Milad Alizadeh
5b1f0f74e8
Displays are capture sources too — ext-image-capture-source-v1 makes one
from a wl_output just as it does from a toplevel handle — so they are now
tiles as well, appended after the windows and labelled "NAME · display".
They are snapshot-only: a live display tile contains this overlay, which
contains the display tile, and refreshing that never settles while
costing a whole screen per frame. They also only get one buffer for the
same reason, which is worth ~29MB here.
The bigger change is what wlgrid reports. It was focusing the pick itself
and printing only under --print, which suits a keybinding and nothing
else. Now it is a chooser: it always reports the pick, never acts unless
asked (--focus), exits 1 when cancelled, and can say it three ways.
--format portal emits what xdg-desktop-portal-wlr's simple chooser reads
("Monitor: NAME" / "Window: <foreign-toplevel identifier>"), so wlgrid
can be the picker behind getDisplayMedia, with live previews of windows
and displays. That contract is also why tsv carries both identifiers: the
portal and grim -T want the toplevel identifier, sway scripting wants the
con_id. --format json gives the whole record for jq.
Navigation also takes hjkl, and --help now describes every flag with its
default plus the output formats.
159 lines
6.9 KiB
Markdown
159 lines
6.9 KiB
Markdown
# wlgrid
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A window switcher for wlroots compositors: a grid overlay of **live** window
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previews that looks like a rofi theme, and focuses the window you pick.
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It replaces a `wlthumbs | rofi` pipeline, and doubles as a screencast source
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picker for the desktop portal. The difference is that no thumbnails
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exist: each window is captured straight into a `wl_shm` buffer that is handed to
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its own `wl_subsurface`, and `wp_viewporter` tells the compositor which rectangle
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to scale it into. There is no image encoding, no scaler, and no full-resolution
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bitmap in this process — which is also why it appears in about 60 ms and holds
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~18 MB of RSS however many windows are open.
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```
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sway-tree 0.6ms window list + con_ids over sway IPC
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toplevels 0.2ms ext-foreign-toplevel-list handles
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constraints 1.5ms every capture session's buffer size, in one roundtrip
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capture 52.5ms 8 windows, all frames in flight at once
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labels 0.0ms shaped on a worker thread while the captures ran
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mapped 4.9ms layer surface + subsurfaces on screen
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```
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The capture phase is the compositor reading full-resolution window pixels out of
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the GPU. It is bandwidth-bound (~1.1 GB/s here) and unaffected by how large the
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thumbnails are — which also makes it a free window to do other work in. Loading
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a font and rasterising its first glyphs costs ~20ms, so labels are shaped on a
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worker thread started before the captures and joined after them, and cost
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nothing in wall clock.
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## Status
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Working: a labelled grid of live previews with keyboard navigation. Type-to-filter
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is the one thing the rofi version had that this doesn't — see the roadmap.
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## Usage
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```
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wlgrid [--print] [--verbose] [--hide-labels] [--font FAMILY] [--font-size PX]
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[--live all|current|none] [--fps N] [--timeout SECS]
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```
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- `--print` writes the selected sway `con_id` to stdout instead of focusing it
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- `--verbose` prints phase timings and how many windows were captured
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- `--hide-labels` draws an icon-only grid
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- `--font FAMILY` label font family (default `Berkeley Mono`)
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- `--font-size PX` label size in logical px
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- `--live all|current|none` which tiles keep updating (default `all`)
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- `--fps N` cap on updates per tile per second (default 12)
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- `--timeout SECS` exits after a deadline (an escape hatch: the overlay takes an
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exclusive keyboard grab)
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wlgrid is a chooser: it reports what you picked and leaves acting on it to the
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caller. The pick goes to stdout, nothing does if you cancel, and the exit status
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is 0 for a pick and 1 for a cancel.
