feuerwerk/tests/core/composition-edit.test.ts

/**
 * Editing a composition (#417): items of a track may overlap, clips may not – a dropped clip lands in
 * the gap it falls into –, the edges of an item go where they are dragged, its video's edges marked
 * and snapped to, and an item that follows its media is fitted to it again – in the same undo step –
 * when an override gives it another video.
 */
import { describe, expect, it } from 'vitest';
import { CreateAssetCommand, CreateVideoCommand } from '../../src/core/commands/assetCommands';
import {
  addCompositionItem,
  FitMediaCommand,
  pasteCompositionItems,
  removeCompositionTrack,
  removeFromComposition,
  SetCompositionCommand,
} from '../../src/core/commands/compositionCommands';
import { ClearOverrideCommand, SetOverrideCommand } from '../../src/core/commands/sceneObjectCommands';
import type { CompositionClip, CompositionItem } from '../../src/core/model/Asset';
import {
  carriedClips,
  clampedMove,
  droppedLength,
  droppedSpan,
  fadedItem,
  heldMove,
  type ItemMedia,
  mediaEdges,
  mediaMarks,
  movedClips,
  movedItems,
  movedWithClips,
  pastedClips,
  pastedItems,
  pastedItemsWithClips,
  resizedItem,
  snappedToMedia,
  trimmedItem,
} from '../../src/core/model/compositionEdit';
import { copyObjects } from '../../src/core/model/clipboard';
import {
  clipsInBand,
  hitAt,
  itemsInBand,
  overlaps,
  uncoveredEnd,
} from '../../src/editor/composition/compositionView';
import { fadeLevel, itemFades } from '../../src/core/model/composition';
import { placementRejection } from '../../src/core/model/placement';
import { findAsset, findAssetOf } from '../../src/core/model/Project';
import { makeProject } from '../helpers';

const FILE = `a1b2c3d4e5f6/${'c7'.repeat(32)}.mp4`;

const item = (
  id: string,
  track: string,
  start: number,
  length: number,
  extra: Partial<CompositionItem> = {},
) => ({ id, track, start, length, offset: 0, ...extra }) satisfies CompositionItem;

describe('a drop', () => {
  const taken = [
    { start: 60, length: 60 },
    { start: 200, length: 30 },
  ];

  it('lands where it is let go when that is free, as long as it is', () => {
    expect(droppedSpan(taken, 0, 50)).toEqual({ start: 0, length: 50 });
  });

  it('lands right after an item it falls on, and is cut short where the next begins', () => {
    expect(droppedSpan(taken, 90, 180)).toEqual({ start: 120, length: 80 });
  });

  it('is cut short before the item after the gap it lands in', () => {
    expect(droppedSpan(taken, 30, 180)).toEqual({ start: 30, length: 30 });
  });

  it('lands behind two items that touch when it falls on the first', () => {
    expect(
      droppedSpan(
        [
          { start: 0, length: 10 },
          { start: 10, length: 10 },
        ],
        5,
        60,
      ),
    ).toEqual({ start: 20, length: 60 });
  });
});

describe('moving', () => {
  const items = [item('a', 't1', 0, 60), item('b', 't1', 100, 60), item('c', 't2', 0, 60)];
  const tracks = ['t1', 't2'];

  it('moves the picked items by frames and tracks', () => {
    expect(movedItems(items, new Set(['a']), tracks, 30, 0)?.find((i) => i.id === 'a')?.start).toBe(30);
    expect(movedItems(items, new Set(['b']), tracks, 0, 1)?.find((i) => i.id === 'b')?.track).toBe('t2');
  });

  it('lets an item onto another, and refuses one before 0 or off the tracks', () => {
    expect(movedItems(items, new Set(['a']), tracks, 50, 0)?.map((i) => i.start)).toEqual([50, 100, 0]);
    expect(movedItems(items, new Set(['a']), tracks, 0, 1)?.map((i) => i.track)).toEqual(['t2', 't1', 't2']);
    expect(movedItems(items, new Set(['b']), tracks, -150, 0)).toBeNull();
    expect(movedItems(items, new Set(['c']), tracks, 0, 1)).toBeNull();
  });

