PS/PDF API Change Proposal: (Re: [cairo]
Semantics of transparent objects)
cworth at cworth.org
Fri Jan 20 12:17:08 PST 2006
On Fri, 20 Jan 2006 11:29:34 -0800, Bill Spitzak wrote:
> If you make a COLOR window, and draw CLEAR into it, do you get
> If you make a COLOR_ALPHA and draw CLEAR into it, and then copy it to a
> COLOR surface, do you get black?
"Copy" meaning what?
If you mean drawing with CAIRO_OPERATOR_SOURCE then, yes you will get
black in that case. But most of the time, people drawing one surface
to another will be using CAIRO_OPERATOR_OVER, (which is the default)
and the cleared portions will result in no change to the destination
surface in this case.
That's the kind of behavior I want to preserve and it's something that
makes a lot of intuitive sense with ink on paper.
> My proposal really amounts to changing the behavior of *all* COLOR
> surfaces so that CLEAR draws white, and so that copying a COLOR_ALPHA
> surface into the COLOR one puts c+1-a into each pixel.
Since we're post 1.0 I don't think changing the semantics of existing
surfaces is even an option.
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