[pstricks] exclamation mark

[Alan Ristow]

Doris Wagner wrote:
> hi list,
> 
> sometimes in pstricks-code there are expressions like this:
> 
> linecolor=gray!20
> 
> I guess that the exclamation mark is something postscript-specific. Can 
> anyone explain the meaning of this exclamation mark or tell me where I 
> can find something about it in the web?

There are at least two different uses of the exclamation mark that are 
often used pstricks macros, one related to Postscript and the other to 
xcolor. The use above is from xcolor and specifies that the linecolor be 
20% gray. You can learn about that use from the xcolor manual.

The other common use lets you use Postscript code to specify coordinates 
and angles to pstricks macros. For example:

\rput(!x 1 add x 2 mul){A}

will use x+1 as its x-coordinate and 2x as its y-coordinate. Of course, 
x has to be defined somehow (e.g., by \psplot or via custom definition 
using \pstVerb). To learn more, see the section in the pstricks manual 
dealing with coordinates, specifically \SpecialCoor. Also, see the 
Examples section at http://www.pstricks.de -- look for "PostScript 
procedures" and download the accompanying .tex file.

Alan