Show a Reverb node as a device with a round screen of its tail (#389)

The Compressor, the Gain, the Chip and the Envelope are devices in the
graph. The Reverb was still a list of rows, and how long and how dark
its tail rings was left to the numbers.

- The node is a plate of 640x280 in pale lavender. Its inputs are on
  the left, its output on the right.
- A round screen draws the tail as rings out from the sound. A ring's
  radius is its time, as the root of its seconds, on one scale up to
  10.5 s for every Reverb. So a Room is a small disc and a Cave fills
  two thirds.
- A ring is as bright as the tail is loud there, evenly in dB. Its
  colour is how much of the highs is left, from ice to violet, with
  the cut-off of the impulse response (reverbCutoff, now shared).
- The pre-delay is a dark gap round the dot, a dashed ring marks
  -60 dB. Seeded dots stand for the reflections. Wet fades the tail
  against the dot.
- A type of Sound draws the peaks of its sound from the library, each
  against its loudest. It says LOADING until they are there.
- A button for each type, a list of the sounds and four chrome knobs:
  Decay, Damping, Pre-delay and Wet.
- A knob the type does not take is greyed but turns. It goes over to
  Custom with the type's numbers, as one undo step. Picking a sound
  makes the type Sound, also one step.
- NodeParamDrag can write several settings as one drag for that.
- Test hook __gm.reverb.panel(nodeId), for the sound FX and the
  instrument graph.

Tests:
- Unit reverb-view: 10 new tests for the plate, the knob turn, the
  numbers per type, the scale, the tail and the texts. A screen that
  ignores damping turns the highs test red.
- e2e 34 (atx): 1 new check (device between its ports, decay knob of
  a Hall goes to Custom as one undo step, Cave button, a sound from
  the list makes it Sound and draws that sound).
- Probe pictures on stein2: Room, Hall, Cave, Plate, Custom with
  damping 1 and pre-delay 0.3 s, Sound.
- Gate (atx): CHECK EXIT 0, 287 files, 4393 tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/core/soundfx/nodes.ts

@@ -1244,7 +1244,17 @@ const REVERB_DAMPING = { ...numberRow('damping', 'Damping', 0, 1, 0.01), default
 const PREDELAY = { ...numberRow('predelay', 'Pre-delay (s)', 0, 0.5, 0.001), default: 0.01 };
 const REVERB_MIX = { ...numberRow('mix', 'Wet', 0, 1, 0.01), default: 0.3 };
 
-function reverbRoomOf(settings: PropertyBag): ReverbRoom {
+/** The numbers of a Reverb, for its device (#389). */
+export const REVERB_ROWS = {
+  decay: REVERB_DECAY,
+  damping: REVERB_DAMPING,
+  predelay: PREDELAY,
+  mix: REVERB_MIX,
+};
+export const REVERB_ROOM_KEY = REVERB_ROOM.key;
+export const REVERB_IMPULSE_KEY = IMPULSE.key;
+
+export function reverbRoomOf(settings: PropertyBag): ReverbRoom {
   return REVERB_ROOMS.find((option) => option.value === settings[REVERB_ROOM.key])?.value ?? 'room';
 }
 

src/core/soundfx/reverb.ts

@@ -32,11 +32,19 @@ export const REVERB_PRESETS: Record<'room' | 'hall' | 'cave' | 'plate', ReverbSh
 export const REVERB_MAX_DECAY = 10;
 
 /** Where the highs of a fully damped tail have fallen to by its end, and an undamped one stays. */
-const OPEN_HZ = 20000;
-const DAMPED_HZ = 500;
+export const OPEN_HZ = 20000;
+export const DAMPED_HZ = 500;
 
-/** A small, fast generator, so every voice gets the same noise and a check the same numbers. */
-function noise(seed: number): () => number {
+/** Where the highs of a tail are cut `share` of the way through it, 0 to 1, at this damping. */
+export function reverbCutoff(damping: number, share: number): number {
+  return OPEN_HZ * (DAMPED_HZ / OPEN_HZ) ** (Math.max(0, Math.min(1, damping)) * share);
+}
+
+/**
+ * A small, fast generator, so every voice gets the same noise and a check the same numbers; the
+ * Reverb's device (#389) scatters its reflections with it.
+ */
+export function seededNoise(seed: number): () => number {
   let state = seed >>> 0;
   return () => {
     state = (state + 0x6d2b79f5) >>> 0;
@@ -54,14 +62,13 @@ function noise(seed: number): () => number {
  */
 export function reverbImpulse(sampleRate: number, decay: number, damping: number): Float32Array[] {
   const length = Math.max(1, Math.round(Math.min(REVERB_MAX_DECAY, Math.max(0.01, decay)) * sampleRate));
-  const shut = Math.max(0, Math.min(1, damping));
   return [1, 2].map((seed) => {
-    const next = noise(seed);
+    const next = seededNoise(seed);
     const out = new Float32Array(length);
     let low = 0;
     for (let i = 0; i < length; i++) {
       const t = i / length;
-      const cutoff = OPEN_HZ * (DAMPED_HZ / OPEN_HZ) ** (shut * t);
+      const cutoff = reverbCutoff(damping, t);
       const keep = Math.exp((-2 * Math.PI * cutoff) / sampleRate);
       low = (1 - keep) * next() + keep * low;
       out[i] = low * 10 ** (-3 * t);

