Probably, I was in a hurry and I didn't check the terminology.
PostScript calls them patterns, Lout calls them textures.
I will try learn about Ghostscript's debugging facilities, etc.
I've done my share of PostScript debugging over the years, and
it's a pain. I suggest hand-editing the output file that crashes
with stuff like this:
(entering TextureProc\n) print
...
(leaving TextureProc\n) print
It's primitive but you're in control. Also there is a PostScript
command to print the stack out which would be useful in this case.
The operand stack, that is.