Detent knob

pnpm add cn

/*
 * Bevel foundation. Every component builds on these tokens and utilities;
 * component stylesheets only add their own palettes and shapes.
 *
 * Layers:
 *   1. Light     one source, above and slightly in front of the screen.
 *   2. Depth     named elevations built from the light: recessed, flush,
 *                raised, pressed, object.
 *   3. Material  a surface recipe (leather, plastic, metal) that reads
 *                --bevel-material and --bevel-material-edge.
 *   4. Motion    two curves, a spring, and durations named by purpose.
 *   5. Shape     radii, stitching, and the type scale for amounts.
 */

:root {
  /* 1. Light */
  --bevel-highlight: oklch(1 0 0 / 0.22);
  --bevel-highlight-strong: oklch(1 0 0 / 0.35);
  --bevel-shade: oklch(0 0 0 / 0.32);
  --bevel-shade-strong: oklch(0 0 0 / 0.5);
  --bevel-cast: oklch(0.25 0.03 50 / 0.22);
  /* Stamped into a surface: shaded on the upper inner edge, lit below. */
  --bevel-deboss: 0 -1px 0 oklch(0 0 0 / 0.45), 0 1px 0 oklch(1 0 0 / 0.12);

  /* 3. Material defaults; components and variants override these. */
  --bevel-material: oklch(0.47 0.085 52);
  --bevel-material-edge: oklch(0.3 0.06 44);
  --bevel-material-recess: oklch(0.2 0.008 260); /* neutral dark; materials set their own */
  --bevel-grain: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='180' height='180'%3E%3Cfilter id='g'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.7' numOctaves='3' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .7 0 0 0 0'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23g)'/%3E%3C/svg%3E");
  --bevel-grain-size: 180px;

  /* 2. Depth */
  --bevel-depth-recessed:
    inset 0 1px 2px var(--bevel-shade-strong),
    0 1px 0 var(--bevel-highlight);
  --bevel-depth-flush:
    inset 0 1px 0 var(--bevel-highlight),
    inset 0 -1px 0 var(--bevel-shade);
  --bevel-depth-raised:
    inset 0 1px 0 var(--bevel-highlight),
    0 1px 0 var(--bevel-material-edge),
    0 2px 0 var(--bevel-material-edge),
    0 3px 5px var(--bevel-shade);
  --bevel-depth-pressed:
    inset 0 1px 2px var(--bevel-shade),
    0 1px 0 var(--bevel-highlight);
  /* A whole object resting on the page. */
  --bevel-depth-object:
    inset 0 1px 0 var(--bevel-highlight),
    inset 0 -1px 0 var(--bevel-shade),
    0 0 0 1px var(--bevel-material-edge),
    0 1px 1px var(--bevel-cast),
    0 6px 12px -2px var(--bevel-cast),
    0 18px 32px -8px var(--bevel-cast);
  /* The shadow under a loose object, for filter: drop-shadow(). */
  --bevel-depth-cast-sm: 0 4px 6px var(--bevel-cast);
  /* A thin object (a card) lying on another surface. */
  --bevel-depth-sheet:
    inset 0 1px 0 var(--bevel-highlight-strong),
    inset 0 0 0 1px oklch(0 0 0 / 0.12),
    0 -1px 2px oklch(0 0 0 / 0.18);

  /* 4. Motion */
  --bevel-ease-out: cubic-bezier(0.23, 1, 0.32, 1);
  --bevel-ease-in-out: cubic-bezier(0.77, 0, 0.175, 1);
  /* Underdamped spring, ~8% overshoot. Pure CSS; pair with --bevel-duration-move or longer. */
  --bevel-ease-spring: linear(0, 0.06, 0.202, 0.38, 0.561, 0.723, 0.856, 0.955, 1.023, 1.062, 1.081, 1.083, 1.075, 1.062, 1.047, 1.032, 1.019, 1.009, 1.002, 0.997, 0.994, 0.993, 0.993, 0.994, 1);
  --bevel-duration-press: 100ms; /* a control giving under a finger */
  --bevel-duration-small: 200ms; /* hover lifts, tabs, small state changes */
  --bevel-duration-move: 300ms; /* objects moving: cards, drawers */
  --bevel-duration-ambient: 520ms; /* whole-scene changes: lighting */
  --bevel-stagger: 30ms;
  --bevel-lift: 3px; /* how far an object rises on hover */
  --bevel-perspective: 30rem; /* viewing distance for parts that turn in 3D (covers, flaps) */
  /* Unchosen items in a group sit back in shadow. */
  --bevel-dim: 0.82;