src/editor/debug/graphHooks.ts

@@ -7,6 +7,7 @@ import { ChipPanel } from '../soundfx/ChipPanel';
 import { EnvelopePanel } from '../soundfx/EnvelopePanel';
 import { CompressorPanel } from '../soundfx/CompressorPanel';
 import { GainPanel } from '../soundfx/GainPanel';
+import { ReverbPanel } from '../soundfx/ReverbPanel';
 import { CurvePanel } from '../soundfx/CurvePanel';
 import type { EqEditor } from '../soundfx/EqEditor';
 import { rectOf } from '../textProbe';
@@ -366,6 +367,49 @@ export function graphHooks({ state, editor }: HookContext) {
         };
       },
     },
+    /**
+     * The panel a Reverb node shows (#389), in the sound FX graph or the instrument graph: whether it
+     * is shown and where, its knobs, which settings are idle, the picked type, the sound, what the
+     * screen draws and says, and the node's ports.
+     */
+    reverb: {
+      panel: (nodeId: string) => {
+        const canvas = [editor.soundFxEditor.canvas, editor.instrumentEditor.canvas].find(
+          (c) => c.faceOf(nodeId)?.widget instanceof ReverbPanel,
+        );
+        const panel = canvas?.faceOf(nodeId)?.widget;
+        if (!canvas || !(panel instanceof ReverbPanel)) return null;
+        const node = canvas.nodeScreen(nodeId);
+        const ports = (keys: string[], isOutput: boolean) =>
+          Object.fromEntries(keys.map((key) => [key, canvas.portGlobal(nodeId, key, isOutput)]));
+        return {
+          shown: shownOnScreen(panel),
+          rect: screenRect(panel),
+          size: { w: panel.w, h: panel.h },
+          node: node?.rect ?? null,
+          inputs: ports(node?.inputs ?? [], false),
+          outputs: ports(node?.outputs ?? [], true),
+          knobs: Object.fromEntries(
+            Object.entries(panel.knobs).map(([key, knob]) => [
+              key,
+              { value: knob.value, number: knob.shown, enabled: knob.enabled, dial: knob.dialGlobal() },
+            ]),
+          ),
+          idle: [...panel.idle],
+          room: panel.roomButtons.find((b) => b.picked)?.room ?? null,
+          rooms: Object.fromEntries(panel.roomButtons.map((b) => [b.room, screenCentre(b)])),
+          highs: panel.highs.text,
+          sound: { text: panel.soundButton.text, at: screenCentre(panel.soundButton) },
+          scope: {
+            /** How far out the tail ends, 0 to 1 of the outer ring; 0 without a tail. */
+            reach: panel.scope.reach,
+            rings: panel.scope.rings,
+            kind: panel.scope.tail?.kind ?? null,
+            says: panel.scope.says,
+          },
+        };
+      },
+    },
     instrument: {
       current: () => editor.instrumentEditor.currentAssetId,
       info: () => editor.instrumentEditor.shownInfo,

src/editor/soundfx/ReverbFace.ts

@@ -0,0 +1,145 @@
+import { oneStep } from '../../core/commands/CompoundCommand';
+import { SetNodeParamCommand } from '../../core/commands/graphCommands';
+import type { GraphNode } from '../../core/graph';
+import { findGraphAsset } from '../../core/model/Project';
+import { assetRefLabel, soundChoices } from '../../core/properties/assetRef';
+import { playedSoundById } from '../../core/properties/playedSound';
+import { REVERB_IMPULSE_KEY, REVERB_ROOM_KEY, SoundFxReverb } from '../../core/soundfx/nodes';
+import type { ReverbRoom } from '../../core/soundfx/reverb';
+import { Menu, type Widget } from '../../ui';
+import { soundLibrary } from '../../viewport/SoundLibrary';
+import type { NodeFace } from '../graph/nodeFace';
+import type { EditorState } from '../state';
+import { compressorWired } from './CompressorEditor';
+import { NodeParamDrag } from './nodeParamDrag';
+import { type ReverbHost, ReverbPanel } from './ReverbPanel';
+import {
+  customFrom,
+  idleReverbKeys,
+  type ReverbKey,
+  type ReverbTail,
+  reverbValues,
+  roomTakes,
+} from './reverbView';
+
+/**
+ * A Reverb node drawn as its device (#389): its tail drawn from its settings – or from the peaks of
+ * the sound it takes – every one of them worked right in the graph. A knob its type does not take
+ * goes over to Custom with the numbers the type had. It listens to nothing while the sound plays.
+ */
+export class ReverbFace implements NodeFace, ReverbHost {
+  readonly widget: ReverbPanel;
+  private readonly drag: NodeParamDrag;
+  /** Sounds whose peaks are on their way, so they are asked for once. */
+  private readonly loading = new Set<string>();
+
+  constructor(
+    private readonly state: EditorState,
+    private readonly assetId: string,
+    private readonly nodeId: string,
+  ) {
+    this.widget = new ReverbPanel(this);
+    this.drag = new NodeParamDrag(state, 'reverb-face');
+  }
+
+  private node(): GraphNode | null {
+    const node = findGraphAsset(this.state.project, this.assetId)?.graph.nodes.find(
+      (n) => n.id === this.nodeId,
+    );
+    return node?.type === SoundFxReverb.type ? node : null;
+  }
+
+  private wired = (key: string): boolean =>
+    compressorWired(this.state.project, this.assetId, this.nodeId, key);
+
+  sync(): void {
+    const node = this.node();
+    if (!node) return;
+    const values = reverbValues(node.params);
+    let tail: ReverbTail | null = null;
+    let missing = '';
+    if (values.room !== 'sound')
+      tail = { kind: 'made', predelay: values.predelay, decay: values.decay, damping: values.damping };
+    else {
+      const file = values.impulse ? playedSoundById(this.state.project, values.impulse) : '';
+      const peaks = file ? soundLibrary.peaks(file) : null;
+      const seconds = file ? soundLibrary.duration(file) : null;
+      if (peaks && seconds !== null) tail = { kind: 'sound', predelay: values.predelay, seconds, peaks };
+      else if (!file) missing = 'NO SOUND';
+      else if (soundLibrary.failedToLoad(file)) missing = 'CANNOT LOAD';
+      else {
+        missing = 'LOADING';
+        this.load(file);
+      }
+    }
+    this.widget.sync({
+      values,
+      wired: this.wired,
+      idle: idleReverbKeys(values.room),
+      tail,
+      sound: values.impulse ? assetRefLabel(this.state.project, values.impulse) : '',
+      missing,
+    });
+  }
+
+  /** Loads what the screen draws a sound's tail from, and draws it once it is there. */
+  private load(file: string): void {
+    if (this.loading.has(file)) return;
+    this.loading.add(file);
+    void soundLibrary.loadPicture(file).then(() => {
+      this.loading.delete(file);
+      this.sync();
+    });
+  }
+
+  tick(): boolean {
+    return false;
+  }
+
+  hide(): void {}
+
+  preview(key: ReverbKey, value: number): void {
+    const node = this.node();
+    if (!node) return;
+    // A knob the type does not take: Custom, from the numbers the knobs showed.
+    if (this.drag.holds(REVERB_ROOM_KEY) || !roomTakes(reverbValues(node.params).room, key))
+      this.drag.previewAll(node, customFrom(reverbValues(node.params), key, value));
+    else this.drag.preview(node, key, value);
+  }
+
+  commit(key: ReverbKey, value: number): void {
+    const node = this.node();
+    if (!node) return;
+    this.preview(key, value);
+    this.drag.commitHeld(this.assetId, node, 'Turn Reverb knob');
+  }
+
+  pickRoom(room: ReverbRoom): void {
+    const node = this.node();
+    if (node && reverbValues(node.params).room !== room)
+      this.state.execute(new SetNodeParamCommand(this.assetId, this.nodeId, REVERB_ROOM_KEY, room));
+  }
+
+  /** The sounds of the project; picking one makes it the impulse response and the type Sound. */
+  pickSound(button: Widget): void {
+    const node = this.node();
+    if (!node) return;
+    const values = reverbValues(node.params);
+    const items = soundChoices(this.state.project).map((sound) => ({
+      label: sound.label,
+      current: sound.id === values.impulse,
+      onSelect: () => {
+        const commands = [
+          ...(sound.id !== values.impulse
+            ? [new SetNodeParamCommand(this.assetId, this.nodeId, REVERB_IMPULSE_KEY, sound.id)]
+            : []),
+          ...(values.room !== 'sound'
+            ? [new SetNodeParamCommand(this.assetId, this.nodeId, REVERB_ROOM_KEY, 'sound')]
+            : []),
+        ];
+        if (commands.length > 0) this.state.execute(oneStep('Pick Reverb sound', commands));
+      },
+    }));
+    if (items.length > 0) new Menu(items, { searchable: true }).openBelow(button);
+  }
+}

