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How do I configure Flatpak applications to interact with each other?

Here is a specific example.

The .deb version of Darktable is able to interact with the .deb versions of GIMP and Hugin Panorama Stitcher. However, the Flatpak version of Darktable cannot interact with the .deb. version of GIMP nor the Flatpak version of Hugin. In fact, there is a whole raft of functionality (provided by lua scripts that call other programs) that no longer works because it is a Flatpak.

I have installed Flatseal so that I can have some control over Flatpak applications. I have managed to give Darktable access to my home folder, which is great, but that's all I have achieved.

What do I need to do to allow Flatpak applications to work with each other?

hatterman
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    What do you mean "interact"? Are you trying to do something specific? – BeastOfCaerbannog Apr 13 '25 at 20:44
  • I mean interact in the true sense, don't know what other word to use. Darktable is able to send images to gimp and hugin, which are able in turn to send images back to darktable. But not when they are flatpaks. It seems to me that flatpaks are so isolated in their sandbox that they can't interact with other flatpaks. – hatterman Apr 15 '25 at 19:17
  • Yeah, I understand that. I meant if you have some specific example of interaction that we could try in order to see if the issue can be reproduced. Since you mention "lua scripts" but not which exactly, I'm not sure how to test the issue. Sorry for not being so clear in my comment. – BeastOfCaerbannog Apr 17 '25 at 15:09
  • Open a photo in darktable. Enable the built in lua scripts. Enable the export to gimp option. Export an image to gimp. It should automatically open in gimp. It doesn't with flatpaks, it does with traditional .deb. – hatterman Apr 22 '25 at 18:56

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I have edited this answer as it turns out, after a lot more reading and testing, that this is not an easy problem to solve.

In order for a Flatpak application to launch another Flatpak application, it needs to be spawned. In addition, certain D Bus communication permissions needs to be configured. In further addition, the spawned application needs to be able to provide feedback to the application that spawned it and to be able to read and write to its folders. As both applications are in their own restricted sandbox (that's the point of Flatpak after all) it seems this is not a trivial task.

The Darktable Github tracker does have a request made in 2024, for the Lua scripts to be Flatpak aware, as others are also missing this functionality.

hatterman
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