Milad Alizadeh
25d90bdcec
Click a tile to pick it, scroll to move the selection. Hovering does not move the selection: the keyboard keeps that, and a click acts on whatever is under the cursor instead. A click on the margin, on a gap, or on an empty cell of a ragged last row does nothing. Tiles are already subsurfaces, so a click on a thumbnail identifies its tile by which surface the event arrived on — no hit-testing needed. Only the chrome around them (padding, labels, gaps) needs Layout::hit, which inverts the same maths elem() lays out with, and is tested against it. Picking waits for press and release on the same tile, so sliding off a tile before letting go is not a pick. wp_cursor_shape_v1 sets the pointer shape, which spares us a cursor theme and libwayland-cursor; without it the cursor keeps whatever shape the window underneath gave it. It is optional — a compositor without it just gets whatever shape was already there.
8.5 KiB
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. The difference is that no thumbnails
exist: each window is captured straight into a wl_shm buffer that is handed to
its own wl_subsurface, and wp_viewporter tells the compositor which rectangle
to scale it into. There is no image encoding, no scaler, and no full-resolution
bitmap in this process — which is also why it appears in about 60 ms and holds
~18 MB of RSS 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
The capture phase is the compositor reading full-resolution window pixels out of the GPU. It is bandwidth-bound (~1.1 GB/s here) and unaffected by how large the thumbnails are — which also makes it a free window to do other work in. Loading a font and rasterising its first glyphs costs ~20ms, so labels are shaped on a worker thread started before the captures and joined after them, and cost nothing in wall clock.
Status
Working: a labelled grid of live previews with keyboard navigation. Type-to-filter is the one thing the rofi version had that this doesn't — see the roadmap.
Usage
wl-pick [--format tsv|json|portal] [--live all|current|none] [--fps N]
[--no-outputs] [--hide-labels] [--font FAMILY] [--font-size PX]
[--timeout SECS] [--verbose]
--format tsv|json|portalhow to report the pick (defaulttsv)--live all|current|nonewhich tiles keep updating (defaultall; displays are always a single snapshot)--fps Ncap on live updates per tile per second (default 12)--no-outputswindows only; displays are included as tiles by default--hide-labelsdraws an icon-only grid--font FAMILYlabel font family (defaultBerkeley Mono)--font-size PXlabel size in logical px--timeout SECSexits after a deadline, in case the keyboard grab ever traps you--verbosephase timings, the tile list, and capture stats
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 a cancel. 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"
Three formats, because the identifiers different consumers need differ:
--format |
output |
|---|---|
tsv (default) |
TYPE⇥ID⇥TOPLEVEL_ID⇥APP⇥TITLE — ID is the sway con_id, or the output name for a display; TOPLEVEL_ID is the ext-foreign-toplevel-list-v1 identifier that grim -T and the portal capture by |
json |
the same record with every key always present, for jq |
portal |
Monitor: NAME or Window: TOPLEVEL_ID |
portal is exactly 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
| key | |
|---|---|
→ ← / l h / Tab Shift+Tab |
next / previous tile |
↓ ↑ / j k |
move a row |
Home End |
first / last |
Enter |
pick the selection |
Escape / q |
cancel |
| click | pick that tile |
| scroll | next / previous tile |
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. Tiles are subsurfaces, so a click on a thumbnail identifies its tile by surface; only clicks on the chrome around them need hit-testing.
Navigation reads raw evdev keycodes, so it is layout-independent — but it also
means virtual-keyboard clients such as wtype (which invent their own keymap)
cannot drive it. That goes away with xkb support, which filtering needs anyway.
Live previews
Capture sessions stay open, so a tile can be refreshed. Three things keep that from being expensive:
- It is damage-driven. After a session's first frame the compositor only
produces another once the window content changes, so a request left
outstanding on an idle window costs nothing. Measured over 4s with one
animating window out of ten:
52,52,1,1,1,1,1,1,13,1frames — the static windows delivered exactly their first frame and nothing more. - Frame callbacks are the clock. Re-captures are driven by the overlay's own
wl_surface.framecallbacks, so they stop when it isn't being presented, and--fpsthrottles per tile on top of that (12 fps measured as 12.1). - Two buffers per window, alternating. A capture must not write into a buffer
the compositor is reading, so each window gets two and
wl_buffer.releasedecides which is free. Note that release is the entire contract: withwl_shmthe compositor copies the pixels out at commit and hands the buffer straight back, so the slot on screen is usually free too — waiting for it to stop being displayed instead deadlocks after two 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.
Look
Colours, font metrics and grid geometry come from the rofi theme this replaces
(gruvbox dark, a yellow selection filling the element padding, ceil(sqrt(n))
columns capped at 4, 16:9 tiles, title · app centred underneath) and live in
src/theme.rs, which is the one place to change them. They are not
configurable at runtime beyond the font flags.
The font is looked up by family name. Your own font directories are scanned first because they are small; the full system scan (~37ms) happens only if the family isn't found there, and an unknown family then falls back to whatever cosmic-text picks rather than failing. Long titles are ellipsised to the cell.
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).
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 and hit-testing, ellipsising, output
# formats, glyph output