Feature request: Improve lua integration and mask selection for external raster masks

[martinus-523]

Summary

In darktable 5.2, a new module was introduced: external raster masks.
This module is a valuable addition, as it allows users to incorporate external raster masks into their image-editing workflows.

While experimenting with generating external raster masks through a Lua script, I found the current implementation of this module somewhat limited in terms of automation and mask management.

Current Behavior

At the moment:

• Darktable allows only a single global configuration to define the folder from which external raster masks are loaded.
• The process of selecting a specific external raster mask within the module cannot be automated through Lua.
• As the number of masks in the global folder increases, it becomes increasingly difficult to find and select the correct one — especially when multiple raster masks exist for a single image.

Proposed Enhancements

To make the external raster masks module more flexible and scriptable, I propose the following improvements:

1. Per-image mask folder setting
   Allow the module to define the raster mask folder on a per-image basis, rather than relying on a single global folder.

2. Lua API integration
   Enable Lua scripts to:

   • Set the raster mask folder for the current image.
   • Select a specific raster mask within the module programmatically.

Example Use Case

A Lua script could:

• Generate multiple raster masks for a specific image.
• Output these masks into a dedicated folder associated with that image.
• Set the External Raster Mask module to point to that folder.
• Automatically select one of the generated masks.

This would make it much easier for users to manage and switch between multiple masks associated with the same image, directly from within darktable.

Benefits

• Improved workflow automation through Lua.
• Easier mask management for complex image editing scenarios.
• Reduced clutter in the global mask folder.
• A more consistent and image-centric organization of raster masks.

[martinus-523]

BTW, the script that I wrote for this is currently Mac only and can be found here:
https://github.com/martinus-523/darktable-lua-scripts/blob/main/masking/create_subject_mask_macos.lua

[wpferguson]

@dterrahe the file chooser widget is not exposed to darktable.gui.action(). If we could expose it and allow setting the value of the file path/name that would take care of the automating issue.

@martinus-523 I looked briefly at the external masks module. Since I hadn't set the folder name explicitly, it defaulted to my home directory. I suspect that you could have a folder hierarchy under a top level "mask" directory, organized however you wish.

[martinus-523]

I looked briefly at the external masks module. Since I hadn't set the folder name explicitly, it defaulted to my home directory. I suspect that you could have a folder hierarchy under a top level "mask" directory, organised however you wish.

I would say that it makes sense to store the masks with the images. Not In a separate folder structure, but that is just me.

Once you select a mask, the combobox will show all the masks in the folder of the selected masks. So, if setting the mask by lua is possible, all other organisation can be with lua.

So that leaves only the request for setting the selected raster maks by lua as my feature request.

[dterrahe]

the file chooser widget is not exposed to darktable.gui.action(). If we could expose it and allow setting the value of the file path/name that would take care of the automating issue.

Exposing the file chooser button would just pop it up waiting for input. I guess what you want is changing the path and file fields directly. There's no mechanism to do that. Once the files in one directory are loaded into the combobox, we could expose that (just requires a simple dt_bauhaus_widget_set_label, and a dt_bauhaus_widget_hide_label).

We could add a quad button to the dropdown to just reset it to the default directory and refresh. Then you could manipulate that default via the plugins/darkroom/segments/def_path conf entry. That would be a bit confusing in the ui, so maybe it should be "hidden" behind a ctrl or right-click, which is easy to trigger in a script. The "normal" function of the quad button would then replace the current separate button. (of course I haven't checked why a separate button was used instead of the quad. There may have been a very good reason for it, who knows, but the usual drawback that it can't be placed in the QAP applies).

So if we did that the script would do:

• set conf value to directory
• dt.gui.action("...", "button", "ctrl-on")
• dt.gui.action("...", "selection", "file you want")