The Tumbler package contains a D-Bus thumbnailing service based on the thumbnail management D-Bus specification. This is useful for generating thumbnail images of files.

Tumbler has since version 0.1.27 a configuration file to control the priority, locations and file sizes the plugin is used for: tumbler.rc.

To override the default configuration, located in one of the xdg directories on your system, you can copy the rc-file to your $XDG_CONFIG_HOME directory.

NB: $XDG_CONFIG_HOME defaults to ~/.config.

mkdir -p $XDG_CONFIG_HOME/tumbler
cp /etc/xdg/tumbler/tumbler.rc $XDG_CONFIG_HOME/tumbler/

Each group in the configuration file is responsible for the settings of a particular thumbnailer plugin. The following keys can be used to adjust a plugin:

Disabled

Disable the plugin, the values true and false are accepted.

Priority

Numeric value to control the priority of the plugin. If 2 plugins can provide thumbnails for the same scheme + mime-type combination, the plugin with the highest priority is used first.

Locations

A ;-separated path list the plugin will be used for. If the source file is not a child of one of the locations, the plugin won't be used and another plugin with a lower priority will be tried. Absolute paths, environment variables, ~/ and ~username/ are allowed. Leave empty to allow all locations.

MaxFileSize

Maximum size of the source file the plugin will still try to generate a plugin for. The size is in bytes, 0 disabled the check.

By the default the cover thumbnailer is disabled. The reason is that it sends information (movie title extracted from the filename) to online services to retrieve a poster. This information is normally harmless, but it is private, so therefore it's not enabled by default.

In order to use the cover thumbnailer you need to copy the tumbler.rc file to your home directory as described above and set the Disabled key to false. It is also advisable to set the Locations path to the directory where you store your movies.

[CoverThumbnailer]
Disabled=false
Priority=3
Locations=~/movies
MaxFileSize=0
#APIKey=your-api-key-from-themoviedb.org

The movie thumbnailer supports two different movie APIs. By default, the The Open Movie Database API is used. You can also choose to use The Movie DB, but this site requires an API key which you have to request or uh… search.
The advantage of the latter is that their database has better support for internationalized movie names.

After creating the rc file, it is best to log off and on again to restart Thunar and Tumbler, because both applications cache the mime-type combinations.

As of version 0.2.0, the desktop thumbnailer functionality has been added back into tumbler. This functionality supports custom .thumbailer files placed in the /usr/share/thumbnailers folder.

For example, to create a custom thumbnailer for .dds files, do the following:

1. Create the appropriate .thumbnailer file:

   /usr/share/thumbnailers/dds.thumbnailer

   [Thumbnailer Entry]
   Version=1.0
   Encoding=UTF-8
   Type=X-Thumbnailer
   Name=dds Thumbnailer
   MimeType=image/x-dds;
   Exec=/usr/bin/convert -thumbnail %s %i %o

2. Ensure that a dds mimetype exists in your system (you can view mimetypes with the Xfce4 Mime Type Editor). If it does not exist, create the necessary mime file:

   ~/.local/share/mime/packages/dds.xml

   <?xml version="1.0" encoding="UTF-8"?>
   <mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
       <mime-type type="image/x-dds">
           <comment>dds file</comment>
           <icon name="image"/>
           <glob-deleteall/>
           <glob pattern="*.dds"/>
       </mime-type>
   </mime-info>

   …and run “update-mime-database ~/.local/share/mime”.

Another example are albums cover thumbnails for folders in a music collection. Starting with thunar 1.8.2 a custom thumbnailer can be added to e.g. add a file folder.jpg or cover.jpg into a folder and display its thumbnail instead of the default folder icon:

/usr/share/thumbnailers/folder.thumbnailer

[Thumbnailer Entry]
Version=1.0
Encoding=UTF-8
Type=X-Thumbnailer
Name=Folder Thumbnailer
MimeType=inode/directory;
Exec=/usr/bin/folder-thumbnailer %s %i %o %u

In order to support different names for the picture-file and to remove the thumbnail if not needed any more (display the default folder icon) , a separate script is required:

/usr/bin/folder-thumbnailer

#!/bin/bash
 
convert -thumbnail "$1" "$2/folder.jpg" "$3" 1>/dev/null 2>&1 ||\
convert -thumbnail "$1" "$2/.folder.jpg" "$3" 1>/dev/null 2>&1 ||\
convert -thumbnail "$1" "$2/folder.png" "$3" 1>/dev/null 2>&1 ||\
convert -thumbnail "$1" "$2/cover.jpg" "$3" 1>/dev/null 2>&1 ||\
rm -f "$HOME/.cache/thumbnails/normal/$(echo -n "$4" | md5sum | cut -d " " -f1).png" ||\
rm -f "$HOME/.thumbnails/normal/$(echo -n "$4" | md5sum | cut -d " " -f1).png" ||\
rm -f "$HOME/.cache/thumbnails/large/$(echo -n "$4" | md5sum | cut -d " " -f1).png" ||\
rm -f "$HOME/.thumbnails/large/$(echo -n "$4" | md5sum | cut -d " " -f1).png" ||\
exit 1

Note: imagemagick is a required dependency for this script.

A thumbnailer for text-based documents can be created using the convert function from the imagemagick package with the following thumbnailer file:

/usr/share/thumbnailers/text.thumbnailer

[Thumbnailer Entry]
Version=1.0
Encoding=UTF-8
Type=X-Thumbnailer
Name=Text Thumbnailer
MimeType=text/plain;text/html;text/css;
Exec=/usr/local/bin/textthumb %s %i %o

And supporting script:

/usr/local/bin/textthumb

#!/bin/bash
iFile=$(<"$2")
iChopped="${iFile:0:1600}"
unset iFile
echo "${iChopped}" > tmp.txt
unset iChopped
convert -size 210x290 -background white -pointsize 5 -border 10x10 -bordercolor "#CCC" caption:@"tmp.txt" "$3"
rm tmp.txt

You can add additional mime types to the MimeType line of the thumbnailer file to support additional text-based document types.