GS 9.53 and transparency

[Bruno Voisin]

> Thank you very much for sharing the notice.  This is indeed very
> relevant.  I maintain PGF/TikZ which also uses .setopacityalpha in the
> dvips backend, so it is great to know about it beforehand.
> 
> Do you know whether .set(fill|stroke)constantalpha are available in
> older versions of GS?  Then I can at least be somewhat backwards
> compatible in PGF.

They appeared in between the release of gs 9.21 (March 2017) and 9.22 (October 2017). I think they appeared in this commit

	http://git.ghostscript.com/?p=ghostpdl.git;a=commitdiff;h=7918a01dd37bc383e61ae0b237341e69286dc83c

which is mentioned in the history at

	https://www.ghostscript.com/doc/9.52/History9.htm#Version9.22

(look for "2016-07-04 09:28:06 +0100"), though the description doesn't mention the new operators.

They're still undocumented apparently: the doc at

	https://www.ghostscript.com/doc/current/Language.htm

only mentions setopacityalpha.

I've no idea whether the new operators have always provided the same functionality since gs 9.22. Also, they require now gs to be called with -dALLOWPSTRANSPARENCY, before that it was -dNOSAFER, and before that they required nothing.

In any case this is all (the recent transparency fix removing setopacityalpha) in the development version only, I don't know how things will evolve, it was more a heads up.

Bruno Voisin