  it('holds a move at frame 0 and the tracks there are, as far as the pointer goes', () => {
    expect(clampedMove(items, new Set(['b']), tracks, -150, 0)).toEqual({ frames: -100, tracks: 0 });
    expect(clampedMove(items, new Set(['a', 'c']), tracks, 20, 1)).toEqual({ frames: 20, tracks: 0 });
    expect(clampedMove(items, new Set(['a']), tracks, 0, -3)).toEqual({ frames: 0, tracks: 0 });
  });

  it('lets a picked item go where another picked one was', () => {
    const moved = movedItems(items, new Set(['a', 'b']), tracks, 40, 0);
    expect(moved?.map((i) => i.start)).toEqual([40, 140, 0]);
  });

  it('keeps clips of a track apart by their own lengths', () => {
    const clips: CompositionClip[] = [
      { id: 'x', track: 't1', animation: 'm', start: 0 },
      { id: 'y', track: 't1', animation: 'm', start: 50 },
    ];
    const lengthOf = () => 40;
    expect(movedClips(clips, new Set(['x']), tracks, 5, 0, lengthOf)).not.toBeNull();
    expect(movedClips(clips, new Set(['x']), tracks, 20, 0, lengthOf)).toBeNull();
  });
});

const clip = (id: string, track: string, start: number) =>
  ({ id, track, animation: 'anim', start }) satisfies CompositionClip;

describe('clips that go with their item', () => {
  const tracks = ['t1', 't2'];
  // Every clip is 10 frames long.
  const lengthOf = () => 10;

  it('belong to the item at their first frame, of two there the one in front', () => {
    const items = [item('a', 't1', 0, 60), item('b', 't1', 40, 60), item('c', 't1', 40, 10)];
    // `x` starts in `a` alone; `y` where `a`, `b` and `c` lie – `c`, the later in the list, is in
    // front; `z` starts before `b` and only reaches into it, so it stays with `a`.
    const clips = [clip('x', 't1', 10), clip('y', 't1', 45), clip('z', 't1', 35), clip('w', 't2', 10)];
    expect([...carriedClips(items, clips, new Set(['a']))]).toEqual(['x', 'z']);
    expect([...carriedClips(items, clips, new Set(['b']))]).toEqual([]);
    expect([...carriedClips(items, clips, new Set(['c']))]).toEqual(['y']);
    // One past an item's end it is not the item's any more.
    expect([...carriedClips(items, [clip('v', 't1', 100)], new Set(['b']))]).toEqual([]);
  });

  it('move with their item, also onto another track; with Alt they stay', () => {
    const items = [item('a', 't1', 0, 60), item('b', 't2', 0, 60)];
    const clips = [clip('x', 't1', 10), clip('y', 't2', 50)];
    const moved = movedWithClips(items, clips, new Set(['a']), tracks, 5, 1, lengthOf)!;
    expect(moved.items[0]).toMatchObject({ start: 5, track: 't2' });
    expect(moved.clips).toEqual([clip('x', 't2', 15), clip('y', 't2', 50)]);
    const alone = movedWithClips(items, clips, new Set(['a']), tracks, 5, 1, lengthOf, true)!;
    expect(alone.clips).toEqual(clips);
  });

  it('hold the move short of another clip, the item with them', () => {
    const items = [item('a', 't1', 0, 60)];
    const clips = [clip('x', 't1', 10), clip('y', 't1', 70)];
    const picked = new Set(['a']);
    const fits = (by: number) => movedWithClips(items, clips, picked, tracks, by, 0, lengthOf) !== null;
    // `x` at 10 + 55 would lie over `y` (70–80): the move stops where `x` ends right at 70.
    expect(movedWithClips(items, clips, picked, tracks, 55, 0, lengthOf)).toBeNull();
    expect(heldMove({ frames: 55, tracks: 0 }, { frames: 0, tracks: 0 }, fits)).toEqual({
      frames: 50,
      tracks: 0,
    });
    // Past `y` it fits again.
    expect(heldMove({ frames: 70, tracks: 0 }, { frames: 0, tracks: 0 }, fits)).toEqual({
      frames: 70,
      tracks: 0,
    });
  });