src/editor/soundfx/ReverbPanel.ts

@@ -0,0 +1,413 @@
+/**
+ * The Reverb as a device (#389), what its node shows in the graph: the Compressor's plate (#379) in
+ * pale lavender, a round screen that draws the tail as rings out from the sound – as far out as it
+ * rings, as bright as it is loud, as blue as its highs are still there – a button for each type, the
+ * sound a type of Sound takes, and a chrome knob for each number.
+ */
+import { type FederatedPointerEvent, Graphics, type Text, type TextStyle } from 'pixi.js';
+import { REVERB_ROWS } from '../../core/soundfx/nodes';
+import { REVERB_ROOMS, type ReverbRoom } from '../../core/soundfx/reverb';
+import { mixColor } from '../../core/util/color';
+import { crispText, Dropdown, Knob, textStyle, Widget } from '../../ui';
+import { apartLabels } from './eqView';
+import { drawPlate, engrave, INK, placeEngraving, type PlateLook } from './CompressorPanel';
+import { type Box, KNOB_CAPTION } from './hardwareView';
+import {
+  markText,
+  REVERB_KEYS,
+  REVERB_KNOBS,
+  REVERB_LAYOUT,
+  REVERB_PANEL,
+  type ReverbKey,
+  type ReverbTail,
+  type ReverbValues,
+  reflections,
+  SCOPE_GRID,
+  SCOPE_MARKS,
+  scopeRadius,
+  scopeTexts,
+  tailRings,
+  tailSeconds,
+  wetShares,
+} from './reverbView';
+
+/** What the panel asks of the node it sits in. */
+export interface ReverbHost {
+  preview(key: ReverbKey, value: number): void;
+  commit(key: ReverbKey, value: number): void;
+  pickRoom(room: ReverbRoom): void;
+  /** Opens the sounds to pick from below the button. */
+  pickSound(button: Widget): void;
+}
+
+/** What the panel shows of a node. */
+export interface ReverbShown {
+  values: ReverbValues;
+  wired: (key: ReverbKey) => boolean;
+  /** The settings that do nothing as things stand. */
+  idle: ReadonlySet<ReverbKey | 'impulse'>;
+  /** The tail to draw; null while there is none to know – no sound picked, or not loaded yet. */
+  tail: ReverbTail | null;
+  /** The picked sound's name, '' for none. */
+  sound: string;
+  /** What the screen says where it has no tail. */
+  missing: string;
+}
+
+/** Pale anodised lavender. */
+const LAVENDER: PlateLook = {
+  stops: [
+    [0, 0xe2ddf2],
+    [0.5, 0xcdc6e8],
+    [1, 0xb0a7d6],
+  ],
+  rim: 0x7a70a6,
+  grain: 0x544a80,
+};
+const BEZEL = 0x2c2a3c;
+const BEZEL_TEXT = 0xc4bfe0;
+/** Night glass; a tail with its highs is ice, one that lost them violet. */
+const SCOPE = {
+  glass: 0x0b0d1a,
+  grid: 0x232a48,
+  text: 0x9fb0ff,
+  dim: 0x5b6590,
+  bright: 0xd8f6ff,
+  dull: 0x6c4fd0,
+};
+/** A sound's tail, whose highs the screen cannot tell. */
+const UNKNOWN_TINT = 0xb9c2ff;
+const PICKED = 0x5b45b8;
+const IDLE_ALPHA = 0.4;
+/** The ring a pixel of the tail is drawn with, and the strip of text under the screen. */
+const RING_STEP = 1.5;
+const TEXT_ROW = 14;
+
+function scopeStyle(size: number, fill: number): TextStyle {
+  const style = textStyle('small').clone();
+  style.fill = fill;
+  style.fontFamily = 'monospace';
+  style.fontSize = size;
+  style.fontWeight = 'bold';
+  return style;
+}
+
+function bezelStyle(): TextStyle {
+  const style = textStyle('small').clone();
+  style.fill = BEZEL_TEXT;
+  style.fontSize = 9;
+  style.fontWeight = 'bold';
+  style.letterSpacing = 1;
+  return style;
+}
+
+const tint = (bright: number | null): number =>
+  bright === null ? UNKNOWN_TINT : mixColor(SCOPE.dull, SCOPE.bright, bright);
+
+/** A type's button: its name on it, lit while it is the one. */
+class RoomButton extends Widget {
+  private readonly g = new Graphics();
+  private readonly caption: Text;
+  picked = false;
+
+  constructor(
+    readonly room: ReverbRoom,
+    name: string,
+    onPick: (room: ReverbRoom) => void,
+  ) {
+    super();
+    this.cursor = 'pointer';
+    this.caption = crispText({ text: name.toUpperCase(), style: scopeStyle(9, 0xe4e2ee) });
+    this.caption.anchor.set(0.5, 0.5);
+    this.caption.eventMode = 'none';
+    this.addChild(this.g, this.caption);
+    this.trackHover();
+    // A press on a button is not one on the node: it neither picks nor moves it.
+    this.on('pointerdown', (e: FederatedPointerEvent) => e.stopPropagation());
+    this.on('pointertap', (e: FederatedPointerEvent) => {
+      if (e.button === 0) onPick(room);
+    });
+  }
+
+  pick(on: boolean): void {
+    if (on === this.picked) return;
+    this.picked = on;
+    this.invalidate();
+  }
+
+  override redraw(): void {
+    const { w, h } = this;
+    const down = this.picked ? 1 : 0;
+    this.g
+      .clear()
+      .roundRect(0, 2, w, h - 2, 5)
+      .fill(0x24222f)
+      .roundRect(0, down, w, h - 2, 5)
+      .fill(this.picked ? PICKED : this.hovered ? 0x55536a : 0x45435a)
+      .stroke({ color: 0x1e1d27, width: 1 })
+      .roundRect(3, down + 2, w - 6, 4, 2)
+      .fill({ color: 0xffffff, alpha: this.picked ? 0.25 : 0.1 });
+    this.caption.position.set(Math.round(w / 2), Math.round(down + (h - 2) / 2));
+    this.caption.style.fill = this.picked ? 0xffffff : 0xd9d7e6;
+  }
+}
+
+/**
+ * The round screen: the sound as a dot in the middle, the tail as rings out from it on a scale of
