[Freetype] aligning glyphs from different fonts

[John Hunter]

I want to draw glyphs from several different font faces to a bitmap
image (sample bitmap rendering code below).  I pass in x and y to the
function code below to place the glyph in the bitmap.  I would like
the fonts to have a common vertical origin, so that glyphs from one
face appear to be on the same line as glyphs from the other.

Right now I am working with two font files (ftdump info below).  The
font files share many of the same properties: type, direction, and EM
size.  The differ, however, in their ascender, descender and
text_height, mainly in their descender and text_height.  The glyphs
from the font with the large height and low descender are appearing
too low in the rendered bitmap with respect to the glyphs from the
other font.  Currently, I'm passing in a fixed y and incrementing x by
advance.x; I assume I need to modify y by one of the global font
metrics.

Pointers to docs or examples appreciated.

Thanks,
John Hunter


freetype-2.1.3

sample code
  error = FT_Glyph_To_Bitmap(&self->glyphs[glyph->glyph_num],
                             FT_RENDER_MODE_NORMAL,
                             0,  //no additional translation
                             0  //don't destroy image
                             );

  //handle error
  FT_BitmapGlyph bitmap = (FT_BitmapGlyph)self->glyphs[glyph->glyph_num];

  draw_bitmap( &bitmap->bitmap, 
               &self->image,
               x + bitmap->left,
               y-bitmap->top);


ftdump
hunter:~/src/ft2demos-2.1.3/bin> ./ftdump ~/src/ttf/cmmi10.ttf
There is 1 face in this file.
 
----- Face number: 0 -----
 
font name entries
   family:     cmmi10
   style:      Regular
   postscript: Cmmi10
 
font type entries
   FreeType driver: truetype
   sfnt wrapped:    yes
   type:            scalable
   direction:       horizontal
   fixed width:     no
   glyph names:     yes
   EM size:         2048
   global BBox:     (-70,-512):(2146,1536)
   ascent:          1444
   descent:         -440
   text height:     2167
 
charmaps
   0: platform: 1, encoding: 0
   1: platform: 3, encoding: 1
hunter:~/src/ft2demos-2.1.3/bin> ./ftdump ~/src/ttf/cmex10.ttf
There is 1 face in this file.
 
----- Face number: 0 -----
 
font name entries
   family:     cmex10
   style:      Regular
   postscript: Cmex10
 
font type entries
   FreeType driver: truetype
   sfnt wrapped:    yes
   type:            scalable
   direction:       horizontal
   fixed width:     no
   glyph names:     yes
   EM size:         2048
   global BBox:     (-49,-6062):(2978,1581)
   ascent:          1581
   descent:         -6082
   text height:     8812
 
charmaps
   0: platform: 1, encoding: 0
   1: platform: 3, encoding: 1
hunter:~/src/ft2demos-2.1.3/bin>