  it('are pasted with their items, all moved on until the clips lie apart', () => {
    const items = [item('a', 't1', 20, 60)];
    const copied = [clip('x', 't1', 30)];
    const ids = new Map([
      ['a', 'a2'],
      ['x', 'x2'],
    ]);
    // Landing at 100, `x2` would start at 110, over `y` (105–115): both move on by 5.
    const out = pastedItemsWithClips(items, copied, [clip('y', 't1', 105)], ids, 100, tracks, lengthOf);
    expect(out.items).toEqual([item('a2', 't1', 105, 60)]);
    expect(out.clips).toEqual([clip('x2', 't1', 115)]);
  });
});

describe('the edges of an item', () => {
  const b = item('b', 't1', 100, 60, { fitMedia: true, offset: 1 });

  it('a dragged end goes where it is let go, at least a frame, and the length is the item’s own from then on', () => {
    expect(resizedItem(b, 500)).toEqual({ id: 'b', track: 't1', start: 100, length: 500, offset: 1 });
    expect(resizedItem(b, 0).length).toBe(1);
  });

  it('a dragged start moves where the video begins with it', () => {
    const trimmed = trimmedItem(b, 130, 60, true);
    expect([trimmed.start, trimmed.length, trimmed.offset, trimmed.fitMedia]).toEqual([
      130,
      30,
      1.5,
      undefined,
    ]);
    expect(trimmedItem(b, 10, 60, false)).toMatchObject({ start: 10, length: 150, offset: 1 });
    expect(trimmedItem(b, 500, 60, false).start).toBe(159);
  });

  it('with a video, a dragged start goes on before the video’s beginning, the offset below 0', () => {
    // One second into its video: back a second the video begins with the item, back 1.5 s half a second after it.
    expect(trimmedItem(b, 40, 60, true)).toMatchObject({ start: 40, length: 120, offset: 0 });
    expect(trimmedItem(b, 10, 60, true)).toMatchObject({ start: 10, length: 150, offset: -0.5 });
    expect(trimmedItem(b, -20, 60, true).start).toBe(0);
  });
});

describe('the video of an item on the timeline', () => {
  // A 2 s video at 60 fps that began at frame 40: the item from 100 is one second in.
  const once: ItemMedia = { begins: 40, length: 120, loops: false };
  const round: ItemMedia = { ...once, loops: true };

  it('has its edges where it begins and each pass ends, round only when it loops', () => {
    expect(mediaEdges(once, 0, 1000)).toEqual([40, 160]);
    expect(mediaEdges(round, 100, 500)).toEqual([160, 280, 400]);
    expect(mediaEdges(round, 0, 30)).toEqual([]);
  });

  it('marks an end cutting into the video, and a line where the item reaches past it', () => {
    expect(mediaMarks(item('i', 't', 100, 30), once)).toEqual({ seams: [], cutStart: true, cutEnd: true });
    expect(mediaMarks(item('i', 't', 40, 120), once)).toEqual({ seams: [], cutStart: false, cutEnd: false });
    expect(mediaMarks(item('i', 't', 20, 200), once)).toEqual({
      seams: [40, 160],
      cutStart: false,
      cutEnd: false,
    });
    expect(mediaMarks(item('i', 't', 100, 200), round).seams).toEqual([160, 280]);
  });

  it('pulls a dragged edge onto the video’s within reach, and leaves it alone further off', () => {
    expect(snappedToMedia(157, once, 4)).toBe(160);
    expect(snappedToMedia(150, once, 4)).toBe(150);
    expect(snappedToMedia(42, null, 4)).toBe(42);
  });
});

describe('overlapping items on the timeline', () => {
  const view = { panX: 0, pxPerTick: 2, panY: 0, trackHeight: 48 };
  const tracks = [{ id: 't1', name: 'Track 1' }];
  // `late` covers `early` from frame 50 on; on screen the overlap runs from x 100 to 120.
  const early = item('early', 't1', 0, 60);
  const late = item('late', 't1', 50, 60);
  const hit = (x: number) => hitAt(view, tracks, [late, early], [], () => 0, { x, y: 20 });