+ * seconds, scattered reflections over it, and under it the pre-delay and the end.
+ */
+class ReverbScope extends Widget {
+  private readonly g = new Graphics();
+  private readonly marks: Text[];
+  private readonly under: Record<'pre' | 'ends', Text>;
+  tail: ReverbTail | null = null;
+  mix = 0;
+  /** What the texts under the screen say now, and the highs above it on the bezel (checks). */
+  says = { pre: '', highs: '', ends: '' };
+  /** How far out the tail reaches and the rings drawn (checks). */
+  reach = 0;
+  rings = 0;
+
+  constructor() {
+    super();
+    this.addChild(this.g);
+    this.marks = SCOPE_MARKS.map((seconds) => this.made(markText(seconds), 8, SCOPE.dim, 0, 1));
+    this.under = {
+      pre: this.made('', 9, SCOPE.text, 0, 0),
+      ends: this.made('', 9, SCOPE.text, 1, 0),
+    };
+  }
+
+  private made(text: string, size: number, fill: number, ax: number, ay: number): Text {
+    const t = crispText({ text, style: scopeStyle(size, fill) });
+    t.anchor.set(ax, ay);
+    t.eventMode = 'none';
+    this.addChild(t);
+    return t;
+  }
+
+  show(tail: ReverbTail | null, mix: number, missing: string): void {
+    this.tail = tail;
+    this.mix = mix;
+    this.says = scopeTexts(tail, missing);
+    this.invalidate();
+  }
+
+  /** The round part: a square above the strip of text. */
+  get disc(): { x: number; y: number; r: number } {
+    const side = Math.min(this.w, this.h - TEXT_ROW);
+    return { x: this.w / 2, y: side / 2, r: side / 2 - 10 };
+  }
+
+  override redraw(): void {
+    const { x: cx, y: cy, r: R } = this.disc;
+    const g = this.g.clear();
+    g.roundRect(0, 0, this.w, this.h - TEXT_ROW, 4).fill(SCOPE.glass);
+    for (const seconds of SCOPE_GRID) g.circle(cx, cy, scopeRadius(seconds) * R);
+    g.moveTo(cx - R, cy)
+      .lineTo(cx + R, cy)
+      .moveTo(cx, cy - R)
+      .lineTo(cx, cy + R);
+    g.stroke({ color: SCOPE.grid, width: 1 });
+
+    const tail = this.tail;
+    const shares = wetShares(this.mix);
+    this.reach = 0;
+    this.rings = 0;
+    if (tail) {
+      const rings = tailRings(tail, R, RING_STEP);
+      for (const ring of rings)
+        g.circle(cx, cy, ring.r).stroke({
+          color: tint(ring.bright),
+          width: RING_STEP,
+          alpha: ring.level * shares.tail,
+        });
+      for (const dot of reflections(tail, R))
+        g.circle(cx + Math.cos(dot.angle) * dot.r, cy + Math.sin(dot.angle) * dot.r, 1.2).fill({
+          color: tint(dot.bright),
+          alpha: Math.min(1, dot.level * shares.tail * 1.4),
+        });
+      // Where it has fallen by 60 dB: a dashed ring, as there is nothing left of it to see.
+      this.reach = scopeRadius(tail.predelay + tailSeconds(tail));
+      const end = this.reach * R;
+      const dashes = 48;
+      for (let i = 0; i < dashes; i += 2) {
+        const a = (i / dashes) * Math.PI * 2;
+        const b = ((i + 1) / dashes) * Math.PI * 2;
+        g.moveTo(cx + Math.cos(a) * end, cy + Math.sin(a) * end).lineTo(
+          cx + Math.cos(b) * end,
+          cy + Math.sin(b) * end,
+        );
+      }
+      g.stroke({ color: SCOPE.text, width: 1, alpha: 0.6 * Math.max(0.3, shares.tail) });
+      this.rings = rings.length;
+    }
+    g.circle(cx, cy, 3.5).fill({ color: 0xffffff, alpha: shares.dry });
+
+    // The scale up the middle, every other mark on the other side of the line, outer ones first:
+    // one that would still run into the last on its side is left out.
+    for (const side of [0, 1]) {
+      const order = [...this.marks.keys()].reverse().filter((_, k) => k % 2 === side);
+      const placed = order.map((i) => {
+        const t = this.marks[i]!;
+        t.anchor.set(side, 1);
+        t.position.set(
+          Math.round(cx + (side ? -3 : 3)),
+          Math.round(cy - scopeRadius(SCOPE_MARKS[i]!) * R - 1),
+        );
+        return { from: t.y - t.height, to: t.y };
+      });
+      const shown = apartLabels(placed, 1);
+      order.forEach((i, k) => (this.marks[i]!.visible = shown[k]!));
+    }
+
+    const y = this.h - TEXT_ROW + 3;
+    this.under.pre.text = this.says.pre;
+    this.under.pre.position.set(0, y);
+    this.under.ends.text = this.says.ends;
+    this.under.ends.position.set(this.w, y);
+  }
+}
+
+export class ReverbPanel extends Widget {
+  private readonly plate = new Graphics();
+  private readonly bezel = new Graphics();
+  private readonly rules = new Graphics();
+  readonly scope = new ReverbScope();
+  readonly roomButtons: RoomButton[];
+  readonly soundButton: Dropdown;
+  readonly knobs = {} as Record<ReverbKey, Knob>;
+  private readonly captions = {} as Record<ReverbKey, { ink: Text; edge: Text }>;
+  private readonly soundCaption: { ink: Text; edge: Text };
+  private readonly groupNames: { ink: Text; edge: Text }[];
+  private readonly title: { ink: Text; edge: Text };
+  private readonly screenName: Text;
+  /** Where the highs end up, above the screen on the right: there was no room for it below. */
+  readonly highs: Text;
+  /** The settings shown idle now (checks). */
+  idle: ReadonlySet<ReverbKey | 'impulse'> = new Set();
