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 "SkAdvancedTypefaceMetrics.h"
 #include "SkBitmap.h"
@@ skipping 1372 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;

[bungeman-skia, 2014/02/19 15:39:17]

At this point we know that these values are trusted.

         // 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;
+        underlinePosition = 0;

[bungeman-skia, 2014/02/19 15:39:17]

At this point we know these values are not trusted.

     } 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;
+        if(!underlineThickness)

[bungeman-skia, 2014/02/19 15:39:17]

These checks here (and below) are incorrect and the flags should be set based on
the knowledge gained above on lines 1429 and 1403.

[h.joshi, 2014/02/19 17:12:03]

Okey, Added these checks below as "face->underline_thickness" and
"face->underline_position" can be zero. Will make changes

On 2014/02/19 15:39:17, bungeman1 wrote:

+            mx->unsetFontMetricsFlag(SkPaint::FontMetrics::kUnderlineThinknessIsValid_FontMetricFlag);
+        else
+            mx->setFontMetricsFlag(SkPaint::FontMetrics::kUnderlineThinknessIsValid_FontMetricFlag);
+
+        mx->fUnderlinePosition = underlinePosition;
+        if(!underlinePosition)
+            mx->unsetFontMetricsFlag(SkPaint::FontMetrics::kUnderlinePositionIsValid_FontMetricsflag);
+        else
+            mx->setFontMetricsFlag(SkPaint::FontMetrics::kUnderlinePositionIsValid_FontMetricsflag);
     }
     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;
+        if(!underlineThickness)
+            my->unsetFontMetricsFlag(SkPaint::FontMetrics::kUnderlineThinknessIsValid_FontMetricFlag);
+        else
+            my->setFontMetricsFlag(SkPaint::FontMetrics::kUnderlineThinknessIsValid_FontMetricFlag);
+
+        my->fUnderlinePosition = underlinePosition;
+        if(!underlinePosition)
+            my->unsetFontMetricsFlag(SkPaint::FontMetrics::kUnderlinePositionIsValid_FontMetricsflag);
+        else
+            my->setFontMetricsFlag(SkPaint::FontMetrics::kUnderlinePositionIsValid_FontMetricsflag);
     }
 }
 
 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;
 }