wl-pick

A window switcher for wlroots compositors: a grid overlay of live window previews that looks like a rofi theme, and tells you which one you picked. It replaces a wlthumbs | rofi pipeline, and doubles as a screencast source picker for the desktop portal.

No thumbnails exist. Each window is captured straight into a wl_shm buffer handed to its own wl_subsurface, and wp_viewporter tells the compositor which rectangle to scale it into — no image encoding, no scaler, no full-resolution bitmap in this process. Hence ~60 ms to appear and ~6 MB resident (peaking near 18 MB) however many windows are open.

sway-tree       0.6ms     window list + con_ids over sway IPC
toplevels       0.2ms     ext-foreign-toplevel-list handles
constraints     1.5ms     every capture session's buffer size, in one roundtrip
capture        52.5ms     8 windows, all frames in flight at once
labels          0.0ms     shaped on a worker thread while the captures ran
mapped          4.9ms     layer surface + subsurfaces on screen

Capture is the compositor reading full-resolution pixels out of the GPU: it is bandwidth-bound (~1.1 GB/s here), unaffected by how large the thumbnails are, and therefore a free window to work in — the ~20 ms of font loading and glyph rasterising happens on a worker thread inside it.

Keyboard navigation, mouse and live previews all work. Type-to-filter is the one thing the rofi version had that this doesn't — see the roadmap.

Usage

wl-pick is a chooser: the pick goes to stdout, nothing does if you cancel, and the exit status is 0 for a pick and 1 for anything else (2 if --timeout fires). It never acts on the choice — it has no idea what you want to do with it. Focusing on sway looks like this:

#!/usr/bin/env bash
# ~/.local/bin/winmenu, bound to $mod+Tab
IFS=$'\t' read -r type id toplevel app title < <(wl-pick) || exit 0
case $type in
    window) swaymsg "[con_id=$id] focus" ;;
    output) swaymsg "focus output $id" ;;
esac

Windows only, as a one-liner:

swaymsg "[con_id=$(wl-pick --no-outputs | cut -f2)] focus"

Options

Both directions of each boolean exist so either can override the config file. --hide-labels is the old spelling of --no-labels.

Output formats

The identifiers different consumers need differ, so there are three:

portal is what xdg-desktop-portal-wlr's simple chooser reads, so wl-pick can be the picker for getDisplayMedia and friends — with live previews of both windows and displays:

[screencast]
chooser_type=simple
chooser_cmd=wl-pick --format portal

Keys

Hovering deliberately does not move the selection — the keyboard keeps it, and a click acts on whatever is under the cursor. Clicking the margin, a gap, or an empty cell of a ragged last row does nothing. Navigation reads raw evdev keycodes, so it is layout-independent, but virtual-keyboard clients such as wtype cannot drive it; that goes away with the xkb support filtering needs anyway.

Starting a second wl-pick replaces the first. The new overlay takes the keyboard grab and the one that loses it exits without printing. sway answers a capture request for a toplevel another client is already capturing with silence, though, so the replacement's thumbnails stay mostly blank until the first instance has gone. Every wait on a capture is capped at two seconds for that reason: a tile that never arrives is drawn as a bare label, and the grid still works.

Live previews

Capture sessions stay open so tiles can refresh, and three things keep that cheap. It is damage-driven, so the compositor produces nothing for an idle window after the first frame. The overlay's own wl_surface.frame callbacks are the clock, so refreshes stop when it isn't being presented, with --fps throttling per tile on top. And tiles scrolled out of sight are unmapped, so they are skipped too. Measured over 4 s with one animating window in ten: 52,52,1,1,1,1,1,1,13,1 frames.

The cost is memory and bandwidth — two full-resolution buffers per window (138 MB of shm for eight windows and a display here, against 83 MB with --live none) and a readback per refreshed frame. --live current refreshes only the selected tile, which is much cheaper and still reads as alive.