+
+  constructor(host: ReverbHost) {
+    super();
+    this.minWidth = REVERB_PANEL.w;
+    this.minHeight = REVERB_PANEL.h;
+    this.addChild(this.plate, this.rules, this.bezel, this.scope);
+    this.title = engrave(this, 'REVERB', 14);
+    this.screenName = crispText({ text: 'TAIL OVER TIME', style: bezelStyle() });
+    this.screenName.eventMode = 'none';
+    this.highs = crispText({ text: '', style: bezelStyle() });
+    this.highs.anchor.set(1, 0);
+    this.highs.eventMode = 'none';
+    this.addChild(this.screenName, this.highs);
+    this.groupNames = REVERB_LAYOUT.groups.map((group) => engrave(this, group.label, 9));
+    this.roomButtons = REVERB_ROOMS.map((room) => {
+      const button = new RoomButton(room.value, room.label, (picked) => host.pickRoom(picked));
+      this.addChild(button);
+      return button;
+    });
+    this.soundCaption = engrave(this, 'SOUND', 9);
+    this.soundButton = new Dropdown('No sound', {
+      width: REVERB_LAYOUT.sound.w,
+      onClick: () => host.pickSound(this.soundButton),
+    });
+    // A press on it is not one on the node.
+    this.soundButton.on('pointerdown', (e: FederatedPointerEvent) => e.stopPropagation());
+    this.addChild(this.soundButton);
+    for (const key of REVERB_KEYS) {
+      const row = REVERB_ROWS[key];
+      const look = REVERB_KNOBS[key];
+      const knob = new Knob('', row.default, {
+        min: row.min ?? 0,
+        max: row.max ?? 1,
+        step: row.step ?? 0.01,
+        taper: look.taper,
+        default: row.default,
+        decimals: look.decimals,
+        size: REVERB_LAYOUT.knobs[key].size,
+        look: 'chrome',
+        typed: false,
+        format: look.format,
+        ink: INK,
+        onInput: (value) => host.preview(key, value),
+        onChange: (value) => host.commit(key, value),
+      });
+      this.knobs[key] = knob;
+      this.captions[key] = engrave(this, look.label.toUpperCase(), 9);
+      this.addChild(knob);
+    }
+  }
+
+  override measure(): { w: number; h: number } {
+    return { ...REVERB_PANEL };
+  }
+
+  sync(shown: ReverbShown): void {
+    const v = shown.values;
+    for (const key of REVERB_KEYS) {
+      const knob = this.knobs[key];
+      knob.setValue(v[key]);
+      knob.setEnabled(!shown.wired(key));
+      knob.alpha = shown.idle.has(key) ? IDLE_ALPHA : 1;
+      this.captions[key].ink.alpha = knob.alpha;
+    }
+    for (const button of this.roomButtons) button.pick(button.room === v.room);
+    this.soundButton.setText(shown.sound || 'No sound');
+    this.soundButton.alpha = shown.idle.has('impulse') ? IDLE_ALPHA : 1;
+    this.soundCaption.ink.alpha = this.soundButton.alpha;
+    this.idle = shown.idle;
+    this.scope.show(shown.tail, v.mix, shown.missing);
+    this.highs.text = this.scope.says.highs;
+  }
+
+  override layout(): void {
+    const L = REVERB_LAYOUT;
+    const put = (widget: Widget, box: Box) => {
+      widget.position.set(Math.round(box.x), Math.round(box.y));
+      widget.resize(box.w, box.h);
+    };
+    put(this.scope, { ...L.screen, h: L.screen.h + TEXT_ROW });
+    this.screenName.position.set(L.screen.x, L.bezel.y + 3);
+    this.highs.position.set(L.screen.x + L.screen.w, L.bezel.y + 3);
+    this.roomButtons.forEach((button, i) => put(button, L.rooms[i]!));
+    const sound = this.soundButton.measure();
+    put(this.soundButton, { ...L.sound, y: L.sound.y + (L.sound.h - sound.h) / 2, h: sound.h });
+    placeEngraving(this.soundCaption, L.soundCaption.x, L.soundCaption.y);
+    for (const key of REVERB_KEYS) {
+      const spot = L.knobs[key];
+      const knob = this.knobs[key];
+      const size = knob.measure();
+      knob.position.set(Math.round(spot.x - size.w / 2), Math.round(spot.y - spot.size / 2));
+      knob.resize(size.w, size.h);
+      placeEngraving(this.captions[key], spot.x, spot.y - spot.size / 2 - KNOB_CAPTION);
+    }
+    L.groups.forEach((group, i) =>
+      placeEngraving(this.groupNames[i]!, group.box.x + group.box.w / 2, group.box.y),
+    );
+    placeEngraving(this.title, L.title.x + L.title.w / 2, L.title.y + 4);
+  }
+
+  override redraw(): void {
+    const L = REVERB_LAYOUT;
+    drawPlate(this.plate.clear(), REVERB_PANEL, LAVENDER, L.screws);
+    const b = L.bezel;
+    this.bezel
+      .clear()
+      .roundRect(b.x, b.y, b.w, b.h, 8)
+      .fill(BEZEL)
+      .roundRect(b.x + 0.5, b.y + 0.5, b.w - 1, b.h - 1, 8)
+      .stroke({ color: 0x1b1a24, width: 1 });
+    // A rule each side of a group's name, engraved as the names are.
+    const r = this.rules.clear();
+    L.groups.forEach((group, i) => {
+      const name = this.groupNames[i]!.ink;
+      const mid = group.box.y + 6;
+      const left = group.box.x + 6;
+      const right = group.box.x + group.box.w - 6;
+      const gap = name.width / 2 + 6;
+      const centre = group.box.x + group.box.w / 2;
+      if (centre - gap > left) r.moveTo(left, mid).lineTo(centre - gap, mid);
+      if (centre + gap < right) r.moveTo(centre + gap, mid).lineTo(right, mid);
+    });
+    r.stroke({ color: INK, width: 1, alpha: 0.5 });
+  }
+}

