Show a Gain node as an orange device with one knob (#384)

A Gain node now draws a small device in the graph, as the Compressor
does since #380: the brushed plate in orange, 160x220 graph units, with
one chrome knob between its inputs and its output.

- GainPanel and GainFace join the node faces. The knob drags, resets
  on a double-click and keeps the wheel for the graph (#383). Each turn
  is one undo step, a linked Gain (dB) greys it.
- The knob turns with a taper of 0.26, so 0 dB stands straight up and
  the range below -24 dB takes a fifth of the turn.
- drawPlate, engrave and the brushed look move out of CompressorPanel
  so both devices share them. The Knob takes an arc colour, because
  the orange arc vanished on the orange plate.
- No meter and no tap. Gain sits in every voice of an instrument, and
  a tap would add two audio nodes to each note for a display nobody
  asked for.

Found on the way:
- Knob.dialGlobal added half the dial unscaled. In a zoomed graph it
  pointed beside the dial. The Compressor's e2e only hit by luck.

Tests:
- Unit: 2 new for the Gain plate and its taper.
- e2e 34 on atx: ALL PASSED, 126 checks (1 new).
- Gate on atx: CHECK EXIT 0, 283 files, 4359 tests.

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

README.md

@@ -47,7 +47,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1956 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1957 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs

src/core/soundfx/nodes.ts

@@ -535,7 +535,7 @@ export const SoundFxOutput: SoundFxNodeDef = {
   emit: arriving,
 };
 
-const GAIN = numberRow('gain', 'Gain (dB)', -120, 24, 0.5);
+export const GAIN_ROW = numberRow('gain', 'Gain (dB)', -120, 24, 0.5);
 
 /** How an effect with a Bypass and a Wet says so, at the end of its description (#354). */
 const BLENDS =
@@ -549,11 +549,11 @@ export const SoundFxGain: SoundFxNodeDef = effect(
     description:
       'Makes the sound louder or quieter, in decibels: 0 leaves it as it is, -6 is about half as loud, +6 twice. Above 0 it can clip.' +
       BLENDS,
-    inputs: [audioIn, followingIn(GAIN)],
+    inputs: [audioIn, followingIn(GAIN_ROW)],
     outputs: [audioOut],
     params: [],
     emit: (sounds, amounts) => {
-      const db = held(amounts.gain, GAIN);
+      const db = held(amounts.gain, GAIN_ROW);
       return withStages(arriving(sounds), isNone(db) ? [] : [{ kind: 'gain', db }]);
     },
   },

src/editor/debug/graphHooks.ts

@@ -4,6 +4,7 @@ import { soundLibrary } from '../../viewport/SoundLibrary';
 import type { Widget } from '../../ui';
 import { currentNodePalette } from '../graph/NodePalette';
 import { CompressorPanel } from '../soundfx/CompressorPanel';
+import { GainPanel } from '../soundfx/GainPanel';
 import { EqPanel } from '../soundfx/EqPanel';
 import { rectOf } from '../textProbe';
 import { centreOf, snapButton, type HookContext } from './hookHelpers';
@@ -243,6 +244,34 @@ export function graphHooks({ state, editor }: HookContext) {
         };
       },
     },
+    /**
+     * The panel a Gain node shows in the sound FX graph (#384): whether it is shown and where, its
+     * knob, and the node's ports.
+     */
+    gain: {
+      panel: (nodeId: string) => {
+        const canvas = editor.soundFxEditor.canvas;
+        const panel = canvas.faceOf(nodeId)?.widget;
+        if (!(panel instanceof GainPanel)) 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),
+          knob: {
+            value: panel.knob.value,
+            enabled: panel.knob.enabled,
+            number: panel.knob.shown,
+            dial: panel.knob.dialGlobal(),
+          },
+        };
+      },
+    },
     instrument: {
       current: () => editor.instrumentEditor.currentAssetId,
       info: () => editor.instrumentEditor.shownInfo,

src/editor/soundfx/CompressorEditor.ts

@@ -501,8 +501,8 @@ export class CompressorEditor extends VStack implements CompressorHost {
   }
 }
 
