Workspaces widget: show what the other monitors are showing (and which way they are)

[zc0rp10]

Update (Sep 30): I first worked out the direction relative to the focused monitor. That broke on three screens: from the leftmost one, the middle and right screens both showed as "to the right". Each monitor now gets a fixed slot based on where it sits in the whole layout, so an icon means the same thing whichever screen you're on. With two monitors both approaches give the same result, so the screenshots below still apply.

On a multi-monitor setup the workspaces widget only marks the focused workspace. When I want to jump to a window on another screen, I can't tell from the bar which workspace that screen is showing. I either have to look over at it or guess.

Suggestion: mark the workspace that's visible on each other monitor with a partly filled square. The filled part shows where that monitor sits in your layout:

• ■ focused workspace (unchanged)
• two side by side: left / right half filled
• laptop below an external: top / bottom half filled
• three in a row: left / middle / right third filled
• numbers: everything else (unchanged)

Each monitor keeps its slot whichever screen you're on, so you learn that "middle third" = the middle screen.

How it works: monitors whose horizontal spans overlap share a column, and overlapping vertical spans share a row, so any layout becomes a small grid (three in a row = 3×1, laptop under an external = 1×2, two externals with a laptop under one = 2×2). The square is split into that grid and the monitor's cell is filled. It's drawn in QML (rounded outline plus a clipped fill) and snapped to whole physical pixels, so it stays crisp and matches the rounded square exactly at fractional scales.

Some Quickshell quirks I ran into, for whoever implements it:

• HyprlandMonitor.focused is never true (Quickshell 0.3.1). Hyprland.focusedMonitor works.
• Right after the shell starts, focusedWorkspace/focusedMonitor, each monitor's activeWorkspace and its position are null or wrong until the first workspace event. That also affects the stock widget: after a shell restart it shows no focused workspace until you switch. Reading hyprctl -j monitors once at startup covers it.
• monitor.activeWorkspace goes stale when a workspace is moved to another monitor, and after a runtime layout change. Calling Hyprland.refreshMonitors() on moveworkspacev2 / configreloaded / monitoraddedv2 / monitorremovedv2, and when the widget is created (the shell rebuilds the bar on layout changes), fixes both.
• Screen.devicePixelRatio reports 2 on a 1.25-scaled output; the window's devicePixelRatio is correct.

It's event-driven with no timers or polling, so there's no idle cost. I've been running it as a cloned workspaces plugin and I'm happy to open a PR against shell/plugins/bar/widgets/Workspaces.qml if this sounds good.

Related: #12810 tackles the same multi-monitor problem differently (per-monitor filtering). This keeps all workspaces on every bar but shows where each visible one lives.