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Milad Alizadeh 2cd076699d Label the tiles

"title · app" centred under each thumbnail, in the same font the rofi
theme used (Berkeley Mono at pango's "small"), with the selected tile's
label inverted onto the yellow the way rofi's element background did.
Long titles are ellipsised to the cell width.

Text comes from cosmic-text, which brings real shaping. The catch is
cost: building a font system and rasterising the first glyphs takes
~55ms, nearly doubling a 65ms startup. But the capture phase is ~55ms of
sitting blocked while the compositor copies pixels, so labels are shaped
on a worker thread started before the captures and joined after them.
The measured labels phase is now 0.0ms — it costs nothing in wall clock.

Two thirds of that font cost was FontSystem::new() scanning all 1793
system faces, which even new_with_fonts() does. So the database is built
by hand: the user's own font directories first, since they are small,
and the full system scan only when the family isn't found there. An
unknown family still resolves, because that fallback is exactly the
system scan (verified: --font "No Such Font" renders in Noto).

--hide-labels restores the icon-only grid, and --font/--font-size make
the family and size settable. Adds a test that a label actually puts
pixels on the surface, one for ellipsising, and one pinning the label row
into the element geometry.

2026-08-23 10:39:37 +01:00

4.2 KiB

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wlgrid

A window switcher for wlroots compositors: a thumbnail grid overlay that looks like a rofi theme, and focuses the window you pick.

It replaces a wlthumbs | rofi pipeline. 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 holds ~9 MB of RSS and appears in about 60 ms.

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, and usable as a switcher today: a labelled static grid with keyboard navigation. Filtering and live previews are next — see the roadmap.

Usage

wlgrid [--print] [--verbose] [--hide-labels] [--font FAMILY] [--font-size PX]
       [--timeout SECS]

--print writes the selected sway con_id to stdout instead of focusing it
--verbose prints phase timings and how many windows were captured
--hide-labels draws an icon-only grid
--font FAMILY label font family (default Berkeley Mono)
--font-size PX label size in logical px
--timeout SECS exits after a deadline (an escape hatch: the overlay takes an exclusive keyboard grab)

Bind it in sway:

bindsym $mod+Tab exec wlgrid

key
`→` `←` / `Tab` `Shift+Tab`	next / previous window
`↑` `↓`	move a row
`Home` `End`	first / last
`Enter`	focus the selection
`Escape` / `q`	cancel, leaving focus alone

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.

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. They will move to a config file so they can't drift from the .rasi.

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 and for focusing, over its IPC socket.

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

M3 type-to-filter with fzf-quality fuzzy matching (and xkb keyboard input)
M4 live previews: keep the capture sessions open and re-capture on a rate limit, --live all|current|none
M5 dmabuf capture, so the pixels never leave the GPU at all

Building

cargo build --release
cargo test          # grid geometry, ellipsising, glyph output

4.2 KiB Raw Blame History