-/** Whether a link decides one of a Compressor's numbers: its knob is greyed then. */
-export function compressorWired(project: Project, assetId: string, nodeId: string, key: Key): boolean {
+/** Whether a link decides one of a Compressor's (or a Gain's, #384) numbers: its knob is greyed then. */
+export function compressorWired(project: Project, assetId: string, nodeId: string, key: string): boolean {
   const graph = findGraphAsset(project, assetId)?.graph;
   return Boolean(graph?.edges.some((e) => e.to.node === nodeId && e.to.port === key));
 }

src/editor/soundfx/CompressorPanel.ts

@@ -46,12 +46,12 @@ export interface PanelHost {
   switchAutoGain(on: boolean): void;
 }
 
-const INK = 0x26282c;
+export const INK = 0x26282c;
 const LCD_GLOW = 0x9cf58c;
 const LED_LIT = { green: 0x4dff5a, amber: 0xffc21a, red: 0xff3b2a };
 
 /** Captions are engraved: dark letters with a light edge under them. */
-function engrave(parent: Container, text: string, size = 10): { ink: Text; edge: Text } {
+export function engrave(parent: Container, text: string, size = 10): { ink: Text; edge: Text } {
   const style = (fill: number): TextStyle => {
     const s = textStyle('small').clone();
     s.fill = fill;
@@ -71,12 +71,11 @@ function engrave(parent: Container, text: string, size = 10): { ink: Text; edge:
   return { ink, edge };
 }
 
-function placeEngraving(e: { ink: Text; edge: Text }, x: number, y: number): void {
+export function placeEngraving(e: { ink: Text; edge: Text }, x: number, y: number): void {
   e.ink.position.set(Math.round(x), Math.round(y));
   e.edge.position.set(Math.round(x), Math.round(y) + 1);
 }
 
-let plateFill: FillGradient | null = null;
 let faceFill: FillGradient | null = null;
 const gradient = (stops: [number, number][], end = { x: 0, y: 1 }) =>
   new FillGradient({
@@ -87,6 +86,55 @@ const gradient = (stops: [number, number][], end = { x: 0, y: 1 }) =>
     textureSpace: 'local',
   });
 
+/** The metal of a plate: its shade from top to bottom, its rim, and the dark strokes of the brush. */
+export interface PlateLook {
+  stops: [number, number][];
+  rim: number;
+  grain: number;
+}
+
+/** Brushed aluminium, the Compressor's. */
+const ALUMINIUM: PlateLook = {
+  stops: [
+    [0, 0xe2e4e7],
+    [0.5, 0xcfd2d6],
+    [1, 0xb4b8bd],
+  ],
+  rim: 0x8a8e94,
+  grain: 0x6c7076,
+};
+
+const plateFills = new WeakMap<PlateLook, FillGradient>();
+
+/** A brushed plate with a screw in each corner. */
+export function drawPlate(
+  g: Graphics,
+  size: { w: number; h: number },
+  look: PlateLook,
+  screws: readonly { x: number; y: number }[],
+): void {
+  const { w, h } = size;
+  let fill = plateFills.get(look);
+  if (!fill) plateFills.set(look, (fill = gradient(look.stops)));
+  g.roundRect(0, 0, w, h, 6).fill(fill);
+  for (const stroke of brushStrokes(h - 4))
+    g.rect(3, stroke.y + 2, w - 6, 1).fill({
+      color: stroke.light ? 0xffffff : look.grain,
+      alpha: stroke.alpha,
+    });
+  g.roundRect(0.5, 0.5, w - 1, h - 1, 6).stroke({ color: look.rim, width: 1 });
+  g.moveTo(3, 1.5)
+    .lineTo(w - 3, 1.5)
+    .stroke({ color: 0xffffff, width: 1, alpha: 0.8 });
+  for (const screw of screws) {
+    g.circle(screw.x, screw.y, 6).fill(0x9a9ea4).stroke({ color: 0x5f6369, width: 1 });
+    g.circle(screw.x - 1, screw.y - 1, 4).fill({ color: 0xffffff, alpha: 0.35 });
+    g.moveTo(screw.x - 4, screw.y + 3)
+      .lineTo(screw.x + 4, screw.y - 3)
+      .stroke({ color: 0x45484d, width: 1.5 });
+  }
+}
+
 /** The meter: a lit face, a scale from 0 to the range, and a needle that swings as a VU's does. */
 class ReductionMeter extends Widget {
   private readonly face = new Graphics();
@@ -201,7 +249,7 @@ class ReductionMeter extends Widget {
 }
 