  it('takes the end of the one covered, the body of the one on top', () => {
    expect(hit(119)).toEqual({ kind: 'item', id: 'early', part: 'end' });
    expect(hit(110)).toEqual({ kind: 'item', id: 'late', part: 'body' });
    expect(hit(101)).toEqual({ kind: 'item', id: 'late', part: 'start' });
    expect(hit(40)).toEqual({ kind: 'item', id: 'early', part: 'body' });
  });

  it('knows where they overlap and how much of the earlier one is seen', () => {
    expect(overlaps([late, early])).toEqual([{ track: 't1', start: 50, end: 60 }]);
    expect(overlaps([early, item('other', 't2', 0, 60)])).toEqual([]);
    expect(uncoveredEnd([late, early], early)).toBe(50);
    expect(uncoveredEnd([late, early], late)).toBe(110);
  });
});

function makeCut() {
  const f = makeProject();
  const comp = new CreateAssetCommand('composition', 'Cut');
  const box = new CreateAssetCommand('sprite', 'Box');
  const video = new CreateVideoCommand('Intro', FILE, {
    width: 320,
    height: 180,
    duration: 5,
    fps: 30,
    audio: false,
  });
  f.stack.execute(comp);
  f.stack.execute(box);
  f.stack.execute(video);
  const current = () => findAssetOf(f.project, comp.asset.id, 'composition')!;
  const track = current().tracks[0]!.id;
  /** An item of the box, run through the stack as the timeline does it. */
  const add = (start: number, length: number, assetId = box.asset.id) => {
    const { command, objectId } = addCompositionItem(f.project, comp.asset.id, assetId, {
      track,
      start,
      length,
      offset: 0,
      fitMedia: true,
    });
    f.stack.execute(command);
    return objectId;
  };
  return {
    ...f,
    compId: comp.asset.id,
    boxId: box.asset.id,
    videoId: video.asset.id,
    comp: current,
    track,
    add,
  };
}

describe('items and their objects', () => {
  it('an item comes with its object in one undo step, and goes with it', () => {
    const cut = makeCut();
    const id = cut.add(0, 180);
    expect(cut.comp().objects.map((o) => o.id)).toEqual([id]);
    expect(cut.comp().items.map((i) => i.id)).toEqual([id]);
    cut.stack.execute(removeFromComposition(cut.project, cut.compId, [id], []));
    expect([cut.comp().objects, cut.comp().items]).toEqual([[], []]);
    cut.stack.undo();
    expect(cut.comp().items.map((i) => i.id)).toEqual([id]);
    cut.stack.undo();
    expect([cut.comp().objects, cut.comp().items]).toEqual([[], []]);
  });

  it('a track goes with what lies on it, and the last track stays', () => {
    const cut = makeCut();
    const second = { id: 't2', name: 'Track 2' };
    cut.stack.execute(new SetCompositionCommand(cut.compId, { tracks: [...cut.comp().tracks, second] }));
    cut.add(0, 60);
    cut.stack.execute(removeCompositionTrack(cut.project, cut.compId, cut.track));
    expect(cut.comp().tracks.map((t) => t.id)).toEqual(['t2']);
    expect([cut.comp().objects, cut.comp().items]).toEqual([[], []]);
    cut.stack.execute(removeCompositionTrack(cut.project, cut.compId, 't2'));
    expect(cut.comp().tracks).toHaveLength(1);
  });

  it('a composition cannot be placed into a composition', () => {
    const cut = makeCut();
    expect(placementRejection(cut.project, cut.comp(), findAsset(cut.project, cut.compId)!)).not.toBe('');
  });

