Add Light_Matter

[probonopd]

Repository: https://github.com/Auxx/light-matter

Light Matter is an HDR photo viewer for Windows, Linux and MacOS

• Stars: 28
• Latest release: 0.2.0 (2026-08-28T20:56:36Z)
• AppImage asset: LightMatter-0.2.0.AppImage
• License: MIT

Found by .github/workflows/discover-apps.yml, which looks for GitHub
repositories that publish AppImages but are not in the catalog yet. This
entry was not tested by a human; please review it before merging.

[github-actions]

✅ Test passed

@Auxx: this pull request adds the AppImage from your GitHub repository to the AppImage catalog; the test reports the following. Could you have a look?

Please check that the screenshot shows the application's main window.

Light_Matter

Compatibility: not self-contained: uses the C library of the system; uses an old AppImage runtime that needs the C library (and libfuse2) of the system; references glibc 2.25

Warnings:

• The AppImage contains no update information, so users cannot update it with AppImageUpdate or similar tools. Please consider embedding it when building the AppImage (e.g., appimagetool -u) and publishing the .zsync file next to the AppImage; see https://docs.appimage.org/packaging-guide/optional/updates.html

Commit eccc2dc. Full log

[Auxx]

@probonopd the screenshot is technically correct, but looks meh. I will make a set of good screenshots next week and will open a PR to update. This one should be fine for a few days :)

As for old C library warnings - I will take a look a bit later this year, I have a lot on my plate, atm, lol. Also I just installed Linux for proper testing, need to set it up properly first.

[probonopd]

Please put the screenshot into your AppStream file inside the AppImage; it will be picked up from there. Then ping me here for a retest. Thanks!

[Auxx]

Ah ok, will do next week. It's a first time I'm doing any Linux development, I'm a bit out of the loop, sorry.

[probonopd]

Hi @Auxx, no need to apologize at all. Welcome to Linux development, and thank you for Light Matter! Here is, step by step, how to get your own screenshots into the catalog. The AppImage documentation on AppStream has the background.

How it works: if the AppImage contains an AppStream metainfo file (a small XML file describing the app) with a <screenshots> section, the catalog shows those screenshots instead of the one our test takes. As a bonus, Linux software centers and other catalogs read this file too.

1. Put the screenshots online

Take one or more screenshots of Light Matter as PNG files, for example with the window at about 1280×720. Commit them to your repository, e.g. as docs/screenshots/main.png. Each screenshot needs a stable public URL, for example:

https://raw.githubusercontent.com/Auxx/light-matter/main/docs/screenshots/main.png

(Use your default branch's name if it isn't main, and open the URL in a browser to check that it shows the image.)

2. Create the metainfo file

Create a file build/io.github.auxx.light_matter.appdata.xml in your repository with this content. Please adjust the summary and the description; the screenshot you list first is the one the catalog shows:

<?xml version="1.0" encoding="UTF-8"?>
<component type="desktop-application">
  <id>io.github.auxx.light_matter</id>
  <metadata_license>MIT</metadata_license>
  <project_license>MIT</project_license>
  <name>Light Matter</name>
  <summary>One line saying what Light Matter does</summary>
  <description>
    <p>A few sentences about Light Matter: what it is for and what it can do.</p>
  </description>
  <launchable type="desktop-id">light-matter.desktop</launchable>
  <url type="homepage">https://github.com/Auxx/light-matter</url>
  <screenshots>
    <screenshot type="default">
      <caption>The main window</caption>
      <image>https://raw.githubusercontent.com/Auxx/light-matter/main/docs/screenshots/main.png</image>
    </screenshot>
    <!-- more <screenshot> elements (without type="default") for further screenshots -->
  </screenshots>
</component>

light-matter.desktop is the name of the desktop file that is already in your AppImage, so the software centers can connect the two.

3. Tell electron-builder to put it into the AppImage

Your AppImage is built with electron-builder. In its configuration (the "build" section of package.json, or electron-builder.yml), add under linux:

"linux": {
  "extraFiles": [
    {
      "from": "build/io.github.auxx.light_matter.appdata.xml",
      "to": "usr/share/metainfo/io.github.auxx.light_matter.appdata.xml"
    }
  ]
}

(Keep your other linux settings; just add extraFiles.)

4. Check it (optional, but quick)

After building, you can look inside the AppImage:

./LightMatter-*.AppImage --appimage-extract
ls squashfs-root/usr/share/metainfo/

The file should be listed there. If you like, you can also check the file for mistakes with appstreamcli validate --no-net build/io.github.auxx.light_matter.appdata.xml. On Debian/Ubuntu, appstreamcli comes in the package appstream.

5. Release, then ping us

Publish a new release with the new AppImage and leave a comment here. We will then re-test this pull request, and the catalog will show your screenshots.

---

About the other remarks (nothing urgent, as you said):

• Update information: the note about AppImageUpdate is just a suggestion, and not needed for the catalog. When you get to it, this page explains it.
• C library / old runtime: the AppImage still works on most current distributions. These notes are about how old or unusual a system can be for it to still run. It can be looked at whenever you have time.

Thanks again, and have fun with Linux!

---

Generated by Claude Code

[Auxx]

@probonopd Hi, just released an update with better screenshots and other stuff. I've also added auto-update, but it's not using zsync yet, but internal Electron variant. Please ping me if some other changes are advised.

[probonopd]

/retest

[github-actions]

This pull request is merged, so its entries are tested again in a new pull request: #10022. Please follow the test there (comment /retest there to test again); this conversation is locked now.