 /** The level going out, as a column of LEDs: lit at once, going out slowly. */
-class OutputLeds extends Widget {
+export class OutputLeds extends Widget {
   private readonly lights = new Graphics();
   shown = -Infinity;
   private lit = -1;
@@ -430,30 +478,7 @@ export class CompressorPanel extends Widget {
   }
 
   override redraw(): void {
-    const { w, h } = PANEL;
-    const g = this.plate.clear();
-    plateFill ??= gradient([
-      [0, 0xe2e4e7],
-      [0.5, 0xcfd2d6],
-      [1, 0xb4b8bd],
-    ]);
-    g.roundRect(0, 0, w, h, 6).fill(plateFill);
-    for (const stroke of brushStrokes(h - 4))
-      g.rect(3, stroke.y + 2, w - 6, 1).fill({
-        color: stroke.light ? 0xffffff : 0x6c7076,
-        alpha: stroke.alpha,
-      });
-    g.roundRect(0.5, 0.5, w - 1, h - 1, 6).stroke({ color: 0x8a8e94, width: 1 });
-    g.moveTo(3, 1.5)
-      .lineTo(w - 3, 1.5)
-      .stroke({ color: 0xffffff, width: 1, alpha: 0.8 });
-    for (const screw of PANEL_LAYOUT.screws) {
-      g.circle(screw.x, screw.y, 6).fill(0x9a9ea4).stroke({ color: 0x5f6369, width: 1 });
-      g.circle(screw.x - 1, screw.y - 1, 4).fill({ color: 0xffffff, alpha: 0.35 });
-      g.moveTo(screw.x - 4, screw.y + 3)
-        .lineTo(screw.x + 4, screw.y - 3)
-        .stroke({ color: 0x45484d, width: 1.5 });
-    }
+    drawPlate(this.plate.clear(), PANEL, ALUMINIUM, PANEL_LAYOUT.screws);
     const lcd = PANEL_LAYOUT.lcd;
     this.lcdBox
       .clear()

src/editor/soundfx/GainFace.ts

@@ -0,0 +1,59 @@
+import type { GraphNode } from '../../core/graph';
+import { findGraphAsset } from '../../core/model/Project';
+import { GAIN_ROW, SoundFxGain } from '../../core/soundfx/nodes';
+import type { NodeFace } from '../graph/nodeFace';
+import type { EditorState } from '../state';
+import { compressorWired } from './CompressorEditor';
+import { type GainHost, GainPanel } from './GainPanel';
+import { NodeParamDrag } from './nodeParamDrag';
+
+/**
+ * A Gain node drawn as its device (#384): one knob, turned right in the graph. It listens to
+ * nothing, so it has nothing to move between changes.
+ */
+export class GainFace implements NodeFace, GainHost {
+  readonly widget: GainPanel;
+  private readonly drag: NodeParamDrag;
+
+  constructor(
+    private readonly state: EditorState,
+    private readonly assetId: string,
+    private readonly nodeId: string,
+  ) {
+    this.widget = new GainPanel(this);
+    this.drag = new NodeParamDrag(state, 'gain-face');
+  }
+
+  private node(): GraphNode | null {
+    const node = findGraphAsset(this.state.project, this.assetId)?.graph.nodes.find(
+      (n) => n.id === this.nodeId,
+    );
+    return node?.type === SoundFxGain.type ? node : null;
+  }
+
+  sync(): void {
+    const node = this.node();
+    if (!node) return;
+    const db = node.params[GAIN_ROW.key];
+    this.widget.sync(
+      typeof db === 'number' && Number.isFinite(db) ? db : GAIN_ROW.default,
+      compressorWired(this.state.project, this.assetId, this.nodeId, GAIN_ROW.key),
+    );
+  }
+
+  tick(): boolean {
+    return false;
+  }
+
+  hide(): void {}
+
+  preview(value: number): void {
+    const node = this.node();
+    if (node) this.drag.preview(node, GAIN_ROW.key, value);
+  }
+
+  commit(value: number): void {
+    const node = this.node();
+    if (node) this.drag.commit(this.assetId, node, GAIN_ROW.key, value);
+  }
+}

