compositor

Arlen compositor is a fork of cosmic-comp, the Wayland compositor from System76's COSMIC desktop. It adds an Event Bus integration layer that emits structured events for window and clipboard activity.

This repo is not a GitHub fork. It is a standalone repo with cosmic-comp tracked as a git remote so we can pull upstream changes without being coupled to their branching model.

What's changed from upstream

All changes are documented in PORTING.md. The short version:

• src/event_bus.rs: new file. Background thread that connects to the Arlen Event Bus and emits events. Non-blocking: if the Event Bus is not running, events are dropped silently.
• src/state.rs: EventBusHandle added to Common
• src/shell/focus/mod.rs: emits window.focused
• src/wayland/handlers/compositor.rs: emits window.opened after map
• src/xwayland.rs: emits window.opened for XWayland windows
• src/wayland/handlers/xdg_shell/mod.rs: emits window.closed on destroy
• src/wayland/handlers/selection.rs: emits clipboard.copy on clipboard write

Events emitted

Event type	When	Payload
window.opened	Window maps (becomes visible)	app_id, title
window.focused	Input focus changes	app_id, title
window.closed	Window destroys	app_id
clipboard.copy	Clipboard content changes	none (content is not captured)

Configuration

Variable	Default	Description
ARLEN_PRODUCER_SOCKET	/run/arlen/event-bus-producer.sock	Event Bus producer socket
ARLEN_SESSION_ID	unknown	Session ID attached to all events

Staying in sync with upstream

A weekly CI workflow (.github/workflows/upstream-rebase.yml) rebases against upstream/master. On success it opens a PR. On conflict it opens an issue with label upstream-rebase-conflict.

To rebase manually:

git fetch upstream
git rebase upstream/master
# resolve conflicts if any, then push

Development

Window decorations are currently handled by cosmic-comp's built-in Iced/cosmic implementation. Replacing them with Arlen CSD via ui-kit is tracked in issue #11 and planned for Phase 2B.

Testing

cargo test
cargo clippy --all-targets --all-features -- -D warnings

Integration tests require a running X11/Wayland session and are located in distro/tests/integration_compositor.rs.

Part of

Arlen: a Linux desktop OS built around a system-wide knowledge graph.