  it('pasted items keep their timing from the frame they land at, on their tracks or shifted to a row', () => {
    const copied = [item('a', 't2', 30, 60, { offset: 1.5 }), item('b', 't3', 50, 20)];
    const ids = new Map([
      ['a', 'a2'],
      ['b', 'b2'],
    ]);
    const tracks = ['t1', 't2', 't3'];
    expect(pastedItems(copied, ids, 100, tracks)).toEqual([
      item('a2', 't2', 100, 60, { offset: 1.5 }),
      item('b2', 't3', 120, 20),
    ]);
    expect(pastedItems(copied, ids, 0, tracks, 0).map((i) => i.track)).toEqual(['t1', 't2']);
    // As far as there are tracks: the bottom one may not fall off.
    expect(pastedItems(copied, ids, 0, tracks, 2).map((i) => i.track)).toEqual(['t2', 't3']);
  });

  it('pasted clips keep their timing and move on until none lies over another clip', () => {
    const clip = (id: string, track: string, start: number) =>
      ({ id, track, animation: 'anim', start }) satisfies CompositionClip;
    // Every clip is 10 frames long.
    const lengthOf = () => 10;
    const tracks = ['t1', 't2'];
    const copied = [clip('a', 't1', 0), clip('b', 't2', 15)];
    const ids = new Map([
      ['a', 'a2'],
      ['b', 'b2'],
    ]);
    // Room where they land: there they stay.
    expect(pastedClips(copied, [clip('x', 't1', 50)], ids, 30, tracks, lengthOf)).toEqual([
      clip('a2', 't1', 30),
      clip('b2', 't2', 45),
    ]);
    // `a2` at 45 would lie over `x` (50–60), `b2` over `y` (60–70): `a2` waits until 60, `b2` comes along.
    const taken = [clip('x', 't1', 50), clip('y', 't2', 60)];
    expect(pastedClips(copied, taken, ids, 45, tracks, lengthOf)).toEqual([
      clip('a2', 't1', 60),
      clip('b2', 't2', 75),
    ]);
    // Onto the clips they were copied from, they go right behind them, shifted to a row as far as it goes.
    expect(pastedClips([clip('a', 't1', 0)], [clip('a', 't1', 0)], ids, 0, tracks, lengthOf, 1)).toEqual([
      clip('a2', 't2', 0),
    ]);
    expect(pastedClips([clip('a', 't1', 0)], [clip('a', 't1', 0)], ids, 0, tracks, lengthOf)).toEqual([
      clip('a2', 't1', 10),
    ]);
  });

  it('a band picks the items and clips it touches', () => {
    const view = { panX: 0, pxPerTick: 1, panY: 0, trackHeight: 40 };
    const tracks = [
      { id: 't1', name: 'One' },
      { id: 't2', name: 'Two' },
    ];
    const items = [item('a', 't1', 0, 50), item('b', 't1', 100, 50), item('c', 't2', 0, 50)];
    const clips = [{ id: 'k', track: 't2', animation: 'anim', start: 20 }];
    // Across the first track, from 40 to 60: only `a` reaches in.
    expect(itemsInBand(view, tracks, items, { x: 40, y: 5 }, { x: 60, y: 30 })).toEqual(['a']);
    // Down over both tracks at the start, drawn from bottom right to top left.
    expect(itemsInBand(view, tracks, items, { x: 10, y: 70 }, { x: 5, y: 10 })).toEqual(['a', 'c']);
    // Clips lie in the lower part of their track: a band through its upper part misses them.
    expect(clipsInBand(view, tracks, clips, () => 10, { x: 0, y: 42 }, { x: 60, y: 50 })).toEqual([]);
    expect(clipsInBand(view, tracks, clips, () => 10, { x: 0, y: 42 }, { x: 60, y: 70 })).toEqual(['k']);
  });