src/editor/soundfx/GainPanel.ts

@@ -0,0 +1,85 @@
+/**
+ * The Gain as a device (#384), what its node shows in the graph: the Compressor's plate (#379) in
+ * orange, with one big chrome knob.
+ */
+import { Graphics, type Text } from 'pixi.js';
+import { Knob, Widget } from '../../ui';
+import { GAIN_ROW } from '../../core/soundfx/nodes';
+import { drawPlate, engrave, INK, placeEngraving, type PlateLook } from './CompressorPanel';
+import { GAIN_LAYOUT, GAIN_PANEL, GAIN_TAPER, KNOB_CAPTION } from './hardwareView';
+
+/** What the panel asks of the node it sits in. */
+export interface GainHost {
+  preview(value: number): void;
+  commit(value: number): void;
+}
+
+/** Brushed anodised orange. */
+const ORANGE: PlateLook = {
+  stops: [
+    [0, 0xffb25e],
+    [0.5, 0xf39433],
+    [1, 0xd8761c],
+  ],
+  rim: 0xa85616,
+  grain: 0x8a3e08,
+};
+/** The knob's value arc: the usual orange would vanish on this plate. */
+const DARK_ARC = 0x3b1a06;
+
+export class GainPanel extends Widget {
+  private readonly plate = new Graphics();
+  readonly knob: Knob;
+  private readonly title: { ink: Text; edge: Text };
+  private readonly caption: { ink: Text; edge: Text };
+
+  constructor(host: GainHost) {
+    super();
+    this.minWidth = GAIN_PANEL.w;
+    this.minHeight = GAIN_PANEL.h;
+    this.addChild(this.plate);
+    this.title = engrave(this, 'GAIN', 14);
+    this.caption = engrave(this, 'DB', 11);
+    const row = GAIN_ROW;
+    this.knob = new Knob('', row.default, {
+      min: row.min ?? 0,
+      max: row.max ?? 0,
+      step: row.step ?? 1,
+      taper: GAIN_TAPER,
+      default: row.default,
+      decimals: 1,
+      size: GAIN_LAYOUT.knob.size,
+      look: 'chrome',
+      typed: false,
+      ink: INK,
+      arc: DARK_ARC,
+      onInput: (value) => host.preview(value),
+      onChange: (value) => host.commit(value),
+    });
+    this.addChild(this.knob);
+  }
+
+  override measure(): { w: number; h: number } {
+    return { ...GAIN_PANEL };
+  }
+
+  /** The node's gain, and whether a link feeds it, which greys the knob. */
+  sync(db: number, wired: boolean): void {
+    this.knob.setValue(db);
+    this.knob.setEnabled(!wired);
+  }
+
+  override layout(): void {
+    const L = GAIN_LAYOUT;
+    const spot = L.knob;
+    const size = this.knob.measure();
+    this.knob.position.set(Math.round(spot.x - size.w / 2), Math.round(spot.y - spot.size / 2));
+    this.knob.resize(size.w, size.h);
+    placeEngraving(this.caption, spot.x, spot.y - spot.size / 2 - KNOB_CAPTION);
+    placeEngraving(this.title, L.title.x, L.title.y + 6);
+  }
+
+  override redraw(): void {
+    drawPlate(this.plate.clear(), GAIN_PANEL, ORANGE, GAIN_LAYOUT.screws);
+  }
+}

