Linux: match average char width with Windows

skia/ports/SkFontHost_FreeType.cpp

 /* libs/graphics/ports/SkFontHost_FreeType.cpp
 **
 ** Copyright 2006, Google Inc.
 **
 ** Licensed under the Apache License, Version 2.0 (the "License"); 
 ** you may not use this file except in compliance with the License. 
 ** You may obtain a copy of the License at 
 **
 **     http://www.apache.org/licenses/LICENSE-2.0 
 **
@@ skipping 767 matching lines @@
 
     if (this->setupSize())
     {
         if (mx)
             memset(mx, 0, sizeof(SkPaint::FontMetrics));
         if (my)
             memset(my, 0, sizeof(SkPaint::FontMetrics));
         return;
     }
 
-    SkPoint pts[6];
-    SkFixed ys[6];
+    SkPoint pts[7];
+    SkFixed ys[7];
     FT_Face face = fFace;
     int     upem = face->units_per_EM;
     SkFixed scaleY = fScaleY;
     SkFixed mxy = fMatrix22.xy;
     SkFixed myy = fMatrix22.yy;
 
     int leading = face->height - face->ascender + face->descender;
     if (leading < 0)
         leading = 0;
 
+    // Try to get the OS/2 table from the font. This contains the specific
+    // average font width metrics which Windows uses.
+    TT_OS2* os2 = (TT_OS2*) FT_Get_Sfnt_Table(face, ft_sfnt_os2);
+
     ys[0] = -face->bbox.yMax;
     ys[1] = -face->ascender;
     ys[2] = -face->descender;
     ys[3] = -face->bbox.yMin;
     ys[4] = leading;
     ys[5] = face->height;
+    ys[6] = os2 ? os2->xAvgCharWidth : 0;
 
     // convert upem-y values into scalar points
-    for (int i = 0; i < 6; i++)
+    for (int i = 0; i < 7; i++)
     {
         SkFixed y = SkMulDiv(scaleY, ys[i], upem);
         SkFixed x = SkFixedMul(mxy, y);
         y = SkFixedMul(myy, y);
         pts[i].set(SkFixedToScalar(x), SkFixedToScalar(y));
     }
     
     if (mx)
     {
         mx->fTop = pts[0].fX;
         mx->fAscent = pts[1].fX;
         mx->fDescent = pts[2].fX;
         mx->fBottom = pts[3].fX;
         mx->fLeading = pts[4].fX;
         mx->fHeight = pts[5].fX;
+        mx->fAvgCharWidth = pts[6].fX;
 
         // The VDMX metrics only make sense in the horizontal direction
         // I believe
         my->fVDMXMetricsValid = false;
     }
     if (my)
     {
         my->fTop = pts[0].fY;
         my->fAscent = pts[1].fY;
         my->fDescent = pts[2].fY;
         my->fBottom = pts[3].fY;
         my->fLeading = pts[4].fY;
         my->fHeight = pts[5].fY;
+        my->fAvgCharWidth = pts[6].fY;
         my->fVDMXMetricsValid = false;
 
         // Attempt to parse the VDMX table to get exact metrics
         unsigned pelsize = (fScaleY + 0x8000) >> 16;
         int ymax, ymin;
         if (SkFontHost_VDMX_Parse(&ymax, &ymin, face, pelsize)) {
           my->fVDMXMetricsValid = true;
           my->fVDMXAscent = ymax;
           my->fVDMXDescent = -ymin;
         }
@@ skipping 57 matching lines @@
     }    
     if (face->style_flags & FT_STYLE_FLAG_ITALIC) {
         style |= SkTypeface::kItalic;
     }
     
     FT_Done_Face(face);
     FT_Done_FreeType(library);
     return (SkTypeface::Style)style;
 }