  it('a copied item is pasted with its object and overrides under new ids, in one undo step', () => {
    const cut = makeCut();
    const id = cut.add(10, 60);
    cut.stack.execute(new SetOverrideCommand(cut.compId, id, 'width', 42));
    const clip = copyObjects(cut.project, cut.comp(), [id])!;
    const pasted = pasteCompositionItems(cut.project, cut.compId, clip, 100)!;
    cut.stack.execute(pasted.command);
    const [copy] = pasted.itemIds;
    expect(copy).not.toBe(id);
    expect(cut.comp().items.find((i) => i.id === copy)).toMatchObject({
      track: cut.track,
      start: 100,
      length: 60,
    });
    expect(cut.comp().objects.find((o) => o.id === copy)?.overrides).toMatchObject({ width: 42 });
    cut.stack.undo();
    expect(cut.comp().items.map((i) => i.id)).toEqual([id]);
    expect(cut.comp().objects.map((o) => o.id)).toEqual([id]);
  });

  it('objects without their items, as a scene copies them, are not pasted into a composition', () => {
    const cut = makeCut();
    const id = cut.add(0, 60);
    const { items, ...plain } = copyObjects(cut.project, cut.comp(), [id])!;
    expect(items).toHaveLength(1);
    expect(pasteCompositionItems(cut.project, cut.compId, plain, 0)).toBeNull();
  });

  it('a deleted item takes its clips with it, in the same undo step', () => {
    const cut = makeCut();
    const a = cut.add(0, 60);
    const b = cut.add(60, 60);
    const clips = [clip('mine', cut.track, 10), clip('next', cut.track, 70)];
    cut.stack.execute(new SetCompositionCommand(cut.compId, { clips }));
    cut.stack.execute(removeFromComposition(cut.project, cut.compId, [a], []));
    expect(cut.comp().items.map((i) => i.id)).toEqual([b]);
    expect(cut.comp().clips.map((c) => c.id)).toEqual(['next']);
    cut.stack.undo();
    expect(cut.comp().clips.map((c) => c.id)).toEqual(['mine', 'next']);
  });

  it('a copied item is pasted with its clips under new ids, moved on with them where a clip lies', () => {
    const cut = makeCut();
    const a = cut.add(0, 60);
    cut.stack.execute(new SetCompositionCommand(cut.compId, { clips: [clip('mine', cut.track, 10)] }));
    const copy = copyObjects(cut.project, cut.comp(), [a])!;
    expect(copy.clips?.map((c) => c.id)).toEqual(['mine']);
    // Its animation is not there, so the clip is a frame long. Landing at 0 the copy of the clip
    // would lie right over `mine`: item and clip move on by a frame.
    const pasted = pasteCompositionItems(cut.project, cut.compId, copy, 0)!;
    cut.stack.execute(pasted.command);
    const [b] = pasted.itemIds;
    expect(cut.comp().items.find((i) => i.id === b)?.start).toBe(1);
    const added = cut.comp().clips.filter((c) => c.id !== 'mine');
    expect(added).toHaveLength(1);
    expect(added[0]).toMatchObject({ track: cut.track, animation: 'anim', start: 11 });
    cut.stack.undo();
    expect(cut.comp().clips.map((c) => c.id)).toEqual(['mine']);
  });

  it('a sprite wearing a video is dropped in as long as the video, anything else 3 s', () => {
    const cut = makeCut();
    const screen = new CreateAssetCommand('sprite', 'Screen', { texture: cut.videoId });
    cut.stack.execute(screen);
    expect(droppedLength(cut.project, cut.comp(), screen.asset)).toBe(300);
    expect(droppedLength(cut.project, cut.comp(), findAsset(cut.project, cut.boxId)!)).toBe(180);
  });
});

describe('an item that follows its media (fitMedia)', () => {
  const wear = (cut: ReturnType<typeof makeCut>, id: string, texture: string) =>
    cut.stack.execute(new FitMediaCommand(new SetOverrideCommand(cut.compId, id, 'texture', texture)));

  it('takes the length of a video an override gives it, in the same undo step', () => {
    const cut = makeCut();
    const id = cut.add(0, 180);
    wear(cut, id, cut.videoId);
    expect(cut.comp().items[0]!.length).toBe(300);
    cut.stack.undo();
    expect(cut.comp().items[0]!.length).toBe(180);
    expect(cut.comp().objects[0]!.overrides.texture).toBeUndefined();
    cut.stack.redo();
    expect(cut.comp().items[0]!.length).toBe(300);
  });

