Add AppImage build script

[TheAssassin]

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PR Description

What type of PR is this? (Check one of the boxes below)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which does not add functionality nor fixes a bug but improves Natron in some way)
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• My change requires a change to the documentation
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What does this pull request do?

See #318.

Adds an AppImage build script that converts an extracted Natron tarball into a functional AppImage.

NatronRenderer has not been exposed yet, but this is a trivial change that can be added at any time.

Have you tested your changes (if applicable)? If so, how?

The built AppImage works very well.

[devernay]

Thank you for your contribution, it's very useful!
I will add that to the standard build process as soon as it's finalized.
Feel free to answer my comments.

[devernay]

Can you add a check that verifies that the script is being executed on the right OS (I guess this is linux-only?) and architecture (x86_64 - we may support more in the future)?

[TheAssassin]

I'd rather require an $ARCH env var to be set instead, which can be evaluated in the last lines (where appimagetool is called). Detecting the architecture is horribly hard. In a CI script, one can easily add that environment variable manually, though. It's not subject to future changes.

The script can be run on any unix that can execute appimagetool (this includes FreeBSD with the linuxulator, I think). Limiting this to Linux does not make any sense to me. Could you please state how such a check would help you?

[devernay]

As you suggested, the script should also expose NatronRenderer, how easy is it?

[TheAssassin]

Depends on how you want it to work. I think some graphics utility evaluated a --executable parameter, others use environment variables. Do you have a UX in mind?

[devernay]

I never used appimage. Can NatronRenderer be in the user PATH?

[TheAssassin]

Anything is possible. For instance, you could have a wrapper that calls the AppImage.

Think of an AppImage as a filesystem image with a runtime that FUSE mounts that image and executes a defined entrypoint.

[devernay]

Please say in the help that

should be the result of... extracting the no-installer linux binary distribution?
Actually, I would like it better if the script would even take care of extracting that distribution from a downloaded file into a temp dir, and cleanup the mess at the end

[TheAssassin]

This comment seems broken, please revise.

[devernay]

Please say in the help that <dir> should be the result of... extracting the no-installer linux binary distribution(?).

Actually, the script could even take care of extracting that distribution from a downloaded file into a temp dir, and cleanup the mess at the end.

[TheAssassin]

It could, but that doesn't make sense to me, really. It might make sense in your build infrastructure, though. I do not know how you plan to integrate this.

If you need such a script, you could add it as a second script which implements the downloading, extraction etc., and then calls this script. This script follows the Unix spirit, where there should be one tool for one job, and it should do that job well.

[devernay]

Yes you're right, we should run this script at the same time we build the tarball.
What I don't understand is that there seem to be a usr/ hierarchy in the tarball, but you leave most stuff out of it.

Shouldn't everything be moved inside usr/, rather than live in bin/ docs/ etc? What's the rule for AppImage?

[TheAssassin]

Sorry for not replying in time. Feel free to move everything to a usr/ subdirectory. It's common for AppImages, maybe even "best practice", but not a requirement technically. I'll send a follow-up PR.