  /* 5. Shape */
  --bevel-radius-xs: 0.25rem;
  --bevel-radius-sm: 0.5rem;
  --bevel-radius-md: 0.625rem;
  --bevel-radius-lg: 1rem;
  --bevel-radius-xl: 1.5rem;
  --bevel-stitch-width: 1.5px;
  --bevel-stitch-inset: 0.375rem;
  /* Amounts: the figure, its secondary parts (currency, cents), labels, fine print. */
  --bevel-amount: 2.25rem;
  --bevel-amount-minor: 1.25rem;
  --bevel-label: 0.75rem;
  --bevel-fine: 0.6875rem;
  --bevel-tracking-label: 0.08em; /* stamped labels */
  --bevel-tracking-print: 0.06em; /* printed marks on cards */

  /* Paper and ink */
  --bevel-paper: oklch(0.975 0.008 85);
  --bevel-paper-foreground: oklch(0.28 0.02 260);
  --bevel-paper-muted: oklch(0.48 0.015 260);
  --bevel-paper-rule: oklch(0.78 0.04 240 / 0.45);
  --bevel-paper-margin: oklch(0.68 0.14 25 / 0.45);
  --bevel-fibre: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='240' height='240'%3E%3Cfilter id='f'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.9 .35' numOctaves='2' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .18 0 0 0 0'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23f)'/%3E%3C/svg%3E");
  /* Ink soaks unevenly: mostly solid with pale specks. Used as a mask. */
  --bevel-ink-texture: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='160' height='160'%3E%3Cfilter id='i'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.85' numOctaves='2' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -2.4 0 0 0 2.1'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23i)'/%3E%3C/svg%3E");
  --bevel-ink-red: oklch(0.52 0.19 27);
  --bevel-ink-blue: oklch(0.44 0.14 262);
  --bevel-ink-green: oklch(0.5 0.12 155);
  --bevel-ink-black: oklch(0.3 0.01 260);
  --bevel-ink-amber: oklch(0.55 0.13 65);

  /* Brass and ivory: instrument hardware and dial faces */
  --bevel-brass: oklch(0.76 0.11 82);
  --bevel-brass-edge: oklch(0.52 0.08 70);
  --bevel-ivory: oklch(0.95 0.025 90);
  --bevel-ivory-foreground: oklch(0.25 0.015 60);
  --bevel-needle: oklch(0.55 0.2 27);

  /* Desk stationery: legal pads, pens, pencils, exhibit stickers */
  --bevel-pad: oklch(0.95 0.075 98); /* yellow legal pad */
  --bevel-pad-foreground: oklch(0.27 0.03 255);
  --bevel-pad-rule: oklch(0.72 0.06 235 / 0.45);
  --bevel-pad-margin: oklch(0.62 0.16 25 / 0.55);
  --bevel-pen-red: oklch(0.52 0.2 27); /* correcting pen */
  --bevel-pen-blue: oklch(0.42 0.15 262); /* writing pen */
  --bevel-pencil: oklch(0.55 0.01 260); /* not written in ink yet */
  --bevel-sticker: oklch(0.9 0.12 95); /* exhibit sticker */
  --bevel-sticker-foreground: oklch(0.26 0.03 70);
  /* Handwriting. Bring a marker font (e.g. Permanent Marker) for the full effect; these are fallbacks. */
  --bevel-font-marker: "Permanent Marker", "Marker Felt", "Chalkboard SE", ui-rounded, "Arial Rounded MT Bold", system-ui, sans-serif;
}

.dark {
  --bevel-highlight: oklch(1 0 0 / 0.14);
  /* Paper under dim light, not inverted: it's still paper. */
  --bevel-paper: oklch(0.88 0.008 85);
  --bevel-ivory: oklch(0.86 0.022 90);
  --bevel-pad: oklch(0.86 0.07 98);
  --bevel-cast: oklch(0 0 0 / 0.55);
}

/* Depth */
@utility bevel-recessed {
  background-color: var(--bevel-material-recess);
  box-shadow: var(--bevel-depth-recessed);
}
@utility bevel-flush {
  box-shadow: var(--bevel-depth-flush);
}
@utility bevel-raised {
  background-color: color-mix(in oklch, var(--bevel-material), white 7%);
  background-image: linear-gradient(to bottom, var(--bevel-highlight), transparent 60%);
  box-shadow: var(--bevel-depth-raised);
}
@utility bevel-pressed {
  background-color: color-mix(in oklch, var(--bevel-material), black 4%);
  background-image: none;
  box-shadow: var(--bevel-depth-pressed);
}
@utility bevel-object {
  box-shadow: var(--bevel-depth-object);
}

