feuerwerk/tools/e2e/28-shader.mjs

import { colourDistance } from '../lib/harness.mjs';
import { FIND_HALVES, HALVES_LEFT as LEFT, HALVES_RIGHT as RIGHT, PASTE_HALVES } from './lib/pictures.mjs';

/**
 * Shader assets: made from the + menu, built from nodes in the Shader tab, worn by a sprite through
 * its Shader dropdown – whose Property nodes are the rows below it – and visible in the pixels, in
 * the scene view and in the game. The fixture ships "Adjust colors"; the step removes what it made.
 */

/** (64, 128, 255): three distinct channels, so brightness, contrast and saturation each read differently. */
const BASE = '#4080ff';
const ADJUST = 'adjust-colors';

export async function shader(t) {
  const {
    check,
    sleep,
    json,
    evaluate,
    mutate,
    drag,
    click,
    clickText,
    locate,
    press,
    select,
    undo,
    play,
    stop,
    shot,
  } = t;
  const { doubleClick, typeText } = t;
  const field = (label) => json(`__gm.inspectorField(${JSON.stringify(label)})`);
  const info = () => json('__gm.shader.info()');
  const shaders = () =>
    json(`__gm.state.project.assets
      .filter((a) => a.type === 'shader')
      .map((a) => ({ id: a.id, name: a.name, nodes: a.graph.nodes.map((n) => ({ id: n.id, type: n.type, name: n.params.name })) }))`);
  /** The overlay is drawn last, so a menu entry wins over a tab button or a row saying the same. */
  const clickLast = async (text) => {
    const p = await locate(text, true);
    await click(p.x, p.y);
    await sleep(200);
  };
  const assetProps = (patch) =>
    mutate(
      `Object.assign(__gm.state.project.assets.find((a) => a.id === 'shade-sprite').props, ${JSON.stringify(patch)})`,
    );

  await press('Escape');
  await evaluate('document.activeElement instanceof HTMLElement && document.activeElement.blur()');
  await evaluate('__gm.state.select(null)');
  await sleep(200);

  // 28a. The fixture ships Adjust colors as an asset; the + menu makes another and opens its tab on it.
  const seeded = (await shaders()).find((s) => s.id === ADJUST);
  check(
    'the fixture carries the Adjust colors shader as an asset of twelve nodes',
    Boolean(seeded) && seeded.nodes.length === 12,
    JSON.stringify(seeded),
  );
  await clickText('+');
  await sleep(200);
  await clickLast('Shader');
  await sleep(400);
  const made = (await shaders()).find((s) => s.id !== ADJUST);
  const selection = await json('__gm.state.selection');
  check(
    'the + menu creates a shader asset, selected, and its tab opens on it',
    Boolean(made) &&
      selection?.kind === 'asset' &&
      selection.assetId === made.id &&
      (await json('__gm.tab()')) === 'shader' &&
      (await json('__gm.shader.current()')) === made.id,
    JSON.stringify({ made, selection, tab: await json('__gm.tab()') }),
  );
  if (!made) return;
  check('the tab button has room for its label', (await json("__gm.shownLabel('Shader')")) === 'Shader');
  // Named after its type, the asset's row in the Assets panel would say "Shader" like the inspector row.
  await mutate(`__gm.state.project.assets.find((a) => a.id === ${JSON.stringify(made.id)}).name = 'Glow'`);
  made.name = 'Glow';
  check('an empty shader says what it lacks', (await info()) === 'No Output node', await info());

