[ft-devel] suggested improvement to FT_GlyphSlot_Embolden

[Graham Asher]

Dear FreeTypers,

I am using FT_Glyphslot_Embolden and so far it seems to work quite well.
However, the default extra boldness (1/24 em) is too great for my purposes,
and ought to be settable via an argument, because different values are
needed at different times. For example, 1/32 em is adequate for making
DejaVu Sans Bold extra-bold.

I therefore suggest the following changes.

The function declaration in ftsynth,h becomes:


  /*
  Make a glyph bolder. The argument "boldness" is a
  fixed-point value in ems. Strokes are thickened
  by this value.
  */
  FT_EXPORT( void )
  FT_GlyphSlot_Embolden( FT_GlyphSlot  slot,
 FT_Fixed  boldness );


The function itself in ftsynth.c becomes:


  FT_EXPORT_DEF( void )
  FT_GlyphSlot_Embolden( FT_GlyphSlot  slot,
 FT_Fixed  boldness )
  {
FT_Library  library = slot->library;
FT_Face face= FT_SLOT_FACE( slot );
FT_Errorerror;
FT_Pos  xstr, ystr;


if ( slot->format != FT_GLYPH_FORMAT_OUTLINE &&
 slot->format != FT_GLYPH_FORMAT_BITMAP )
  return;

/* convert boldness to pixels */
xstr = FT_MulFix( face->units_per_EM,
  face->size->metrics.y_scale );
xstr = FT_MulFix( xstr, boldness );

ystr = xstr;

if ( slot->format == FT_GLYPH_FORMAT_OUTLINE )
{
  error = FT_Outline_Embolden( &slot->outline, xstr );
  /* ignore error */

  /* this is more than enough for most glyphs; if you need accurate */
  /* values, you have to call FT_Outline_Get_CBox   */
  xstr = xstr * 2;
  ystr = xstr;
}
else if ( slot->format == FT_GLYPH_FORMAT_BITMAP )
{
  xstr = FT_PIX_FLOOR( xstr );
  if ( xstr == 0 )
xstr = 1 << 6;
  ystr = FT_PIX_FLOOR( ystr );

  error = FT_GlyphSlot_Own_Bitmap( slot );
  if ( error )
return;

  error = FT_Bitmap_Embolden( library, &slot->bitmap, xstr, ystr );
  if ( error )
return;
}

if ( slot->advance.x )
  slot->advance.x += xstr;

if ( slot->advance.y )
  slot->advance.y += ystr;

slot->metrics.width+= xstr;
slot->metrics.height   += ystr;
slot->metrics.horiBearingY += ystr;
slot->metrics.horiAdvance  += xstr;
slot->metrics.vertBearingX -= xstr / 2;
slot->metrics.vertBearingY += ystr;
slot->metrics.vertAdvance  += ystr;

if ( slot->format == FT_GLYPH_FORMAT_BITMAP )
  slot->bitmap_top += ystr >> 6;
  }


Using the new function I can then pass the boldness value 65536 / 32 = 2048
to get extra boldness of 1/32 em. I have tested these changes and they work
well.

Best wishes,

Graham Asher




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Re: [ft-devel] suggested improvement to FT_GlyphSlot_Embolden

[Werner LEMBERG]

> I am using FT_Glyphslot_Embolden and so far it seems to work quite
> well.  However, the default extra boldness (1/24 em) is too great
> for my purposes, and ought to be settable via an argument, because
> different values are needed at different times. For example, 1/32 em
> is adequate for making DejaVu Sans Bold extra-bold.
> 
> I therefore suggest the following changes.

This looks good.  However, I think a default boldness would be nice to
retain.  For example, the value 0 could indicate this.  What do you
think?

Another problem is backwards compatibility.  Inspite of being declared
as alpha code I fear that we no longer are in the situation to change
the API because it is included by default into the library :-(

What about adding a new function instead, say,
FT_Glyphslot_Set_Emboldening, to change the embolding value?


Werner


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