  it('goes back to 3 s when the video is taken off again', () => {
    const cut = makeCut();
    const id = cut.add(0, 180);
    wear(cut, id, cut.videoId);
    expect(cut.comp().items[0]!.length).toBe(300);
    cut.stack.execute(new FitMediaCommand(new ClearOverrideCommand(cut.compId, id, 'texture')));
    expect(cut.comp().items[0]!.length).toBe(180);
  });

  it('runs on over the next item of its track, which stays where it is', () => {
    const cut = makeCut();
    const id = cut.add(0, 180);
    const next = cut.add(240, 60);
    wear(cut, id, cut.videoId);
    expect(cut.comp().items.map((i) => [i.id, i.start, i.length])).toEqual([
      [id, 0, 300],
      [next, 240, 60],
    ]);
  });

  it('is left alone once its length is its own', () => {
    const cut = makeCut();
    const id = cut.add(0, 180);
    const items = cut.comp().items.map((i) => resizedItem(i, 90));
    cut.stack.execute(new SetCompositionCommand(cut.compId, { items }));
    wear(cut, id, cut.videoId);
    expect(cut.comp().items[0]!.length).toBe(90);
  });
});

describe('the fades of an item (#418)', () => {
  const sound = item('a', 't1', 100, 60, { fadeIn: 10, fadeOut: 20 });

  it('go where their handle is dragged, no further than the other fade, and none at the edge', () => {
    expect(fadedItem(sound, 'in', 130).fadeIn).toBe(30);
    expect(fadedItem(sound, 'in', 150).fadeIn).toBe(40);
    expect('fadeIn' in fadedItem(sound, 'in', 90)).toBe(false);
    expect(fadedItem(sound, 'out', 150.4).fadeOut).toBe(10);
    expect(fadedItem(sound, 'out', 100).fadeOut).toBe(50);
    expect('fadeOut' in fadedItem(sound, 'out', 170)).toBe(false);
  });

  it('shape the level along their curves, silent at the very edges', () => {
    expect(fadeLevel(sound, 0)).toBe(0);
    expect(fadeLevel(sound, 5)).toBeCloseTo(0.5, 9);
    expect(fadeLevel(sound, 30)).toBe(1);
    expect(fadeLevel(sound, 50)).toBeCloseTo(0.5, 9);
    expect(fadeLevel({ ...sound, curveIn: 'equalPower' }, 5)).toBeCloseTo(Math.SQRT1_2, 9);
    expect(fadeLevel(item('b', 't1', 0, 60), 0)).toBe(1);
  });

  it('are taken by their handles on the top edge, before the item’s ends', () => {
    const view = { panX: 0, pxPerTick: 2, panY: 0, trackHeight: 48 };
    const tracks = [{ id: 't1', name: 'Track 1' }];
    const fades = (i: CompositionItem) => (i.id === 'a' ? itemFades(i) : null);
    const hit = (x: number, y: number, list = [sound]) =>
      hitAt(view, tracks, list, [], () => 0, { x, y }, fades);
    // The item runs from x 200 to 320; its fade in ends at 220, its fade out starts at 280.
    expect(hit(222, 4)).toEqual({ kind: 'item', id: 'a', part: 'fadeIn' });
    expect(hit(278, 10)).toEqual({ kind: 'item', id: 'a', part: 'fadeOut' });
    expect(hit(222, 30)).toEqual({ kind: 'item', id: 'a', part: 'body' });
    expect(hit(250, 4)).toEqual({ kind: 'item', id: 'a', part: 'body' });
    // Without fades the handles sit on the corners; lower down the corner is the edge.
    const plain = item('a', 't1', 100, 60);
    expect(hit(202, 4, [plain])).toEqual({ kind: 'item', id: 'a', part: 'fadeIn' });
    expect(hit(202, 30, [plain])).toEqual({ kind: 'item', id: 'a', part: 'start' });
    // An item without sound has none.
    expect(hit(202, 4, [item('b', 't1', 100, 60)])).toEqual({ kind: 'item', id: 'b', part: 'start' });
  });
});