Re: Using pango in KMSCON (terminal-emulator)

[Behdad Esfahbod <behdad behdad org>]

On 13-02-22 09:45 AM, David Herrmann wrote:
> Hi Behdad

Hi David,

Minor comments below.

> On Tue, Feb 19, 2013 at 8:28 AM, Behdad Esfahbod <behdad behdad org> wrote:
> > > 4) It's important that I get full access to the 2D buffer of the
> > > glyph. I sometimes need to change stride/size/etc. and the
> > > hardware-blitters have different constraints. Hence, I cannot use any
> > > opaque "glyph"/gtk/etc. structures but instead need _direct_ buffer
> > > access.
> >
> > You can get that with pangocairo.  I hear you want to do your own blitting.
> > That's fine.
>
> So you mean I should allocate a cairo_image_surface_t, draw to it and
> then use the buffer of the image_surface? Yeah, ok, that sounds about
> right.

Correct.


> > > 3) How am I notified about font-updates in the system? If the
> > > currently used font is updated I'd like to clear my cache and let
> > > pango re-render the glyphs.
> >
> > For fontconfig changes, you can do something like this:
> >
> > http://git.gnome.org/browse/gnome-settings-daemon/tree/plugins/xsettings/fontconfig-monitor.c
>
> Awesome! Thanks! dnotify/inotify on the font-config files, few-seconds
> timeout to combine multiple notifications and then clear the caches.
> One thing is missing though: You don't update the monitor itself if
> the configuration changes? Is that on purpose? There might be new
> font-directories or configuration files that we should add to the
> monitor.

Humm.  Isn't that done here:

        if (fontconfig_cache_update ()) {
                notify = TRUE;
                monitors_free (handle->monitors);
                handle->monitors = monitors_create (data);
        }


> Also, which pango object do I need to recreate on change? Everything
> down to the font-map?

pango_fc_font_map_cache_clear() should do it.  You would also need to notify
PangoContext / PangoLayout that "some things changed" by calling their
changed() method.  Or just recreate those, since I assume you would need one
at a time.


> > > 4) What should I use as default render-mode? High-DPI (>300?) no AA
> > > but subpixel? Low-DPI AA but no subpixel? I have actually no idea what
> > > looks best... And what to do if I cannot get DPI or subpixel-layout
> > > information for a display?
> >
> > If anything, you should enable subpixel for low DPI and siable for high.  It's
> > tricky though.  Best to not try to out-guess the user.  Just do nothing?
>
> I recently read your article about font-rendering with high DPI and
> was wondering what to do. But maybe that decision belongs to
> font-config and pango, and I should just let them chose the default
> and not care at all. Users can always use font-configurations to
> overwrite it, anyway.

The problem I was addressing had constraints such as linear layout and metric
compatibility.  None applies to your application AFAIU.

Cheers,
behdad

> Thanks a lot for your help! I will give pangocairo a try.
> Regards
> David

-- 
behdad
http://behdad.org/