[cairo] color fonts and CAIRO_OPERATOR_SOURCE

[Uli Schlachter]

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