A volume and brightness OSD

A pill near the bottom of the screen that shows the volume or the screen brightness when either changes, and fades away a moment after you stop. It never shows when you log in or save a file. The guide's level 4 explains each line.

#The file

// osd.strand. Media keys stay in the compositor: strand set audio.sink.volume +5%
enum Kind { volume, brightness }
state kind = volume
state shown = false
on change audio.sink.volume, audio.sink.muted { kind = volume; shown = true }
on change brightness.level                    { kind = brightness; shown = true }
on change audio.sink.volume, audio.sink.muted, brightness.level after 1.2s { shown = false }
let level = kind == volume ? (audio.sink.muted ? 0 : audio.sink.volume) : brightness.level

osd Level {                                       // focused monitor, overlay, click-through
  anchor: bottom; margin: 0, 0, 96; open: shown
  enter { opacity: 0; scale: 0.9 }
  row { width: 260; pad: $space.3; gap: $space.3; align: center
        radius: full; bg: $surface.alpha(0.8); blur: 24; shadow: $elevation.lg
    icon kind == volume ? audio.sink.icon : "display-brightness-symbolic" { size: 20 }
    meter level { grow: 1; height: 6; color: $accent; track: $fg.alpha(0.15) }
    text pct(level) { width: 4ch; align: end; font: $font.mono }
  }
}

#Bind the keys

Strand does not grab keys: your compositor keeps them and runs strand set. These are the commands for the volume and brightness keys:

strand set audio.sink.volume +5%
strand set audio.sink.volume -5%
strand set brightness.level +5%
strand set brightness.level -5%

Bind them to the keys in your compositor, so they work while the screen is locked and repeat while held (how: Start it and bind keys). On a service field, a signed number or percentage is a step from the value it has now, and it never goes below 0.

#What it looks like

The volume steps up three times, a few frames apart, as a held key does. The OSD springs in at the first change, follows the level, and fades out 1.2 seconds after the last one.

#How it works

• osd Level { … } is on the focused monitor, above everything, and clicks pass through it to what is underneath. It shows while open: is true.
• on change a, b { … } runs when a watched value changes, from anywhere: your keys, a slider, another program. It never runs for the first value, nor for a value a reload writes, nor when audio.sink becomes another device because the default output changed: the new device's volume is only the new baseline. That is why the OSD stays hidden when the shell starts, when you save a file and when the default output changes.
• on change … after 1.2s waits for quiet: it runs once, 1.2 seconds after the last change, so holding a key keeps the OSD up.
• let level follows whichever value changed last, and 0 while the output is muted.
• meter level fills from 0 to 1, and text pct(level) shows it as a percentage in a fixed-width font, 4ch wide, so the digits do not jump.

#Variations

• Several values in one place. Past two choices, a match reads better than nested ? and :; the guide shows the same OSD with match.
• Rolling digits. roll: true on the text rolls the digits when the number changes.
• On every monitor. screens: all on the osd puts a copy on each monitor, with screen in scope in each.