(bbox.yMax) / 64.0f;
             }
         }
         if (!cap_height) {
             FT_BBox bbox;
             if (getCBoxForLetter('H', &bbox)) {
                 cap_height = SkIntToScalar(bbox.yMax) / 64.0f;
             }
         }
     } else if (fStrikeIndex != -1) { // bitmap strike metrics
         SkScalar xppem = SkIntToScalar(face->size->metrics.x_ppem);
         SkScalar yppem = SkIntToScalar(face->size->metrics.y_ppem);
         ascent = -SkIntToScalar(face->size->metrics.ascender) / (yppem * 64.0f);
         descent = -SkIntToScalar(face->size->metrics.descender) / (yppem * 64.0f);
         leading = (SkIntToScalar(face->size->metrics.height) / (yppem * 64.0f))
                 + ascent - descent;
         xmin = 0.0f;
         xmax = SkIntToScalar(face->available_sizes[fStrikeIndex].width) / xppem;
         ymin = descent + leading;
         ymax = ascent - descent;
+        underlineThickness = 0;

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

Here is where the 'unknown' flag should be set (or the 'known' flag unset)
stating that we don't know what the value is. The entire point of having the
bitfield was to avoid using this '0 means unknown' convention.

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

Okey, will make required changes.

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

+        underlinePosition = 0;
     } else {
         goto ERROR;
     }
 
     // synthesize elements that were not provided by the os/2 table or format-specific metrics
     if (!x_height) {
         x_height = -ascent;
     }
     if (!avgCharWidth) {
         avgCharWidth = xmax - xmin;
@@ skipping 11 matching lines @@
         mx->fTop = ymax * mxy;
         mx->fAscent = ascent * mxy;
         mx->fDescent = descent * mxy;
         mx->fBottom = ymin * mxy;
         mx->fLeading = leading * mxy;
         mx->fAvgCharWidth = avgCharWidth * mxy;
         mx->fXMin = xmin;
         mx->fXMax = xmax;
         mx->fXHeight = x_height;
         mx->fCapHeight = cap_height;
+        mx->fUnderlineThickness = underlineThickness;
+        mx->fUnderlinePosition = underlinePosition;
     }
     if (my) {
         my->fTop = ymax * myy;
         my->fAscent = ascent * myy;
         my->fDescent = descent * myy;
         my->fBottom = ymin * myy;
         my->fLeading = leading * myy;
         my->fAvgCharWidth = avgCharWidth * myy;
         my->fXMin = xmin;
         my->fXMax = xmax;
         my->fXHeight = x_height;
         my->fCapHeight = cap_height;
+        my->fUnderlineThickness = underlineThickness;
+        my->fUnderlinePosition = underlinePosition;
     }
 }
 
 void SkScalerContext_FreeType::emboldenIfNeeded(FT_Face face, FT_GlyphSlot glyph)
 {
     if (fRec.fFlags & SkScalerContext::kEmbolden_Flag) {
         switch ( glyph->format ) {
             case FT_GLYPH_FORMAT_OUTLINE:
                 FT_Pos strength;
                 strength = FT_MulFix(face->units_per_EM, face->size->metrics.y_scale) / 24;
@@ skipping 205 matching lines @@
         *style = (SkTypeface::Style) tempStyle;
     }
     if (isFixedPitch) {
         *isFixedPitch = FT_IS_FIXED_WIDTH(face);
     }
 
     FT_Done_Face(face);
     FT_Done_FreeType(library);
     return true;
 }