src/editor/soundfx/nodeFaces.ts

@@ -1,6 +1,12 @@
 import type { GraphNode } from '../../core/graph';
 import { InstrumentChip, InstrumentEnvelope } from '../../core/instrument/nodes';
-import { SoundFxCompressor, SoundFxFilter, SoundFxGain, SoundFxParametricEq } from '../../core/soundfx/nodes';
+import {
+  SoundFxCompressor,
+  SoundFxFilter,
+  SoundFxGain,
+  SoundFxParametricEq,
+  SoundFxReverb,
+} from '../../core/soundfx/nodes';
 import type { NodeFace } from '../graph/nodeFace';
 import type { EditorState } from '../state';
 import { ChipFace } from './ChipFace';
@@ -10,8 +16,9 @@ import { EnvelopeFace } from './EnvelopeFace';
 import { EqPanel } from './EqPanel';
 import { FilterPanel } from './FilterPanel';
 import { GainFace } from './GainFace';
+import { ReverbFace } from './ReverbFace';
 
-/** The nodes drawn as a face of their own instead of rows (#380, #381, #384–#386, #388), by type. */
+/** The nodes drawn as a face of their own instead of rows (#380, #381, #384–#386, #388, #389), by type. */
 export function nodeFaceFor(state: EditorState, assetId: string, node: GraphNode): NodeFace | null {
   if (node.type === InstrumentChip.type) return new ChipFace(state, assetId, node.id);
   if (node.type === InstrumentEnvelope.type) return new EnvelopeFace(state, assetId, node.id);
@@ -20,5 +27,6 @@ export function nodeFaceFor(state: EditorState, assetId: string, node: GraphNode
     return new CurveFace(new EqPanel(state, true), assetId, node.id);
   if (node.type === SoundFxFilter.type) return new CurveFace(new FilterPanel(state, true), assetId, node.id);
   if (node.type === SoundFxGain.type) return new GainFace(state, assetId, node.id);
+  if (node.type === SoundFxReverb.type) return new ReverbFace(state, assetId, node.id);
   return null;
 }

src/editor/soundfx/nodeParamDrag.ts

@@ -1,3 +1,4 @@
+import { oneStep } from '../../core/commands/CompoundCommand';
 import { SetNodeParamCommand } from '../../core/commands/graphCommands';
 import type { GraphNode } from '../../core/graph';
 import type { PropertyValue } from '../../core/model/Properties';
@@ -6,11 +7,12 @@ import type { EditorState } from '../state';
 
 /**
  * A number of a node turned by a knob: written into the node as it goes, one undo step when it
- * ends. A Compressor's tab (#378) and its node (#380) each have one.
+ * ends. A Compressor's tab (#378) and its node (#380) each have one. A drag may write several
+ * settings at once (#389), a Reverb's knob that takes it from a room to Custom.
  */
 export class NodeParamDrag {
-  /** The value a drag began with – its undo step's other side; undefined when none was typed in. */
-  private before: { key: string; value: PropertyValue | undefined } | null = null;
+  /** The values a drag began with – its undo step's other side; undefined where none was typed in. */
+  private readonly before = new Map<string, PropertyValue | undefined>();
   private readonly perFrame: FramePreview;
 
   constructor(
@@ -21,37 +23,63 @@ export class NodeParamDrag {
   }
 
   preview(node: GraphNode, key: string, value: number): void {
-    if (this.before?.key !== key) {
-      this.restore(node);
-      this.before = { key, value: node.params[key] };
+    this.previewAll(node, { [key]: value });
+  }
+
+  /** Writes several settings as one drag; one other than the last drag wrote begins a new one. */
+  previewAll(node: GraphNode, values: Record<string, PropertyValue>): void {
+    if ([...this.before.keys()].some((key) => !(key in values))) this.restore(node);
+    for (const [key, value] of Object.entries(values)) {
+      if (!this.before.has(key)) this.before.set(key, node.params[key]);
+      node.params[key] = value;
     }
-    node.params[key] = value;
     this.perFrame.request();
   }
 
+  /** Whether the drag going on has written this setting. */
+  holds(key: string): boolean {
+    return this.before.has(key);
+  }
+
   commit(assetId: string, node: GraphNode, key: string, value: PropertyValue): void {
+    this.commitAll(assetId, node, { [key]: value }, `Set ${key}`);
+  }
+
+  /** What the drag going on wrote, as one undo step. */
+  commitHeld(assetId: string, node: GraphNode, label: string): void {
+    const values: Record<string, PropertyValue> = {};
+    for (const key of this.before.keys()) if (node.params[key] !== undefined) values[key] = node.params[key];
+    this.commitAll(assetId, node, values, label);
+  }
+
+  private commitAll(
+    assetId: string,
+    node: GraphNode,
+    values: Record<string, PropertyValue>,
+    label: string,
+  ): void {
     this.perFrame.cancel();
     this.restore(node);
-    if (node.params[key] === value) {
-      this.state.preview();
-      return;
-    }
-    this.state.execute(new SetNodeParamCommand(assetId, node.id, key, value));
+    const commands = Object.entries(values)
+      .filter(([key, value]) => node.params[key] !== value)
+      .map(([key, value]) => new SetNodeParamCommand(assetId, node.id, key, value));
+    if (commands.length === 0) this.state.preview();
+    else this.state.execute(commands.length === 1 ? commands[0]! : oneStep(label, commands));
   }
 
   /** The node as it was before the drag, which is left without a step. */
   restore(node: GraphNode): void {
-    const before = this.before;
-    if (!before) return;
-    if (before.value === undefined) delete node.params[before.key];
-    else node.params[before.key] = before.value;
-    this.before = null;
+    for (const [key, value] of this.before) {
+      if (value === undefined) delete node.params[key];
+      else node.params[key] = value;
+    }
+    this.before.clear();
   }
 
   /** Another node: what was begun on the last one is dropped. */
   forget(): void {
     this.perFrame.cancel();
-    this.before = null;
+    this.before.clear();
   }
 
