Not all printers listed in print module

[michmill1970]

Describe the bug

Not all my printers are listed in the print module printer dropdown. The list changes every time I start Darktable. Sometimes I see only my fax print driver. Occasionally I see my fax and my default printer (HP 8020). Only once have I seen all 3 printers listed: Epson XP-15000, HP 8020 printer, and HP 8020 fax.

Steps to reproduce

1. Go to Other->Print
2. click on the printer list drop-down list

Expected behavior

Show all printers

Logfile | Screenshot | Screencast

Commit

Unknown. First time printing with Darktable

Where did you obtain darktable from?

downloaded from www.darktable.org

darktable version

4.8.1

What OS are you using?

Mac

What is the version of your OS?

14.5 (23F79)

Describe your system?

M1 Max MacBook Pro, 16" screen, 64GB RAM, 1TB NVME

Are you using OpenCL GPU in darktable?

Yes

If yes, what is the GPU card and driver?

Apple M1 Max

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

No response

[ralfbrown]

Darktable uses CUPS (Common Unix Printing System) to talk to your printers, so the first thing to check is whether CUPS is properly listing your printers. With a web browser, visit http://localhost:631/printers/ and check whether the list is correct (enable Javascript if necessary).

[michmill1970]

Yes, CUPS is listing all the printers correctly.

[ralfbrown]

We'll need someone familiar with the print module to take a look at the code.

I have a suspicion that the code is being confushed by having two 8020's in the printer list. Assuming that those are separate devices rather than multiple drivers sharing one device, what happens if you turn off one of them before starting darktable?

[michmill1970]

The two 8020's are the same physical device, but one is for fax and the other is for printing. I deleted the fax driver, and I turned off the HP 8020. Now I don't get any printers listed in Darktable.

[ralfbrown]

Sorry, out of ideas now, since I've never worked on the print module.

[michmill1970]

Do you have a suggested work-around?

1. Save the image with sRGB output color profile. Open image in GIMP or MacOS Preview, and print using the ICC profile for my printer/paper?
2. Save the image with the ICC printer/paper color profile. Open image in GIMP or MacOS Preview and use default printer settings?
3. Save the image with the ICC printer/paper color profile. Open image in GIMP or MacOS Preview, and print using the ICC profile for my printer/paper? (So use the profile for both saving and printing)
4. Other options?

I just bought a larger format printer, and I'm trying to make some prints for my mother's 85th birthday.

[michmill1970]

I was finally able to find time to create a MacOS M1 development VM. I can see the printer being returned by CUPS. I can see that prt->pinfo appears to be properly populated in _expose_print_page function in print.c. I'm still trying to learn how the UI is stitched together to understand why the printer dropdown isn't getting populated.

Who owns the print module? Maybe they can point me where to look? Where to set some breakpoints to check values and examine logic?

[ralfbrown]

3. Save the image with the ICC printer/paper color profile. Open image in GIMP or MacOS Preview, and print using the ICC profile for my printer/paper? (So use the profile for both saving and printing)

That's likely to produce the best results if you don't get darktable working in time. But I'd try all three of your suggested profiling options on small (e.g 4x6) test prints.

A quick look indicates that @TurboGit did most of the recent work on the printing-related code.

[michmill1970]

I'm at a complete loss as to why it's behaving like this. On startup in print_settings.c in function _set_printer, I see the line dt_get_printer_info(printer_name, &ps->prt.printer); return successfully with ps->prt.printer fully populated.

In _new_printer_callback I see the line dt_bauhaus_combobox_add(d->printers, printer->name); called with the printer name.

However, in _printer_changed, the line const gchar *printer_name = dt_bauhaus_combobox_get_text(combo); returns null, so _set_printer (self, printer_name); never gets called from _printer_changed, but _set_printer is being called from _new_printer_callback on initial load. I'm not sure why it's returning null if it was previously set.

I'm happy to do a Facetime, Teams, whatever with a dev who knows more about this than I do to help debug.

[TurboGit]

Indeed, I'm the original author of this module and I have done quite some work on it after it landed into darktable 2.0 on 2015. I don't have time to look at this at the moment, but will try to help early September if not solved at this point.

[TurboGit]

Some questions that could help...

• Have you tried a previous release?
• Has this been working at some point?
• ...

[michmill1970]

@TurboGit I have not tried a previous release. I can, but I have a significant number of images edited with 4.8.1 and I would prefer to not lose the history.

What's most odd about this issue is it only happens with 1 particular printer, my Epson XP-15000, which is brand new. I've been using 2 other printers for a long time and have never had this issue. I'm wondering if it's not related to the fact the Epson is a wide-format printer, and something elsewhere in the code can't handle the wider formats. I'll start looking in that direction.

Observed results:

• If the only printer configured in MacOS is the Epson XP-15000, the printer drop-down is always empty.
• If I have the Epson and HP OfficeJet Pro 8020 configured in the OS, then sometimes I get the HP, and sometimes the dropdown is empty.
• If I have only the HP OfficeJet Pro 8020 configured in the OS, then it always works.