/* Materials */
@utility bevel-leather {
  background-color: var(--bevel-material);
  background-image:
    var(--bevel-grain),
    linear-gradient(to bottom, var(--bevel-highlight), transparent 28%, transparent 72%, var(--bevel-shade));
  background-size: var(--bevel-grain-size) var(--bevel-grain-size), 100% 100%;
  background-blend-mode: soft-light, normal;
}
@utility bevel-plastic {
  background-color: var(--bevel-material);
  background-image:
    linear-gradient(115deg, var(--bevel-highlight-strong), transparent 40%),
    linear-gradient(to bottom, transparent 25%, oklch(0 0 0 / 0.45));
  box-shadow: var(--bevel-depth-sheet);
}
@utility bevel-metal {
  background-color: var(--bevel-material);
  background-image:
    linear-gradient(to bottom, var(--bevel-highlight-strong), transparent 45%, var(--bevel-shade) 100%),
    repeating-linear-gradient(90deg, oklch(1 0 0 / 0.06) 0 1px, transparent 1px 3px);
  box-shadow:
    inset 0 0 0 1px oklch(0 0 0 / 0.25),
    inset 0 1px 0 var(--bevel-highlight-strong);
}

/* Details */
@utility bevel-deboss {
  text-shadow: var(--bevel-deboss);
}
@utility bevel-stitch {
  border-color: var(--bevel-stitch, oklch(0.88 0.05 82 / 0.8));
  border-style: dashed;
  border-width: var(--bevel-stitch-width);
  filter: drop-shadow(0 1px 0 var(--bevel-shade));
}
/* A lit fill sitting in a recess (meters, progress). Colour from --bevel-fill. */
@utility bevel-fill {
  background-color: var(--bevel-fill);
  background-image: linear-gradient(to bottom, oklch(1 0 0 / 0.55), transparent 55%, oklch(0 0 0 / 0.18));
  box-shadow: 0 0 6px -1px var(--bevel-fill);
}
/* A small indicator light. Colour from --bevel-led. */
@utility bevel-led {
  background-color: var(--bevel-led);
  background-image: radial-gradient(circle at 35% 30%, oklch(1 0 0 / 0.85), transparent 45%);
  box-shadow:
    0 0 6px var(--bevel-led),
    inset 0 -1px 1px oklch(0 0 0 / 0.35),
    0 1px 0 var(--bevel-highlight);
}

/* Paper: a sheet resting on the surface, with fibre in it. */
@utility bevel-paper {
  background-color: var(--bevel-paper);
  background-image: var(--bevel-fibre);
  background-size: 240px 240px;
  color: var(--bevel-paper-foreground);
  box-shadow:
    0 1px 1px var(--bevel-cast),
    0 6px 14px -4px var(--bevel-cast);
}
/* Ink on paper: multiplies into the surface and soaks unevenly. Colour from --bevel-ink. */
@utility bevel-ink {
  color: var(--bevel-ink, var(--bevel-ink-red));
  border-color: currentColor;
  mix-blend-mode: multiply;
  mask-image: var(--bevel-ink-texture);
  mask-size: 160px 160px;
}
/* Glass over an instrument window: one reflection from the light above. Put on an overlay element. */
@utility bevel-glass {
  pointer-events: none;
  background-image: linear-gradient(165deg, var(--bevel-highlight-strong) 0%, transparent 38%, transparent 70%, var(--bevel-shade) 100%);
}

/* Material families: one per screen. Set on the screen's container. */
[data-bevel-family="leather"] {
  --bevel-cast: oklch(0.25 0.03 50 / 0.22);
}
[data-bevel-family="paper"] {
  --bevel-cast: oklch(0.3 0.01 250 / 0.16);
}
.dark :is([data-bevel-family="leather"], [data-bevel-family="paper"]) {
  --bevel-cast: oklch(0 0 0 / 0.55);
}

/*
 * Ruled paper: rules every --bevel-rule-height and a margin line at
 * --bevel-rule-margin. Set --bevel-sheet for the paper colour. The ruling
 * scrolls with the content.
 */
@utility bevel-ruled {
  background-color: var(--bevel-sheet, var(--bevel-paper));
  background-image:
    linear-gradient(
      to right,
      transparent calc(var(--bevel-rule-margin) - 1px),
      var(--bevel-sheet-margin, var(--bevel-paper-margin)) calc(var(--bevel-rule-margin) - 1px) calc(var(--bevel-rule-margin) + 1px),
      transparent calc(var(--bevel-rule-margin) + 1px)
    ),
    repeating-linear-gradient(
      to bottom,
      transparent 0 calc(var(--bevel-rule-height) - 1px),
      var(--bevel-sheet-rule, var(--bevel-paper-rule)) calc(var(--bevel-rule-height) - 1px) var(--bevel-rule-height)
    ),
    var(--bevel-fibre);
  background-size: 100% 100%, 100% 100%, 240px 240px;
  background-attachment: local;
  color: var(--bevel-paper-foreground);
  box-shadow:
    0 1px 1px var(--bevel-cast),
    0 6px 14px -4px var(--bevel-cast);
}