src/editor/soundfx/hardwareView.ts

@@ -46,6 +46,16 @@ export interface PanelLayout {
 
 const SCREW_INSET = 14;
 
+/** A screw in each corner of a plate. */
+export function screwsOf(plate: { w: number; h: number }): { x: number; y: number }[] {
+  return [
+    { x: SCREW_INSET, y: SCREW_INSET },
+    { x: plate.w - SCREW_INSET, y: SCREW_INSET },
+    { x: SCREW_INSET, y: plate.h - SCREW_INSET },
+    { x: plate.w - SCREW_INSET, y: plate.h - SCREW_INSET },
+  ];
+}
+
 /** Threshold big on the left, makeup big on the right, the times and the shape small beside the meter. */
 export const PANEL_LAYOUT: PanelLayout = {
   title: { x: 34, y: 14, w: 220, h: 30 },
@@ -61,14 +71,24 @@ export const PANEL_LAYOUT: PanelLayout = {
     release: { x: 598, y: 205, size: SMALL_DIAL },
     makeup: { x: 712, y: 160, size: BIG_DIAL },
   },
-  screws: [
-    { x: SCREW_INSET, y: SCREW_INSET },
-    { x: PANEL.w - SCREW_INSET, y: SCREW_INSET },
-    { x: SCREW_INSET, y: PANEL.h - SCREW_INSET },
-    { x: PANEL.w - SCREW_INSET, y: PANEL.h - SCREW_INSET },
-  ],
+  screws: screwsOf(PANEL),
 };
 
+/** The Gain as a device (#384): an orange plate with one big knob. */
+export const GAIN_PANEL = { w: 160, h: 220 };
+
+export const GAIN_LAYOUT = {
+  title: { x: GAIN_PANEL.w / 2, y: 14 },
+  knob: { x: GAIN_PANEL.w / 2, y: 120, size: BIG_DIAL },
+  screws: screwsOf(GAIN_PANEL),
+};
+
+/**
+ * How the Gain's knob turns, from -120 to +24 dB: below 1 the loud end gets more of the turn, and
+ * 0.26 puts 0 dB straight up, so the quiet tail, which is all but silence, goes by quickly.
+ */
+export const GAIN_TAPER = 0.26;
+
 /** All a knob takes on the plate: its name above, its dial and its number below. */
 export function knobBox(spot: KnobSpot): Box {
   const w = Math.max(spot.size, KNOB_LEAST_WIDTH);

src/editor/soundfx/nodeFaces.ts

@@ -1,13 +1,15 @@
 import type { GraphNode } from '../../core/graph';
-import { SoundFxCompressor, SoundFxParametricEq } from '../../core/soundfx/nodes';
+import { SoundFxCompressor, SoundFxGain, SoundFxParametricEq } from '../../core/soundfx/nodes';
 import type { NodeFace } from '../graph/nodeFace';
 import type { EditorState } from '../state';
 import { CompressorFace } from './CompressorFace';
 import { EqFace } from './EqFace';
+import { GainFace } from './GainFace';
 