Config

~/.config/wl-pick/config, or --config PATH. Flat key = value lines with # comments, everything optional, and a flag always beats the file.

background     = #282828      # the grid's backdrop
foreground     = #ebdbb2      # label text
selection      = #d79921      # the highlighted tile
selection-text = #282828      # its label
border         = #d79921
border-width   = 2px

max-width      = 90ppt        # the box the grid may fill
max-height     = 90ppt
max-columns    = 4            # thumbnails are that box divided by these
max-rows       = 4

font           = monospace
font-size      = 13.3
labels         = yes
outputs        = yes
live           = all
fps            = 12
format         = tsv
timeout        = 0            # seconds; 0 means none

Sizes take sway's units: 600px is absolute, 90ppt a percentage — resolved against the display the grid actually appears on, every time it runs, so one file gives 90% of a 1280-wide laptop panel and 90% of a 3840-wide monitor. The overlay maps explicitly on that display, at its scale, so mixed-DPI renders crisply either way.

All four sizing settings are caps: max-width/max-height bound the overlay, max-columns/max-rows bound the grid inside it. A thumbnail is that box divided by those caps, which means its size never depends on how many windows are open — one window gets the same thumbnail as thirty, in a smaller overlay, because the overlay hugs whatever is actually there. Rows past max-rows scroll, with a scrollbar in the right margin and the selection always kept in view. Turning labels off gives that row back to the thumbnails rather than shrinking the window.

Look

The defaults come from the rofi theme this replaces: gruvbox dark, a yellow selection filling the element padding, ceil(sqrt(n)) columns capped at 4, title · app centred underneath. Padding, gaps and margins are fixed, in src/theme.rs. Long titles are ellipsised to the cell.

Labels default to the system monospace — whatever fc-match monospace answers, which is what the rest of the desktop uses. --font names another, by family or by full display name: Berkeley Mono Medium SemiCondensed works as well as Berkeley Mono, because the name is split into the longest leading part that is a real family and a style read off the remainder. Weights and widths are understood joined or spaced, in any case, and a family whose own name ends in a style word — Fira Code Light — still wins over reading that word as a style. A name that matches nothing says so on stderr and falls back to the system monospace rather than shaping in an arbitrary face; --verbose reports the font actually used.

Requirements

A wlroots compositor advertising ext-image-copy-capture-v1, ext-image-capture-source-v1 (with the foreign-toplevel source manager), ext-foreign-toplevel-list-v1, wlr-layer-shell-unstable-v1 and wp_viewporter — sway 1.11+, and in principle Hyprland, labwc and jay, though only sway is tested. sway is also the source of truth for the window list, over its IPC socket, which is the one thing that would need replacing to run elsewhere (ext-foreign-toplevel-list-v1 already reports app id and title).

That socket comes from SWAYSOCK/I3SOCK when those point at something that exists, and otherwise from the running sway's socket in $XDG_RUNTIME_DIR — inheriting a stale path is easy, and a picker on a keybinding should not be the thing that notices.

Known upstream issue: holding per-toplevel capture sessions open makes windows blurry on fractionally scaled outputs (sway#9113). Integer scales are unaffected. It matters more once previews are live.

Roadmap

• type-to-filter with fzf-quality fuzzy matching (and the xkb keyboard input it needs, which would also let virtual-keyboard clients drive the overlay)
• dmabuf capture, so the pixels never leave the GPU at all — and live previews stop costing a readback per frame

Source layout

main.rs     orchestration: list, capture, map, report the pick
cli.rs      flags, defaults, and the help text that documents them
sway.rs     the window list and display names, over sway's IPC socket
target.rs   what a tile stands for, and the three output formats
app.rs      the Wayland client state every event dispatches into
capture.rs  capture sessions, their buffers, and the live clock
overlay.rs  the layer surface, the drawing, and the keyboard
theme.rs    colours, grid geometry, aspect fitting
text.rs     label shaping on a worker thread
shm.rs      memfd allocation and the ARGB painter

Building

cargo build --release
cargo test          # grid geometry, navigation and hit-testing, ellipsising,
                    # output formats, glyph output