Re: Pango and non-system fonts

[Behdad Esfahbod <behdad behdad org>]

On Thu, 2007-08-30 at 11:03 -0400, Mike Branciforte wrote:
> All of this has been very helpful, thanks. Now back to my original
> post. If and when Pango does support non-system fonts, i.e.,
> 
> http://bugzilla.gnome.org/show_bug.cgi?id=347237
> 
> would that circumvent the manual glyph positioning required to set
> text with only Cairo?

No.  PDF has glyph positions fixed into it.

> It would be really cool to be able to do
> (speaking in pseudo-code)
> 
> setFont();
> moveto()
> showString()
> 
> Any hope for this in the near future?

You can do this with Poppler.  Pango is the wrong library to look into.

> Or is text just to darn complicated?

Text is too darn complicated, but this is not an example of it.  Glyph
positioning that is just adding numbers is very trivial compared to all
the shaping and other stuff that pango does.

> Thanks again for the helpful responses. I'll be digging back into the
> PDF spec to better understand the text operators.
> 
> Mike

behdad



> On 8/24/07, Behdad Esfahbod <behdad behdad org> wrote:
> > On Thu, 2007-08-23 at 14:08 -0400, Mike Branciforte wrote:
> > > On 8/22/07, Behdad Esfahbod <behdad behdad org> wrote:
> > > > On Wed, 2007-08-22 at 11:55 -0400, Mike Branciforte wrote:
> > > > > We are exploring the possibility of using Cairo+Pango to render pages
> > > > > from a PDF document.
> > > >
> > > > You don't need / shouldn't use pango for rendering PDF.  Pango is used
> > > > to convert characters to glyphs and to lay text out.  PDF on the other
> > > > hand, includes layed-out glyphs.  Just show it, using
> > > > cairo_show_glyphs()
> > >
> > > You lost me. Where are the "layed-out glyphs" in this PDF fragment
> > > that would show the string "Where are the glyphs?" in a PDF viewer?
> >
> > So, Owen already answered this elegantly.  I'll just add a few words to
> > it.
> >
> >
> > > q
> > > BT
> > > 50 792 Td
> > > 0 -18 Td
> > > /F1 12 Tf
> > > (Where are the glyphs?)Tj
> > > ET
> > > Q
> >
> > The (Where are the glyphs) bytes are neither characters, nor glyphs, but
> > they do choose glyphs, in a  font-specific way described in the PDF
> > standard.  Try producing a PDF with the ligature for the 'fi' sequence
> > and see how it's not human-readable anymore.  Read the PDF standard Text
> > chapter and you'll get it all.  I summarized some of it a while back, it
> > may help:
> >
> > http://lists.cairographics.org/archives/cairo/2007-February/009452.html
> >
> > Also, the Tj operator can be best thought of as an optimization for the
> > more general text operators, that computes the position of glyphs based
> > on *natural advance width* of the glyphs, as defined in the PDF font
> > structure (not the font file).
> >
> >
> > > It seems that in order to use cairo_show_glyphs() then I would have to
> > > create an array of glyphs, one "glyph" for each character in the
> > > phrase "Where are the glyphs?"? That means I would have to compute the
> > > x and y position for each glyph? Sounds like a lot of work. Am I
> > > missing something?
> >
> > It's not really a lot of work.  If you have the width array, glyph
> > position computing is as trivial as:
> >
> >  glyph[i].x = glyph[i-1].x + width[glyph[i].index];
> >  glyph[i].y = glyph[i-1].y;
> >
> >
> > > Mike
> > --
> > behdad
> > http://behdad.org/
> >
> > "Those who would give up Essential Liberty to purchase a little
> >  Temporary Safety, deserve neither Liberty nor Safety."
> >        -- Benjamin Franklin, 1759
> >
> >
> >
> >
-- 
behdad
http://behdad.org/

"Those who would give up Essential Liberty to purchase a little
 Temporary Safety, deserve neither Liberty nor Safety."
        -- Benjamin Franklin, 1759