Glycin

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

Example

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

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

Image loader configuration

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

<data-dir>/share/glycin/<compat-version>+/conf.d/<loader-name>.conf

so for example

<data-dir>/share/glycin/0+/conf.d/glyicn-image-rs.conf

The configs are glib KeyFiles of the the form

[loader:image/png]
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

compat-version
0+
1+

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 2000	TODO	✘	—	✘	？	✘	jpeg2k? + openjpeg (C)
JPEG XL	jxl	✔	✘	✘	✘	✘	jxl-oxide
OpenEXR	image-rs	—	—	—	—	—	image-rs
PNG	image-rs	✔	✘	✔	✘	✔	image-rs
PNM	image-rs	—	—	—	—	—	image-rs
SVG	image-rs	✘	—	—	✘ *	—	librsvg + gdk-pixbuf
TGA	image-rs	—	—	—	—	—	image-rs
TIFF	image-rs	✔	—	✔	✘	—	image-rs
WEBP	image-rs	✔	—	✔	✘	✔	image-rs + libwebp (C)

Symbol	Meaning
✔	Supported
✘	Supported by format but not implemented yet
—	Not available for this format
？	Unclear if supported by format, needs research
*	Unclear if used in practice, needs research

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.

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.

License

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

glycin 1.0.0-alpha