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```sh
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# sway scripting: act on the con_id
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swaymsg "[con_id=$(wlgrid | cut -f2)] focus"
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# or let wlgrid do it, for a bare keybinding
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bindsym $mod+Tab exec wlgrid --focus
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```
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Three formats, because the identifiers different consumers need differ:
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| `--format` | output |
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| `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 |
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| `json` | the same record with every key always present, for `jq` |
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| `portal` | `Monitor: NAME` or `Window: TOPLEVEL_ID` |
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`portal` is exactly what xdg-desktop-portal-wlr's `simple` chooser reads, so
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wlgrid can be the picker for `getDisplayMedia` and friends — with live previews
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of both windows and displays:
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```ini
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[screencast]
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chooser_type=simple
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chooser_cmd=wlgrid --format portal
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```
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| key | |
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| `→` `←` / `l` `h` / `Tab` `Shift+Tab` | next / previous tile |
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| `↓` `↑` / `j` `k` | move a row |
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| `Home` `End` | first / last |
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| `Enter` | pick |
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| `Escape` / `q` | cancel |
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Navigation reads raw evdev keycodes, so it is layout-independent — but it also
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means virtual-keyboard clients such as `wtype` (which invent their own keymap)
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cannot drive it. That goes away with xkb support, which filtering needs anyway.
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## Live previews
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Capture sessions stay open, so a tile can be refreshed. Three things keep that
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from being expensive:
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- **It is damage-driven.** After a session's first frame the compositor only
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produces another once the window content changes, so a request left
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outstanding on an idle window costs nothing. Measured over 4s with one
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animating window out of ten: `52,52,1,1,1,1,1,1,13,1` frames — the static
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windows delivered exactly their first frame and nothing more.
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- **Frame callbacks are the clock.** Re-captures are driven by the overlay's own
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`wl_surface.frame` callbacks, so they stop when it isn't being presented, and
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`--fps` throttles per tile on top of that (12 fps measured as 12.1).
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- **Two buffers per window, alternating.** A capture must not write into a buffer
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the compositor is reading, so each window gets two and `wl_buffer.release`
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decides which is free. Note that release is the entire contract: with `wl_shm`
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the compositor copies the pixels out at commit and hands the buffer straight
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back, so the slot on screen is usually free too — waiting for it to stop being
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displayed instead deadlocks after two frames.
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The cost is memory and bandwidth: two full-resolution buffers per window (110 MB
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of shm for ten windows on this display, versus 55 MB with `--live none`) and a
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readback per refreshed frame. `--live current` refreshes only the selected tile,
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which is much cheaper and still reads as alive.
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## Look
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Colours, font metrics and grid geometry come from the rofi theme this replaces
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(gruvbox dark, a yellow selection filling the element padding, `ceil(sqrt(n))`
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columns capped at 4, 16:9 tiles, `title · app` centred underneath) and live in
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`src/theme.rs`. They will move to a config file so they can't drift from the
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`.rasi`.
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The font is looked up by family name. Your own font directories are scanned
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first because they are small; the full system scan (~37ms) happens only if the
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family isn't found there, and an unknown family then falls back to whatever
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cosmic-text picks rather than failing. Long titles are ellipsised to the cell.
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## Requirements
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A wlroots compositor advertising `ext-image-copy-capture-v1`,
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`ext-image-capture-source-v1` (with the foreign-toplevel source manager),
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`ext-foreign-toplevel-list-v1`, `wlr-layer-shell-unstable-v1` and
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`wp_viewporter` — sway 1.11+, and in principle Hyprland, labwc and jay, though
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only sway is tested. sway is also the source of truth for the window list and
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for focusing, over its IPC socket.
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Known upstream issue: holding per-toplevel capture sessions open makes windows
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blurry on **fractionally scaled** outputs
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([sway#9113](https://github.com/swaywm/sway/issues/9113)). Integer scales are
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unaffected. It matters more once previews are live.
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## Roadmap
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- type-to-filter with fzf-quality fuzzy matching (and the xkb keyboard input it
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needs, which would also let virtual-keyboard clients drive the overlay)
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- dmabuf capture, so the pixels never leave the GPU at all — and live previews
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stop costing a readback per frame
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## Building
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```
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cargo build --release
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cargo test # grid geometry, ellipsising, glyph output
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```
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