"use client"

import * as React from "react"
import { cn } from "cn"

type Stop = { value: string; label: string }

type DetentKnobContextValue = {
  register: (stop: Stop) => () => void
}

const DetentKnobContext = React.createContext<DetentKnobContextValue | null>(null)

/* Positions spread over 270°, from bottom-left to bottom-right, like a range switch. */
const SWEEP = 270

function angleAt(index: number, count: number) {
  return count < 2 ? 0 : -SWEEP / 2 + (SWEEP * index) / (count - 1)
}

type DetentKnobProps = Omit<React.ComponentProps<"div">, "onChange" | "defaultValue"> & {
  value?: string
  defaultValue?: string
  onValueChange?: (value: string) => void
  disabled?: boolean
}

/**
 * A rotary switch: it clicks into fixed positions and stops hard at both
 * ends. Turn it with arrow keys, Home and End, or drag it round. List the
 * positions as DetentKnobStop children. Give it an aria-label.
 */
function DetentKnob({
  className,
  value: valueProp,
  defaultValue,
  onValueChange,
  disabled,
  children,
  ...props
}: DetentKnobProps) {
  const [stops, setStops] = React.useState<Stop[]>([])
  const [uncontrolled, setUncontrolled] = React.useState(defaultValue)
  const [bump, setBump] = React.useState<{ dir: "up" | "down"; n: number } | null>(null)
  const knob = React.useRef<HTMLDivElement>(null)
  const value = valueProp ?? uncontrolled ?? stops[0]?.value
  const index = Math.max(0, stops.findIndex((s) => s.value === value))

  const register = React.useCallback((stop: Stop) => {
    // Stops keep the order they mounted in, which is their order round the dial.
    setStops((all) =>
      all.some((s) => s.value === stop.value)
        ? all.map((s) => (s.value === stop.value ? stop : s))
        : [...all, stop]
    )
    return () => setStops((all) => all.filter((s) => s.value !== stop.value))
  }, [])
  const context = React.useMemo(() => ({ register }), [register])

  const select = (next: number) => {
    if (disabled || !stops.length) return
    if (next < 0 || next > stops.length - 1) {
      setBump((b) => ({ dir: next < 0 ? "down" : "up", n: (b?.n ?? 0) + 1 }))
      return
    }
    if (next === index) return
    const stop = stops[next]!
    setUncontrolled(stop.value)
    onValueChange?.(stop.value)
  }

  const onKeyDown = (event: React.KeyboardEvent) => {
    const step: Record<string, number> = { ArrowRight: 1, ArrowUp: 1, ArrowLeft: -1, ArrowDown: -1 }
    if (event.key in step) select(index + step[event.key]!)
    else if (event.key === "Home") select(0)
    else if (event.key === "End") select(stops.length - 1)
    else return
    event.preventDefault()
  }

  // Dragging: the nearest position to the pointer's angle round the centre.
  const fromPointer = (event: React.PointerEvent) => {
    const box = knob.current?.getBoundingClientRect()
    if (!box || stops.length < 2) return
    const x = event.clientX - (box.left + box.width / 2)
    const y = event.clientY - (box.top + box.height / 2)
    const angle = (Math.atan2(x, -y) * 180) / Math.PI
    const t = (angle + SWEEP / 2) / SWEEP
    if (t < -0.05 || t > 1.05) return // in the dead zone at the bottom: stay put
    select(Math.min(stops.length - 1, Math.max(0, Math.round(t * (stops.length - 1)))))
  }