   cancel(): void {

src/editor/soundfx/reverbView.ts

@@ -0,0 +1,322 @@
+/**
+ * What a Reverb's node draws (#389), as numbers: where the parts of its device sit, how its knobs
+ * turn, which numbers its type takes, and its tail as rings out from the sound – the round screen.
+ * Kept apart from the drawing so it is checked without a browser.
+ */
+import type { PropertyBag } from '../../core/model/Properties';
+import { REVERB_IMPULSE_KEY, REVERB_ROWS, reverbRoomOf } from '../../core/soundfx/nodes';
+import {
+  DAMPED_HZ,
+  OPEN_HZ,
+  REVERB_MAX_DECAY,
+  REVERB_PRESETS,
+  REVERB_ROOMS,
+  type ReverbRoom,
+  reverbCutoff,
+  seededNoise,
+} from '../../core/soundfx/reverb';
+import { formatNumber } from '../../ui/math';
+import { secondsText } from './chipView';
+import { type Box, type KnobSpot, KNOB_CAPTION, screwsOf, SMALL_DIAL } from './hardwareView';
+
+export type ReverbKey = keyof typeof REVERB_ROWS;
+export const REVERB_KEYS = Object.keys(REVERB_ROWS) as ReverbKey[];
+/** The numbers a room sets itself, and a sound brings but the pre-delay. */
+const SHAPE_KEYS: readonly ReverbKey[] = ['decay', 'damping', 'predelay'];
+
+export interface ReverbValues extends Record<ReverbKey, number> {
+  room: ReverbRoom;
+  /** The sound asset that is the impulse response, '' for none. */
+  impulse: string;
+}
+
+const numberOf = (params: PropertyBag, key: ReverbKey): number => {
+  const value = params[key];
+  return typeof value === 'number' && Number.isFinite(value) ? value : REVERB_ROWS[key].default;
+};
+
+/**
+ * The numbers a Reverb plays with, as its knobs show them: a room's own decay, damping and
+ * pre-delay, else the node's, each its row's default where none is typed in.
+ */
+export function reverbValues(params: PropertyBag): ReverbValues {
+  const room = reverbRoomOf(params);
+  const preset = room === 'custom' || room === 'sound' ? null : REVERB_PRESETS[room];
+  const impulse = params[REVERB_IMPULSE_KEY];
+  return {
+    room,
+    impulse: typeof impulse === 'string' ? impulse : '',
+    decay: preset?.decay ?? numberOf(params, 'decay'),
+    damping: preset?.damping ?? numberOf(params, 'damping'),
+    predelay: preset?.predelay ?? numberOf(params, 'predelay'),
+    mix: numberOf(params, 'mix'),
+  };
+}
+
+/** Whether a type plays a number as it is set: a room has its own, a sound its own decay and damping. */
+export function roomTakes(room: ReverbRoom, key: ReverbKey): boolean {
+  if (key === 'mix' || room === 'custom') return true;
+  return room === 'sound' && key === 'predelay';
+}
+
+/**
+ * The settings that do nothing as things stand, greyed as the Chip's are – still to be turned: a
+ * knob the type does not take goes over to Custom with it. The sound while the type is not Sound.
+ */
+export function idleReverbKeys(room: ReverbRoom): Set<ReverbKey | 'impulse'> {
+  const idle = new Set<ReverbKey | 'impulse'>(SHAPE_KEYS.filter((key) => !roomTakes(room, key)));
+  if (room !== 'sound') idle.add('impulse');
+  return idle;
+}
+
+/**
+ * What a knob of a type that does not take it writes (#389): Custom, with the numbers the knobs
+ * showed, so the sound changes by that one knob only.
+ */
+export function customFrom(
+  values: ReverbValues,
+  key: ReverbKey,
+  value: number,
+): Record<string, number | string> {
+  return {
+    room: 'custom',
+    decay: values.decay,
+    damping: values.damping,
+    predelay: values.predelay,
+    [key]: value,
+  };
+}
+
+export interface ReverbKnob {
+  label: string;
+  taper: number;
+  decimals: number;
+  format: (value: number) => string;
+}
+
+export const percentText = (share: number): string => `${formatNumber(Math.round(share * 100), 0)}%`;
+
+/**
+ * How each knob turns: the decay gives its first seconds most of the turn – a room's 0.6 s sits at
+ * a third, a hall's 2.5 s past the middle – the pre-delay its first tens of milliseconds.
+ */
+export const REVERB_KNOBS: Record<ReverbKey, ReverbKnob> = {
+  decay: { label: 'Decay', taper: 3, decimals: 2, format: secondsText },
+  damping: { label: 'Damping', taper: 1, decimals: 2, format: percentText },
+  predelay: { label: 'Pre-delay', taper: 2, decimals: 3, format: secondsText },
+  mix: { label: 'Wet', taper: 1, decimals: 2, format: percentText },
+};
+
+// --- The plate. ---
+
+/** The plate: as the Compressor's (#379), the panel never takes another size. */
+export const REVERB_PANEL = { w: 640, h: 280 };
+
+/** The round screen's side, and the radius of its outer ring inside it. */
+export const SCOPE_SIZE = 176;
+const KNOB_SLOT = 64;
+const GROUP_GAP = 22;
+/** The height of a group's name and its rule. */
+const GROUP_LINE = 16;
+const ROOM_BUTTON = { w: 54, h: 30, gap: 6 };
+const SOUND_ROW = 24;
+const SOUND_CAPTION = 52;
+
+export interface ReverbLayout {
+  title: Box;
+  /** The dark frame round the screen, and the screen in it. */
+  bezel: Box;
+  screen: Box;
+  groups: { label: string; box: Box }[];
+  rooms: Box[];
+  /** The picked sound, its name engraved before it. */
+  sound: Box;
+  soundCaption: { x: number; y: number };
+  knobs: Record<ReverbKey, KnobSpot>;
+  screws: { x: number; y: number }[];
+}
+
+function reverbLayout(): ReverbLayout {
+  const { w } = REVERB_PANEL;
+  const bezel = { x: 24, y: 44, w: SCOPE_SIZE + 20, h: SCOPE_SIZE + 36 };
+  const screen = { x: bezel.x + 10, y: bezel.y + 16, w: SCOPE_SIZE, h: SCOPE_SIZE };
+  // The right of the plate: the types on top, the sound under them, the knobs below.
+  const left = bezel.x + bezel.w + 24;
+  const right = w - 24;
+  const roomsWidth = REVERB_ROOMS.length * (ROOM_BUTTON.w + ROOM_BUTTON.gap) - ROOM_BUTTON.gap;
+  const roomsX = left + (right - left - roomsWidth) / 2;
+  const groups: { label: string; box: Box }[] = [
+    { label: 'TYPE', box: { x: roomsX, y: bezel.y, w: roomsWidth, h: GROUP_LINE } },
+  ];
+  const rooms = REVERB_ROOMS.map((_, i) => ({
+    x: roomsX + i * (ROOM_BUTTON.w + ROOM_BUTTON.gap),
+    y: bezel.y + GROUP_LINE + 2,
+    w: ROOM_BUTTON.w,
+    h: ROOM_BUTTON.h,
+  }));
+  const soundY = rooms[0]!.y + ROOM_BUTTON.h + 10;
+  const sound = { x: roomsX + SOUND_CAPTION, y: soundY, w: roomsWidth - SOUND_CAPTION, h: SOUND_ROW };
+  const space = SHAPE_KEYS.length * KNOB_SLOT;
+  const groupTop = soundY + SOUND_ROW + 14;
+  const dialY = groupTop + GROUP_LINE + KNOB_CAPTION + SMALL_DIAL / 2;
+  let x = left + (right - left - space - GROUP_GAP - KNOB_SLOT) / 2;
+  groups.push({ label: 'SPACE', box: { x, y: groupTop, w: space, h: GROUP_LINE } });
