PS/PDF API Change Proposal: (Re: [cairo] Semantics of transparent
rjshaw at netspace.net.au
Wed Jan 18 20:40:49 PST 2006
Owen Taylor wrote:
> I can't really object too strongly to this change, since the the model
> where a PS/PDF surface matches a CAIRO_CONTENT_COLOR surface is still
> But I'm really not very comfortable with the with the idea of a
> CAIRO_CONTENT_COLOR_ALPHA PS/PDF surface; I have concerns about
> efficiency, concerns about consistency with the rest of cairo,
> and concerns about utility.
> What is destination alpha good for?
> A) It's good if you want to end up with an object with
> destination alpha. You want to draw a transparent
> clock that you'll combine with the rest of your
> desktop. This doesn't really seem relevant to printing
> to me. In the end, you are going to end up with an
> opaque piece of paper.
What about overhead transparencies or other transparent film printers?
> The final result of drawing to a PS/PDF surface does *not*
> have alpha, no matter what your best intention. (Even you print
> to overhead slides, the alpha there is just the color white,
> and has no relation to the alpha of your surface.)
If you print red with alpha=0.5, you should get a semi transparent
printout onto clear film.
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