  const current = stops[index]
  return (
    <DetentKnobContext value={context}>
      {children}
      <div
        data-slot="detent-knob"
        data-disabled={disabled ? "" : undefined}
        className={cn("relative grid size-56 shrink-0 place-items-center select-none data-disabled:opacity-50", className)}
      >
        {stops.map((stop, i) => (
          <span
            key={stop.value}
            aria-hidden
            data-selected={i === index ? "" : undefined}
            onClick={() => select(i)}
            className="absolute top-1/2 left-1/2 cursor-pointer text-xs font-semibold whitespace-nowrap text-muted-foreground transition-colors duration-(--bevel-duration-small) data-selected:text-foreground motion-reduce:transition-none"
            style={{
              transform: `translate(-50%, -50%) rotate(${angleAt(i, stops.length)}deg) translateY(calc(var(--detent-knob-label-radius) * -1)) rotate(${-angleAt(i, stops.length)}deg)`,
            }}
          >
            {stop.label}
          </span>
        ))}
        <div
          ref={knob}
          role="slider"
          tabIndex={disabled ? -1 : 0}
          aria-disabled={disabled || undefined}
          aria-valuemin={0}
          aria-valuemax={Math.max(0, stops.length - 1)}
          aria-valuenow={index}
          aria-valuetext={current ? `${current.label}, ${index + 1} of ${stops.length}` : undefined}
          aria-orientation="horizontal"
          onKeyDown={onKeyDown}
          onPointerDown={(event) => {
            if (disabled) return
            event.currentTarget.setPointerCapture(event.pointerId)
            fromPointer(event)
          }}
          onPointerMove={(event) => {
            if (event.currentTarget.hasPointerCapture(event.pointerId)) fromPointer(event)
          }}
          className="group size-32 touch-none rounded-full outline-none"
          {...props}
        >
          <div
            key={bump?.n ?? 0}
            data-slot="detent-knob-body"
            data-bump={bump?.dir}
            className={cn("size-full rounded-full", bump && "detent-knob-bump motion-reduce:animate-none")}
          >
            <div
              data-slot="detent-knob-cap"
              className={cn(
                "bevel-metal relative size-full rounded-full shadow-(--bevel-depth-object)",
                "transition-[rotate] duration-(--bevel-duration-small) ease-(--bevel-ease-spring) motion-reduce:transition-none",
                "group-focus-visible:ring-3 group-focus-visible:ring-ring/60"
              )}
              style={{ rotate: `${angleAt(index, stops.length)}deg` }}
            >
              <span aria-hidden className="detent-knob-knurl absolute inset-0 rounded-full" />
              <span aria-hidden className="bevel-metal absolute inset-3 rounded-full shadow-(--bevel-depth-raised)" />
              <span
                aria-hidden
                className="absolute top-3 left-1/2 h-8 w-1 -translate-x-1/2 rounded-full bg-(--detent-knob-pointer)"
              />
            </div>
          </div>
        </div>
      </div>
    </DetentKnobContext>
  )
}

type DetentKnobStopProps = { value: string; children: string }

/** One position. Renders nothing itself: the knob draws its label round the dial. */
function DetentKnobStop({ value, children }: DetentKnobStopProps) {
  const context = React.useContext(DetentKnobContext)
  if (!context) throw new Error("DetentKnobStop must be inside <DetentKnob>")
  const { register } = context
  React.useEffect(() => register({ value, label: children }), [value, children, register])
  return null
}

export { DetentKnob, DetentKnobStop }
export type { DetentKnobProps, DetentKnobStopProps }

/*
 * Detent knob: a rotary switch that clicks into fixed positions and stops
 * hard at both ends. Builds on bevel.css (metal, raised, motion).
 */

:root {
  --detent-knob-cap: oklch(0.3 0.01 260); /* knurled black cap */
  --detent-knob-cap-edge: oklch(0.18 0.01 260);
  --detent-knob-pointer: oklch(0.95 0.02 90);
  --detent-knob-active: oklch(0.82 0.15 85);
  --detent-knob-label-radius: 5.5rem; /* centre to label */
  --detent-knob-bump: 4deg; /* how far it gives at an endstop */
}

[data-slot="detent-knob-cap"] {
  --bevel-material: var(--detent-knob-cap);
  --bevel-material-edge: var(--detent-knob-cap-edge);
}

/* Knurling: fine ridges around the cap's edge. */
@utility detent-knob-knurl {
  background-image: repeating-conic-gradient(var(--bevel-highlight) 0deg 3deg, var(--bevel-shade) 3deg 6deg);
}

/* Pushing past an endstop: it gives a little and springs back. */
@keyframes detent-knob-bump {
  40% {
    rotate: var(--detent-knob-bump-to);
  }
}
[data-slot="detent-knob-body"][data-bump="up"] {
  --detent-knob-bump-to: var(--detent-knob-bump);
}
[data-slot="detent-knob-body"][data-bump="down"] {
  --detent-knob-bump-to: calc(var(--detent-knob-bump) * -1);
}
@utility detent-knob-bump {
  animation: detent-knob-bump var(--bevel-duration-small) var(--bevel-ease-out);
}

@import "./bevel.css";
@import "./detent-knob.css";