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#97 in Images

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Used in glycin

MPL-2.0 OR LGPL-2.1-or-later

729 lines


Glycin allows to decode images into gdk::Textures and to extract image metadata. The decoding happens in sandboxed modular image loaders.

  • glycin – The image library
  • glycin-utils – Utilities to write loaders for glycin
  • loaders – Glycin loaders for several formats


let file = gio::File::for_path("image.jpg");
let image = Loader::new(file).request().await?;

let height = image.info().height;
let texture = image.next_frame().await?.texture;

Image loader configuration

Loader configurations are read from XDG_DATA_DIRS and XDG_DATA_HOME. The location is typically of the from


so for example


The configs are glib KeyFiles of the the form

Exec = /usr/libexec/glycin/0+/glycin-image-rs

Where the part behind loader is a mime-type and the value of Exec can be any executable path.

Existing compatibility versions

Not every new major version of the library has to break compatibility with the loaders. The formal definition is available in docs/. The following compatibility versions currently exist


Supported image formats

The following features are supported by the glycin loaders provided in the loaders directory.

Format Decoder ICC CICP EXIF XMP Animation Library
AVIF heif libheif-rs + libheif (C++)
BMP image-rs image-rs
DDS image-rs image-rs
farbfeld no mime image-rs
QOI image-rs image-rs
GIF image-rs image-rs
HEIC heif libheif-rs + libheif (C++)
ICO image-rs image-rs
JPEG image-rs image-rs
JPEG XL jxl jpegxl-rs + libjxl (C++)
OpenEXR image-rs image-rs
PNG image-rs image-rs
PNM image-rs image-rs
SVG image-rs librsvg + gdk-pixbuf (C)
TGA image-rs image-rs
TIFF image-rs image-rs
WEBP image-rs image-rs
Symbol Meaning
Supported by format but not implemented yet
Not available for this format

Building and Testing

  • The -Dloaders option allows to only build certain loaders.
  • The -Dtest_skip_ext option allows to skip certain image filename extensions during tests. The -Dtest_skip_ext=heic might be needed if x265 is not available.
  • Running integration tests requires the glycin loaders to be installed. By default this is done by meson test automatically. This behavior can be changed by setting -Dtest_skip_install=true.
  • The glycin crate has an example, glycin-render that will load the image passed as a parameter and render it as a PNG into output.png in the current directory.


Distributions need to package the loader binaries and their configs independent of apps. The loaders build and installed via meson.

Apps will depend on the glycin crate to make use of the installed binary loaders.

Packaging Status

Inner Workings

Glycin spawns one sandboxed process per image file via bwrap or flatpak-spawn. The communication happens via peer-to-peer D-Bus over a UNIX socket. The file data is read from a GFile and sent to the sandbox via a separate UNIX socket. The texture data is provided from the sandbox via a memfd that is sealed afterward and given as an mmap to GTK. For animations and SVGs the sandboxed process is kept alive for new frames or tiles as long as needed.

To implement a new loader, please consult the glycin-utils docs.


SPDX-License-Identifier: MPL-2.0 OR LGPL-2.1-or-later


Utilities for building glycin decoders


~366K SLoC