komorebi for KDE

A tiling window manager for KDE Plasma on Wayland, in the family of komorebi for Windows and komorebi for Mac. The daemon decides where each window goes, and KWin, the window manager of Plasma, does the moving and the drawing.

Installing it

On NixOS, the flake's module, services.komorebi, installs komorebi and komorebic and starts komorebi with every Plasma session: one flake input, one module line and services.komorebi.enable = true. Elsewhere, both are built from source. docs/installation.md has both ways. There are no prebuilt binaries: the Komorebi license does not allow third parties to redistribute them.

Running it locally

nix develop
cargo run --bin komorebi --locked -- --version
cargo run --bin komorebi --locked -- --log-level debug
cargo run --bin komorebi --locked -- --fake-backend

Inside a Plasma Wayland session, komorebi loads a script into KWin, reads the monitors and the windows that are open, tiles them, and tiles the windows again whenever one opens, closes, takes the focus, is minimized or comes back, until it is stopped with Ctrl-C. It needs KWin 6.8 or newer; docs/dev/PLATFORM.md has what it expects of the session. Outside a Plasma session it exits with an error that says what is missing. --fake-backend runs the window manager against an in-memory desktop with one monitor and no windows instead.

While it runs, the daemon takes messages on a Unix socket, komorebi.sock in $XDG_RUNTIME_DIR/komorebi (the local data directory when there is no runtime directory): a message can ask for the state of the window manager, ask which monitor, workspace or container has the focus, give the focus to another window, move the focused window to another tile, change the layout, resize a tile, float a window, retile every monitor, or stop the daemon. komorebi-client writes them, and komorebic, the command line, is how a person sends them. komorebic start runs the komorebi on the PATH, and passes it what follows a --. In a Plasma session:

cargo build --locked
export PATH="$PWD/target/debug:$PATH"
komorebic start
komorebic state
komorebic stop

komorebic start -- --fake-backend tries the daemon and komorebic without a compositor, against the in-memory desktop.

nix develop provides the Rust toolchain that rust-toolchain.toml selects, a nightly rustfmt, and the tools just check and the flake's checks use. With direnv, the .envrc does it on cd. On Linux, nix run .#komorebi -- --version builds and runs the daemon without a checkout of the toolchain.

Crates

• komorebi: the daemon, and the library behind it. The library has the vocabulary the window manager is written in (core), the Backend trait through which it reaches a compositor and the in-memory desktop the tests use (backend), the backend that reaches KWin through a script it runs and edits the one setting of KWin's it needs in the user's kwinrc (kwin), the model of what it tiles (monitor, workspace, container, window), the window manager that keeps the model (window_manager), loads it from the backend (desktop) and changes it when the compositor reports an event (window_manager_event, window_manager_event_listener, process_event), the Ring that holds monitors, workspaces and containers, and the lists in which some elements are locked in place. It answers the messages on the daemon's socket (core::SocketMessage, process_command), shows its state (state), and sends its subscribers a notification of each event and message it handles (notify_subscribers).
• komorebi-client: a library that sends messages to the daemon, reads its answers, subscribes to its notifications, and re-exports the types they are made of.
• komorebic: the command line. A subcommand that asks something of the daemon is one message on its socket; start, log, data-directory, completions and the hidden docgen work without the daemon.
• version: the version string every binary reports.

The layouts, which turn a work area and a number of containers into a rectangle for each, are komorebi-layouts from komorebi, a git dependency at the revision Cargo.toml pins.

Checks

just check runs the formatting check, clippy with warnings denied, the tests, rustdoc with warnings denied, and the type check and tests of the bridge (no package.json: tsc and node come from the dev shell), inside nix develop. nix flake check runs the same checks as derivations, plus cargo deny, the TOML and Nix formatting, the tests under cargo nextest, and nixos-module-eval, which evaluates the NixOS module in real NixOS systems, on Linux and on an Apple silicon Mac. On Linux it also boots every VM test, which needs KVM. A Mac runs the tests against the fake desktop, since KWin only exists on Linux. nix fmt formats every file the checks look at.

The VM tests boot NixOS with Plasma and run a real KWin, on machines configured with the NixOS module, so every one of them runs komorebi as the module installs it. just vm NAME runs one; docs/dev/vm-tests.md has the details, including how to run them on a Mac.

