Universal filter: should be enabled by default?

[ValdikSS]

@michaelrsweet @tillkamppeter @zdohnal

ArchLinux builds cups-filters with default settings, which enable universal and disable individual filters.
Fedora builds without universal and with individual filters.

What should be recommended for the distros?
As far as I understand, universal is designed for CUPSv3 first and foremost. And has its own unique bugs.

[tillkamppeter]

The universal filter was an experiment some years ago to reduce external executable calls.

Should have been less resource-consuming than individual filters, but nobody actually measured it, or whether it improves performance. Also, many print workflows call only 1 or 2 filters, which would reduce the performance advantage of universal.

I switched Ubuntu to use the universal filter. It mainly worked, but there were certain drivers with too complex filter chains which made universal fail and so I switched Ubuntu back to individual filters.

So I generally recommend not to use universal in distros, for maximum compatibility with all drivers, meaning also that we should change the build system that use of individual filters is done by default and use of universal is optional.

universal is also used for filter chain tests in the CI programs, so do not remove it from the source repo, and perhaps somebody could improve it in the future to actually work with any driver, and also, in some situation, like inside a Printer Application, the cfFilterUniversal() filter function could be useful to auto-generate filter chains.

[ValdikSS]

Thanks, I'll report that to ArchLinux!

It mainly worked, but there were certain drivers with too complex filter chains which made universal fail

Do you remember which one failed?
Some proprietary filters rely on argv[0] for the printer name, that hit me twice when I made the wrappers for box86. Does universal handle that?

[tillkamppeter]

I do not actually remember which driver was the offending (or offended?) one, but AFAIR it was some proprietary one, where there were 2 filters in the chain which come from the proprietary driver package, but universal only supports a chain of libcupsfilters' filter functions plus one single driver filter.

[tillkamppeter]

Note that I did not actually design universal for CUPS 3.x but for saving resources when CUPS 2.x calls filters, as I said above. It can be used in Printer Applications though.

Note that CUPS 3.x does away with PPDs and driver filters, so it will not use the filter mechanism of CUPS 2.x, and so our filters here will mainly be used in Printer Applications and Scanner Applications in the future.