Thumbnails

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Creating custom thumbnailers

Most package mangers accept the Thumbnail Managing Standard, by using it you can create your own thumbnailer for any file format, this can be done by:

1. First you need to figure out how to create a .png image from a file in the desired format.
2. Create a .thumbnailer file in $XDG_DATA_DIRS/thumbnailers.
3. Restart your thumbnailer service (This is specific to each file manager) and test if it's working.

Example

You could create a thumbnailer for Krita's .kra file format like so:

.kra are zip files, with a preview stored at /preview.png, we can use unzip to extract the preview:

unzip -p robot-squirrel.kra preview.png > robot-squirrel.png

Create a .thumbnailer file in any $XDG_DATA_DIRS/thumbnailers directory.

# $HOME/.local/share/thumbnailers/kra.thumbnailer
[Thumbnailer Entry]
Exec=sh -c "unzip -p %i preview.png > %o"
MimeType=application/x-krita;

Restart your thumbnailer service (This is specific to each file manager) and test if it's working.

After you have a working definition, you can make it reproducible like so:

# configuration.nix
{ pkgs, ... }: {
  environment.systemPackages = [
    (
      pkgs.writeTextFile {
        # This can be anything, it's just the name of the derivation in the nix store
        name = "krita-thumbnailer";
        # This is the important part, the path under which this will be installed
        destination = "/share/thumbnailers/kra.thumbnailer";
        # The contents of your thumbnailer, don't forget to specify the full path to executables
        text = ''
          [Thumbnailer Entry]
          Exec=sh -c "${pkgs.unzip}/bin/unzip -p %i preview.png > %o"
          MimeType=application/x-krita;
        '';
      }
    )
  ];
}