-/** The nodes drawn as a face of their own instead of rows (#380, #381), by type. */
+/** The nodes drawn as a face of their own instead of rows (#380, #381, #384), by type. */
 export function nodeFaceFor(state: EditorState, assetId: string, node: GraphNode): NodeFace | null {
   if (node.type === SoundFxCompressor.type) return new CompressorFace(state, assetId, node.id);
   if (node.type === SoundFxParametricEq.type) return new EqFace(state, assetId, node.id);
+  if (node.type === SoundFxGain.type) return new GainFace(state, assetId, node.id);
   return null;
 }

src/ui/widgets/Knob.ts

@@ -41,6 +41,8 @@ export interface KnobOptions extends KnobRange {
   format?: (value: number) => string;
   /** The shown number's colour, to stand on a panel's own plate. */
   ink?: number;
+  /** The colour of a chrome dial's value arc, when the plate is too near its orange (#384). */
+  arc?: number;
 }
 
 /** One for all chrome dials, laid over each cap's own bounds: light from the upper left. */
@@ -157,7 +159,7 @@ class Dial extends Widget {
     g.arc(x, y, track, angle(0), angle(1)).stroke({ color: 0x55595f, width: 3, alpha: 0.35 });
     if (at !== origin)
       g.arc(x, y, track, angle(Math.min(at, origin)), angle(Math.max(at, origin))).stroke({
-        color: this.knob.enabled ? CHROME_ARC : 0x8b8f95,
+        color: this.knob.enabled ? (this.knob.options.arc ?? CHROME_ARC) : 0x8b8f95,
         width: 3,
       });
     // The black skirt with its grip, the metal cap on it.
@@ -278,9 +280,9 @@ export class Knob extends VStack {
     return this.options.format?.(shown) ?? formatNumber(shown, this.options.decimals);
   }
 
-  /** Where the dial is on screen, for the check scripts. */
+  /** Where the dial's middle is on screen, for the check scripts; also in a zoomed graph (#384). */
   dialGlobal(): { x: number; y: number } {
-    const at = this.dial.getGlobalPosition();
-    return { x: at.x + this.dial.w / 2, y: at.y + this.dial.h / 2 };
+    const at = this.dial.toGlobal({ x: this.dial.w / 2, y: this.dial.h / 2 });
+    return { x: at.x, y: at.y };
   }
 }

tests/editor/hardware-view.test.ts

@@ -1,11 +1,15 @@
 /**
  * The Compressor's hardware panel (#379): every part on the plate and none over another, the meter's
- * scale and needle, the LEDs, and the grain of the plate the same every time.
+ * scale and needle, the LEDs, and the grain of the plate the same every time. The Gain's plate
+ * (#384) and how its one knob turns.
  */
 import { describe, expect, it } from 'vitest';
 import {
   type Box,
   brushStrokes,
+  GAIN_LAYOUT,
+  GAIN_PANEL,
+  GAIN_TAPER,
   gainReduction,
   knobBox,
   LED_COUNT,
@@ -21,6 +25,8 @@ import {
   PANEL,
   PANEL_LAYOUT,
 } from '../../src/editor/soundfx/hardwareView';
+import { GAIN_ROW } from '../../src/core/soundfx/nodes';
+import { knobPosition } from '../../src/ui/knob';
 
 const overlap = (a: Box, b: Box) => a.x < b.x + b.w && b.x < a.x + a.w && a.y < b.y + b.h && b.y < a.y + a.h;
 
@@ -129,3 +135,25 @@ describe('the LEDs', () => {
     expect(ledStep(-6, -Infinity, 10)).toBe(-11);
   });
 });
+
+describe('the Gain (#384)', () => {
+  const L = GAIN_LAYOUT;
+  const knob = knobBox(L.knob);
+
+  it('holds its knob inside the plate, clear of the screws and below the title', () => {
+    expect(knob.x).toBeGreaterThanOrEqual(0);
+    expect(knob.x + knob.w).toBeLessThanOrEqual(GAIN_PANEL.w);
+    expect(knob.y + knob.h).toBeLessThanOrEqual(GAIN_PANEL.h);
+    expect(knob.y).toBeGreaterThanOrEqual(L.title.y + 30);
+    expect(knob.x + knob.w / 2).toBe(GAIN_PANEL.w / 2);
+    for (const screw of L.screws)
+      expect(overlap(knob, { x: screw.x - 7, y: screw.y - 7, w: 14, h: 14 })).toBe(false);
+  });
+
+  it('turns 0 dB straight up and the quiet tail by in a fifth of the turn', () => {
+    const range = { min: GAIN_ROW.min ?? 0, max: GAIN_ROW.max ?? 0, step: 0.5, taper: GAIN_TAPER };
+    expect(knobPosition(0, range)).toBeCloseTo(0.5, 2);
+    expect(knobPosition(-24, range)).toBeLessThan(0.22);
+    expect(knobPosition(-6, range)).toBeGreaterThan(0.4);
+  });
+});

