[pstricks] Real transparency hack

[Jan Steffan]

Hi Manuel,

On Thursday 14 July 2005 21:31, MLuque5130 at aol.com wrote:
> The problem of the transparency seems to arouse some interest and if
> according to the message of Jan Steffan, the problem seems to be solved in
> the new versions of GhostScript, it is a good news.
My little example shows that it works in principle, but I haven't tried it
with more complex graphics yet. At the moment I believe that it would have
to be integrated deeply inside pstricks in order to work in a clean way for
both fills and strokes. But maybe I'm wrong with this :) 

> However, if you want to arrange it by yourself, it is possible.
> This problem can be dealt with by the use of coding CMYK. When two surfaces
> of different colors are superimposed, the resulting color has as components
> the addition of the respective colors as in the example below.
> It is the result of the superposition, on an overhead projector, of three
> transparencies.
> Each transparency contains only diagram.
using the subtractive CYMK model to do this is a clever idea indeed.

> Is it possible to build something of more general?  I subject this problem
> to you...
It is and it has been done (using the RGB model):
http://tug.org/PSTricks/Examples/Colors/Mixed-Colors.tex
(although only for two overlapping shapes)

The benefit of this approach would be that it works with older viewer, too 
which don't support transparency (new viewers like kpdf don't either).
The flip side that it only works for simple graphics. You'll never be able
to layer a transparent surface over a bitmap and dealing with more than two
or three overlapping shapes in a generic way is probably nontrivial.
 Jan

-- 
 gpg --keyserver subkeys.pgp.net --recv-keys DE34EFA1