RE: Linear Scaling of fonts with FreeType on Cairo

["Karl Reis" <kreight1-msu yahoo com>]

Thank you for your excellent reply!  I modified the code per your
suggestions and it worked perfectly.  Here is the full snippet of code for
anyone else who might find this useful:

    cairo_font_options_t    *options;
    cairo_t                 *cr;
    PangoFontMap            *fm;
    PangoContext            *context;
    PangoLayout             *layout;
    PangoFontDescription    *pfd;

    cr = gdk_cairo_create (pixmap);

    fm = pango_cairo_font_map_get_default ();
    pango_cairo_font_map_set_resolution (PANGO_CAIRO_FONT_MAP(fm), 96);
    context = pango_cairo_font_map_create_context
(PANGO_CAIRO_FONT_MAP(fm));

    options = cairo_font_options_create ();
    cairo_font_options_set_hint_style (options, CAIRO_HINT_STYLE_NONE);
    cairo_font_options_set_hint_metrics (options, CAIRO_HINT_METRICS_OFF);
    pango_cairo_context_set_font_options (context, options);

    layout = pango_layout_new (context);
    pango_layout_set_text (layout,text_string,-1);

    pfd = pango_font_description_new ();
    pango_font_description_set_size (pfd,12*PANGO_SCALE*scale_factor);
    pango_layout_set_font_description (layout,pfd);

    cairo_move_to (cr, x, y);
    pango_cairo_show_layout (cr,layout);

So, I guess I ended up using some default font which I presume is not a
freetype font.  But, it worked.  To answer your question below, I did check
for NULL and indeed the font map created was NULL.... which means as you
indicate that the cairo I have is not compiled with the freetype backend
enabled.  For what it's worth, I also tried it with the "TOY" font and I got
the same error.

I am running on mingw windows with the binaries derived straight from Tor's
page.

Thanks again for your help,

Karl

> -----Original Message-----
> From: Behdad Esfahbod [mailto:behdad esfahbod gmail com] On Behalf Of
> Behdad Esfahbod
> Sent: Thursday, December 06, 2007 2127 PM
> To: Karl Reis
> Cc: gtk-app-devel-list gnome org
> Subject: Re: Linear Scaling of fonts with FreeType on Cairo
> 
> On Thu, 2007-12-06 at 19:01 -0800, Karl Reis wrote:
> > I'm trying to find a way to scale fonts linearly.  As far as I can tell,
> the
> > way to do it is to use a freetype font and turn hinting off.  Using the
> API,
> > I tried to pull some code together that would try to do that, but
> > unfortunately, the font is still scaling non-linearly.
> 
> You're on the right track.  All font backends are supposed to support
> that but I'm not sure how non-freetype ones handle it right now.
> 
> 
> >     cairo_font_options_t *options;
> >
> >     PangoFontMap            *fm;
> >
> >     PangoContext            *context;
> >
> >
> >
> >     fm = pango_cairo_font_map_new_for_font_type (CAIRO_FONT_TYPE_FT);
> >
> >     pango_cairo_font_map_set_resolution (PANGO_CAIRO_FONT_MAP(fm), 96);
> >
> >     context = pango_cairo_font_map_create_context
> > (PANGO_CAIRO_FONT_MAP(fm));
> >
> >
> >
> >     options = cairo_font_options_create ();
> >
> >     cairo_font_options_set_hint_style (options, CAIRO_HINT_STYLE_NONE);
> >
> >     pango_cairo_context_set_font_options (context, options);
> >
> > During runtime I receive the following error:
> >
> > Pango-CRITICAL **: pango_cairo_font_map_create_context: assertion
> > `PANGO_IS_CAIRO_FONT_MAP (fontmap)' failed
> 
> What's your platform?  This pretty much means that
> pango_cairo_font_map_new_for_font_type() returned NULL, which according
> to the docs, means that pango detected at compile time that your cairo
> isn't compiled with the freetype font backend enabled.
> 
> Most of the time you just need pango_cairo_font_map_get_default().
> 
> 
> > Specifically, how can I use a PangoCairoFontMap in such a scenario?  The
> > documentation states that I should be getting such a structure upon
> calling
> > pango_cairo_font_map_new_for_font_type.  However, all I get is a
> > PangoFontMap.  I'm not sure what the difference is between these two
> > structures and/or if one can be type cast onto another.
> 
> PangoCairoFontMap is a PangoFontMap.  Think object-oriented programming.
> 
> 
> > More generally, how can I scale fonts linearly using the Pango, Cairo
> API?
> 
> You are setting hint_style.  That affects rendering of the glyphs but
> not their extents.  You should turn metrics hinting off for that.
> cairo_font_options_set_hint_metrics().
> 
> 
> > Tutorials, guides would be very helpful.
> 
> A tutorial is in the works right now, but far from complete:
> 
>   http://bugzilla.gnome.org/show_bug.cgi?id=502222
> 
> > Thanks,
> >
> >
> >
> > Karl
> 
> 
> Have fun with pangocairo!
> 
> --
> behdad
> http://behdad.org/
> 
> ...very few phenomena can pull someone out of Deep Hack Mode, with two
> noted exceptions: being struck by lightning, or worse, your *computer*
> being struck by lightning.  -- Matt Welsh