tools/e2e/34-sound.mjs

@@ -1026,6 +1026,56 @@ export async function sound(t) {
       hwBesideTab.seen.needle > 3,
     JSON.stringify({ hwTab, seen: hwBesideTab.seen }),
   );
+  // #384: a Gain node is drawn as an orange device with its one knob, worked as the Compressor's.
+  //       The Compressor's node is wide enough to lie over the Gain's: the Gain goes below it here.
+  const gainUnder = await json("__gm.compressor.panel('fx-hw').node");
+  await mutate(`
+    const graph = __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph;
+    graph.nodes.find((n) => n.id === 'fx-gain').y = 400;`);
+  await evaluate('__gm.soundfx.fit()');
+  await sleep(100);
+  const gainPanel = () => json("__gm.gain.panel('fx-gain')");
+  const gainShown = await gainPanel();
+  const gainRect = gainShown.rect;
+  const gainBeside = (p) => p.y > gainRect.y && p.y < gainRect.y + gainRect.h;
+  const gainDb = () =>
+    json(
+      `__gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph.nodes.find((n) => n.id === 'fx-gain').params.gain`,
+    );
+  const gainDial = gainShown.knob.dial;
+  await drag(gainDial.x, gainDial.y, gainDial.x, gainDial.y - 20);
+  const gainDragged = await gainDb();
+  await press('z', { ctrl: true });
+  const gainUndone = await gainDb();
+  await t.wheel(gainDial.x, gainDial.y, -100);
+  const gainWheeled = { db: await gainDb(), panel: await gainPanel() };
+  await evaluate('__gm.soundfx.fit()');
+  await sleep(100);
+  const gainRefit = (await gainPanel()).knob.dial;
+  await t.doubleClick(gainRefit.x, gainRefit.y);
+  const gainReset = { db: await gainDb(), docs: await json('__gm.documents()') };
+  await press('z', { ctrl: true });
+  check(
+    'a Gain node shows its panel with one knob between its ports; a drag turns it as one undo step, the wheel zooms the graph, a double-click resets it without a tab',
+    gainShown.shown &&
+      gainShown.size.w === 160 &&
+      gainShown.size.h === 220 &&
+      gainShown.knob.number === '-6' &&
+      gainShown.knob.enabled &&
+      Object.values(gainShown.inputs).length === 3 &&
+      Object.values(gainShown.inputs).every((p) => p.x < gainRect.x && gainBeside(p)) &&
+      Object.values(gainShown.outputs).every((p) => p.x > gainRect.x + gainRect.w && gainBeside(p)) &&
+      gainDragged > -6 &&
+      gainUndone === -6 &&
+      gainWheeled.db === -6 &&
+      gainWheeled.panel.rect.w > gainRect.w + 5 &&
+      gainReset.db === 0 &&
+      gainReset.docs.active === `asset:${fxId}`,
+    JSON.stringify({ gainUnder, gainShown, gainDragged, gainUndone, gainWheeled, gainReset }),
+  );
+  await mutate(`
+    const graph = __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph;
+    graph.nodes.find((n) => n.id === 'fx-gain').y = 0;`);
   await mutate(`
     const graph = __gm.state.project.assets.find((a) => a.id === ${JSON.stringify(fxId)}).graph;
     graph.nodes = graph.nodes.filter((n) => n.id !== 'fx-hw');