[cairo] color fonts and CAIRO_OPERATOR_SOURCE

[Behdad Esfahbod]

On Wed, Sep 13, 2017 at 11:07 AM, Bill Spitzak <spitzak at gmail.com> wrote:

> On Mon, Sep 11, 2017 at 10:39 PM, Behdad Esfahbod <behdad at behdad.org>
> wrote:
> > It was actually not that complicated:
> > https://bugs.freedesktop.org/show_bug.cgi?id=102661
>
> Yes that sounds just like my second suggestion.
>
> To deal with the double-premultiply, I would just special-case OVER
> (and perhaps a few other bounded operators). They cause the current
> code to be run where it uses the glyph color+alpha as the source. All
> other compositing operators ignore the glyph color, and use the glyph
> alpha as the letter shape.
>
> SOURCE can then be used to fill the glyph shapes with a constant color.
>

I'm not sure how I feel about that.


> >
> > On Mon, Sep 11, 2017 at 1:44 AM, Uli Schlachter <psychon at znc.in> wrote:
> >>
> >> Hi everyone,
> >>
> >> yesterday I was asked to comment here:
> >>
> >> https://github.com/i3/i3/pull/2925
> >>
> >> The issue seems to be: With operator SOURCE, drawing a color glyph
> >> clears the entire surface. So, while "normal" glyphs are supposed to be
> >> a mask that is then filled, color glyphs seem to be handled as an
> >> unbounded source. This doesn't make a difference for OVER, but for lots
> >> of other operators (at least SOURCE) it obviously matters.
> >>
> >> I didn't investigate this at all. I did not even try to reproduce.
> >> Hence, this ping. Could one of you please look at this, confirm this
> >> really happens, and say what should be done about this? Thanks.
> >>
> >> And yes, in the thread on color fonts, Matthias Clasen answered one of
> >> my questions with:
> >>
> >> >> Okay... so what is the new model? What happens when I draw a color
> >> >> glyph
> >> >> with operator XOR and a red source?
> >> >
> >> >
> >> > The red source is ignored for color glyphs because they are used as
> the
> >> > source.
> >>
> >> So apparently this behaviour is by design, meaning that glyphs can only
> >> really be used with operator OVER any more (well, and some others). So
> >> let me ask this another why: Is this really a good behaviour?
> >>
> >> Oh and one more thing: Who updates cairo's docs and all the explanations
> >> on the web page? ("glyphs work like this, except when they do not").
> >>
> >> Cheers,
> >> Uli
> >>
> >> P.S.: The list of recipents is copied from the recent thread on color
> >> fonts. I have no overview of how people ended up in this list. Sorry if
> >> $YOU are the wrong recipent.
> >> P.P.S: Yes, I also included Gtk-devel-list. I vaguely remember someone
> >> saying that this stuff is relevant there. Dear moderator, sorry for the
> >> work that this causes you.
> >> --
> >> 99 little bugs in the code
> >> 99 little bugs in the code
> >> Take one down, patch it around
> >> 117 little bugs in the code
> >>   -- @irqed
> >
> >
> >
> >
> > --
> > behdad
> > http://behdad.org/
> >
> > --
> > cairo mailing list
> > cairo at cairographics.org
> > https://lists.cairographics.org/mailman/listinfo/cairo
>



-- 
behdad
http://behdad.org/
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