How it fits together

The daemon decides where every window goes and asks the compositor to put it there. Everything it needs from the compositor is behind one trait, Backend, so the window manager logic runs against a real compositor and against an in-memory fake desktop alike. docs/dev/ARCHITECTURE.md describes the trait and where each of its rules is enforced.

On KDE Plasma the backend is in two parts. A script that komorebi loads into KWin, the bridge, reports what KWin sees over the session bus, and carries out the commands it is given as the answer to a call it holds open. The daemon keeps a table of the windows and monitors from those reports, answers the window manager's questions from it, and turns each report into an event for the window manager. If KWin restarts, the daemon loads the bridge into the new one.

komorebi's workspaces are KWin's own virtual desktops: workspace i is desktop i, and each monitor shows a desktop of its own, which the daemon has KWin do by turning on its per-output virtual desktops (the setting is put back when the daemon stops). Showing a workspace is a request to KWin, which shows the windows of that desktop, hides the others, and gives the focus to one of them. When something else switches a monitor to another desktop (a pager, a shortcut, an application raising a window of another desktop), or puts a window on another desktop, the window manager follows.

The window manager models the desktop as monitors, each with a ring of workspaces, each with a ring of containers, each with a ring of windows. A workspace's layout gives each of its containers a tile of the monitor's work area, and every window of a container is moved onto its tile. At startup the window manager loads the monitors and the windows that are open from the backend and tiles them; after that it changes the model when the compositor reports that a window was shown, closed, focused, minimized or restored, and tiles the workspace in front again. A window open at startup goes to the workspace whose desktop it is on.

Everything else reaches the daemon as a message on its socket: one JSON SocketMessage per line, handled one at a time with the window manager locked. A message that asks a question is answered on the same connection. A message that gives an order changes the model the way an event does: focus and cycle-focus give the focus to the container on one side of the focused one in the layout, or to the next one in the workspace's order, and move and cycle-move swap the focused container with that one and tile the workspace again. change-layout, cycle-layout and flip-layout tile the workspace in another layout, layout-ratios and scrolling-layout-columns tune it, toggle-tiling stops it moving windows and starts it again, preselect-direction reserves a tile for the next window, resize-edge and resize-axis move the edges of the focused tile, promote brings the focused window to the largest tile, toggle-float takes it out of the layout, and toggle-lock keeps its container at its place. The scrolling layout is a strip of columns that runs past the edges of the monitor and scrolls to the window that has the focus. minimize and close ask KWin to minimize or close the focused window, unmanage takes it out of the layout until manage takes it back, and toggle-pause stops the daemon acting on events and orders until it is resumed. The padding commands set the gaps around the tiles, and the work area offsets keep parts of a monitor free of tiles. Rules decide which windows are managed at all: ignore-rule keeps an application out of the layout, manage-rule tiles it whatever the ignore rules say, and session-float-rule floats the focused window and the windows like it. focus-workspace shows another workspace, and move-to-workspace and send-to-workspace put the focused window on another workspace, with and without showing it; their cycle- and -last-workspace forms go to the next, the previous or the last workspace, workspace-name names a workspace for focus-named-workspace and the other named commands, and new-workspace and close-workspace add and remove one. At the edge of a monitor, focus and move cross to the monitor on that side; focus-monitor, move-to-monitor, send-to-monitor and their kind work on the monitors, and eager-focus finds the window of an application wherever it is.

A program such as a status bar can subscribe to the daemon's notifications: it listens on a socket of its own, and after each event and each message, the daemon connects to it and writes the event or the message with the state of the window manager.

On NixOS, the module nix/nixos-module.nix runs the daemon as a systemd user unit that the Plasma session starts, and systemd starts it again if it fails.

Documentation

The user guide starts at docs/index.md, docs/installation.md says how to install komorebi, and docs/cli has a page for every komorebic subcommand, which just docgen writes from the subcommands' help. cargo doc --workspace --no-deps --open builds the API documentation. CONTRIBUTING.md says how to work on the code. docs/dev/ARCHITECTURE.md describes the model, docs/dev/DESIGN.md says why it is built that way, docs/dev/PLATFORM.md what it needs from KDE Plasma, and docs/dev/vm-tests.md how the VM tests work.

License

komorebi for KDE is under the Komorebi License. Contributions are accepted under the terms in CONTRIBUTING.md.