GS 9.53 and transparency

[Bruno Voisin]

There's finally a fix for the transparency bug in Ghostscript 9.51 and 9.52, at

	https://bugs.ghostscript.com/show_bug.cgi?id=702219
	https://git.ghostscript.com/?p=ghostpdl.git;a=commit;h=d12d2085b5bd08ca1e813d97f3f7f7e630e791a0

The fix is in progress, it's for the pdfwrite device and they're working on the x11 device.

Looking closer (in particular the reworked transparency_example.ps), the fix seems to remove setopacityalpha, which forms the basis of pstricks' transparency support for gs, and setshapealpha, replacing them by setfillconstantalpha and setstrokeconstantalpha. So much for backward compatibility!

To be sure, I compiled the development version and tried several example files:

	transparency_example.ps from the gs source
	one example by Herbert Voss from <https://tug.org/pipermail/tex-live/2020-March/045044.html>
	another example by Herbert Voss from <https://bugs.ghostscript.com/show_bug.cgi?id=702218#c4>
	an example by Alexander Grahn from <https://bugs.ghostscript.com/show_bug.cgi?id=702218#c0>
	a pstricks test file (attached) posted to the MacTeX list by Herbert Schulz last year

With transparency_example.ps, transparency is obtained with -dALLOWPSTRANSPARENCY, none with -dNOSAFER. I think that's how it's supposed to be.

The two examples by Herbert Voss return

	Error: /undefined in .setopacityalpha

which is logical given gs no longer defines setopacityalpha.

The pstricks example by Herb Schulz, and the example by Alexander Grahn (probably the dvips output of a pstricks file), yield no error but there's no transparency in the PDF output, with or without -dALLOWPSTRANSPARENCY.

I'm not gonna do anything about it, I'm not a pstricks user myself, I'm just the guy who deals (together with Dick Koch) with Ghostscript compilation for the MacTeX group. I thought it useful to report this here though, so that people from this list could interact with the Ghostscript people if need be.

Bruno Voisin
(please cc me for replies, I'm not on the list)

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