Add 8-up support to ipptransform

[Mr-Tao]

Summary

• add an explicit 2-by-4 layout for number-up=8 in ipptransform
• document 8 as a supported number-up value
• add direct transform and virtual IPP Everywhere regression coverage

Motivation

This is the libcups companion to OpenPrinting/cups#1672. Eight-up printing is particularly useful with ISO A-series paper, where the page aspect ratio makes this imposition geometrically natural. The current libcupsfilters PDF transform already supports an explicit 8-up layout.

The new end-to-end test uses ippeveprinter, submits the existing eight-page PDF fixture with number-up=8, verifies that the job retains the attribute and completes successfully, and checks that ipptransform places all eight input pages on one output page. No physical printer is required.

Testing

• ./configure --enable-debug
• make
• make -C tools test — existing suite: 202 tests, 79 passed, 0 failed, 123 skipped; new 8-up suite: 3 passed, 0 failed
• negative control with the new case 8 temporarily removed: the regression test fails on the former 1-up fallback as expected

Related UI changes:

• GTK 4: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/10258
• GTK 3: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/10259

Assisted-by: OpenAI Codex:GPT-5 [Codex]

[michaelrsweet]

I'm really not sure how I feel about adding this at a time when things like N-up are barely used... Will consider it but certainly not before libcups 3.1.

[Mr-Tao]

Thanks for taking a look. Keeping this as a draft/Future until libcups 3.1 makes sense.

One bit of context: N-up printing is still used fairly often in university settings, especially for lecture slides and handouts, so 8-up addresses a real workflow there. I’ll be happy to rebase or adjust the implementation when 3.1 work starts.

[michaelrsweet]

I agree that slides are sometimes still printed (depending on the age of the presenter), but LibreOffice already does its own N-up generation for slides - it doesn't use the CUPS number-up option to do it...

[Mr-Tao]

That is true when printing the source presentation directly from LibreOffice; its application-side imposition covers that path. The workflow I meant is usually already-generated PDF material—slides, handouts, papers, or other documents—printed from a PDF viewer or via lp. LibreOffice is no longer involved there, so N-up has to be provided by the generic printing stack.

More generally, 8-up is the missing exact rotated layout for ISO A-series paper: a 2-by-4 grid preserves the page aspect ratio exactly, apart from margins. libcupsfilters already implements this layout. Without generic 8-up support, I have had to print 4-up to an intermediate PDF and then print that PDF 2-up; that two-stage workaround becomes particularly cumbersome with duplex output.

I understand the libcups 3.1 timing and am happy to leave this as a draft until then.