+  const knobs = {} as Record<ReverbKey, KnobSpot>;
+  for (const key of SHAPE_KEYS) {
+    knobs[key] = { x: x + KNOB_SLOT / 2, y: dialY, size: SMALL_DIAL };
+    x += KNOB_SLOT;
+  }
+  x += GROUP_GAP;
+  groups.push({ label: 'MIX', box: { x, y: groupTop, w: KNOB_SLOT, h: GROUP_LINE } });
+  knobs.mix = { x: x + KNOB_SLOT / 2, y: dialY, size: SMALL_DIAL };
+  return {
+    title: { x: 34, y: 14, w: 120, h: 24 },
+    bezel,
+    screen,
+    groups,
+    rooms,
+    sound,
+    soundCaption: { x: roomsX + SOUND_CAPTION / 2 - 4, y: soundY + (SOUND_ROW - KNOB_CAPTION) / 2 + 2 },
+    knobs,
+    screws: screwsOf(REVERB_PANEL),
+  };
+}
+
+export const REVERB_LAYOUT: ReverbLayout = reverbLayout();
+
+// --- The screen: the tail as rings out from the sound. ---
+
+/** The time at the outer ring: the longest decay after the longest pre-delay. */
+export const SCOPE_SECONDS = REVERB_MAX_DECAY + REVERB_ROWS.predelay.max!;
+/** The rings drawn faintly as a scale, in seconds; the ones with a number. */
+export const SCOPE_GRID = [0.1, 0.5, 1, 2, 5, 10];
+export const SCOPE_MARKS = [1, 2, 5, 10];
+
+/**
+ * How far out a time sits, 0 at the sound to 1 at the outer ring: as the root of its seconds, so a
+ * room's tail of 0.6 s is a small disc and a cave's of 5 s fills two thirds – every Reverb on the
+ * same scale, so their sizes compare.
+ */
+export function scopeRadius(seconds: number): number {
+  return Math.sqrt(Math.min(SCOPE_SECONDS, Math.max(0, seconds)) / SCOPE_SECONDS);
+}
+
+export function scopeSeconds(radius: number): number {
+  return Math.max(0, Math.min(1, radius)) ** 2 * SCOPE_SECONDS;
+}
+
+/** The tail a Reverb rings: made from its decay and damping, or a sound's, known by its peaks. */
+export type ReverbTail =
+  | { kind: 'made'; predelay: number; decay: number; damping: number }
+  | { kind: 'sound'; predelay: number; seconds: number; peaks: Float32Array };
+
+/** A point of the tail: how loud it still is, 1 at its start to 0 at 60 dB down, and how bright. */
+export interface TailPoint {
+  level: number;
+  /** How much of the highs is left, 1 all of them to 0 down to 500 Hz; null where a sound tells nothing of it. */
+  bright: number | null;
+}
+
+/** How long a tail rings after its pre-delay. */
+export function tailSeconds(tail: ReverbTail): number {
+  return tail.kind === 'made' ? Math.min(REVERB_MAX_DECAY, Math.max(0.01, tail.decay)) : tail.seconds;
+}
+
+/** The cut-off of the highs as a share of the way from 500 Hz up to 20 kHz, in octaves. */
+export function brightness(hz: number): number {
+  return Math.max(0, Math.min(1, Math.log2(hz / DAMPED_HZ) / Math.log2(OPEN_HZ / DAMPED_HZ)));
+}
+
+/**
+ * The tail `seconds` after the sound, or null outside it: a made one falls by 60 dB in its decay,
+ * evenly in dB as the screen draws it, its highs closing as the impulse response's do. A sound's is
+ * as loud as its loudest peak there against its loudest of all.
+ */
+export function tailAt(tail: ReverbTail, seconds: number): TailPoint | null {
+  const length = tailSeconds(tail);
+  const into = seconds - tail.predelay;
+  if (into < 0 || into > length || length <= 0) return null;
+  const share = into / length;
+  if (tail.kind === 'made')
+    return { level: 1 - share, bright: brightness(reverbCutoff(tail.damping, share)) };
+  const peaks = tail.peaks;
+  let loudest = 0;
+  for (const p of peaks) loudest = Math.max(loudest, p);
+  if (loudest <= 0 || peaks.length === 0) return { level: 0, bright: null };
+  const peak = peaks[Math.min(peaks.length - 1, Math.floor(share * peaks.length))]!;
+  const db = peak > 0 ? 20 * Math.log10(peak / loudest) : -Infinity;
+  return { level: Math.max(0, 1 + db / 60), bright: null };
+}
+
+export interface TailRing extends TailPoint {
+  /** Its radius in pixels. */
+  r: number;
+}
+
+/**
+ * The tail as rings `step` pixels wide out to `radius`, each as loud and bright as the tail is at
+ * its time; none where the tail is silent.
+ */
+export function tailRings(tail: ReverbTail, radius: number, step = 1.5): TailRing[] {
+  const rings: TailRing[] = [];
+  for (let r = step / 2; r < radius; r += step) {
+    const point = tailAt(tail, scopeSeconds(r / radius));
+    if (point && point.level > 0) rings.push({ r, ...point });
+  }
+  return rings;
+}
+
+export interface Reflection extends TailPoint {
+  r: number;
+  angle: number;
+}
+
+/** Reflections scattered over the tail, as many as a dense tail has – the same ones each time. */
+const REFLECTIONS = 90;
+
+/**
+ * Dots over the tail, at angles of their own and more of them the further it has gone, as the
+ * echoes of a room grow thicker; each as loud and bright as the tail where it sits.
+ */
+export function reflections(tail: ReverbTail, radius: number): Reflection[] {
+  const next = seededNoise(389);
+  const length = tailSeconds(tail);
+  const dots: Reflection[] = [];
+  for (let i = 0; i < REFLECTIONS; i++) {
+    const along = Math.sqrt((next() + 1) / 2);
+    const angle = next() * Math.PI;
+    const point = tailAt(tail, tail.predelay + along * length);
+    if (point && point.level > 0)
+      dots.push({ r: scopeRadius(tail.predelay + along * length) * radius, angle, ...point });
+  }
+  return dots;
+}
+
+/** How strongly the tail is drawn, and the sound at its middle: the wet against the dry. */
+export function wetShares(mix: number): { tail: number; dry: number } {
+  const wet = Math.max(0, Math.min(1, mix));
+  return { tail: Math.sqrt(wet), dry: Math.max(0.2, Math.sqrt(1 - wet)) };
+}
+
+/** A frequency as the screen writes it: `500 Hz`, `4.1 kHz`. */
+export function hzText(hz: number): string {
+  return hz >= 1000 ? `${formatNumber(hz / 1000, 1)} kHz` : `${formatNumber(Math.round(hz), 0)} Hz`;
+}
+
+/** What the screen writes under it: the pre-delay, where the highs end up, when the tail has died. */
+export function scopeTexts(
+  tail: ReverbTail | null,
+  missing: string,
+): { pre: string; highs: string; ends: string } {
+  if (!tail) return { pre: '', highs: '', ends: missing };
+  return {
+    pre: `PRE ${secondsText(tail.predelay)}`,
+    highs: tail.kind === 'made' ? `HIGHS ${hzText(reverbCutoff(tail.damping, 1))}` : '',
+    ends: `ENDS ${secondsText(tail.predelay + tailSeconds(tail))}`,
+  };
+}
+
+/** A mark of the scale as it is written beside its ring. */
+export function markText(seconds: number): string {
+  return seconds >= 1 ? `${formatNumber(seconds, 0)}s` : formatNumber(seconds, 1);
+}