  // 28b. Right-click offers shader nodes only; Texture color and Output placed from the palette.
  const canvas = await json('__gm.shader.canvasRect()');
  await click(canvas.x + 80, canvas.y + 60, 'right');
  await sleep(300);
  const offered = await json('__gm.overlayTexts()');
  check(
    'right-click offers shader nodes and no behavior node',
    ['Texture color', 'Output', 'Property', 'Number', 'Mix', 'Luminance'].every((text) =>
      offered.includes(text),
    ) && !offered.some((text) => /On start|Boolean|Branch|Set state/.test(text)),
    JSON.stringify(offered),
  );
  // A dozen entries scroll; searched, the row is the only one and in view.
  await typeText('Texture color');
  await sleep(150);
  await clickLast('Texture color');
  await sleep(300);
  await click(canvas.x + 420, canvas.y + 60, 'right');
  await sleep(300);
  await clickLast('Output');
  await sleep(300);
  const madeNodes = async () => (await shaders()).find((s) => s.id === made.id)?.nodes ?? [];
  check(
    'both nodes are in the graph, the Output where its right-click was',
    (await madeNodes()).map((n) => n.type).join(',') === 'ShaderTextureColor,ShaderOutput',
    JSON.stringify(await madeNodes()),
  );
  await click(canvas.x + 420, canvas.y + 320, 'right');
  await sleep(300);
  const again = await json('__gm.overlayTexts()');
  check(
    'the palette offers the Output only once',
    !again.includes('Output') && again.includes('Property'),
    JSON.stringify(again),
  );
  await press('Escape');
  await sleep(200);
  check(
    'an Output with nothing connected compiles: the texel passes through, no property declared',
    (await info()) === '0 properties',
    await info(),
  );

  // 28c. A Property node: its name is the row a sprite shows; a bad name is a problem on the node.
  await click(canvas.x + 80, canvas.y + 320, 'right');
  await sleep(300);
  // Property is the twelfth entry, below the palette's scroll mask: search it into view first.
  await typeText('Property');
  await sleep(150);
  await clickLast('Property');
  await sleep(300);
  const propertyNode = (await madeNodes()).find((n) => n.type === 'ShaderProperty');
  check(
    'the placed property is named "value" and counted',
    propertyNode?.name === 'value' && (await info()) === '1 property',
    JSON.stringify({ propertyNode, info: await info() }),
  );
  const nameField = await json("__gm.inspectorField('Name', true)");
  check('the inspector shows a Name field for the property', Boolean(nameField), JSON.stringify(nameField));
  await doubleClick(nameField.x, nameField.y);
  await typeText('glow');
  await press('Enter');
  await sleep(300);
  check(
    'typing in the Name field renames the property, on the node too',
    (await madeNodes()).find((n) => n.id === propertyNode?.id)?.name === 'glow' &&
      (await json(`__gm.shader.nodeLabel(${JSON.stringify(propertyNode?.id)})`)) === 'glow',
    JSON.stringify(await madeNodes()),
  );
  await shot('28-shader-tab');
  await mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    a.graph.nodes.find((n) => n.id === ${JSON.stringify(propertyNode?.id)}).params.name = 'no good';`);
  await sleep(300);
  const problem = await json(`__gm.shader.nodeProblem(${JSON.stringify(propertyNode?.id)})`);
  check(
    'a name that is not one word is a problem on the node and the reason in the readout',
    typeof problem === 'string' && problem.startsWith('Name must be') && (await info()) === problem,
    JSON.stringify({ problem, info: await info() }),
  );
  await mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    a.graph.nodes.find((n) => n.id === ${JSON.stringify(propertyNode?.id)}).params.name = 'glow';`);
  await sleep(300);

  // 28c-ii. Where a node sits is the editor's business: dropping it somewhere else compiles nothing
  //         again, a changed param does – once (#65).
  const nodeRef = JSON.stringify(propertyNode?.id);
  const compiledBefore = await json('__gm.shaderCompiles()');
  const grab = await json(`__gm.shader.nodeAt(${nodeRef})`);
  await drag(grab.x, grab.y, grab.x + 60, grab.y + 40);
  await sleep(300);
  const dropped = await json(`__gm.shader.nodeAt(${nodeRef})`);
  const compiledAfterMove = await json('__gm.shaderCompiles()');
  check(
    'dropping a node somewhere else moves it without compiling the graph again',
    dropped.x > grab.x + 30 && compiledAfterMove === compiledBefore,
    JSON.stringify({ grab, dropped, compiledBefore, compiledAfterMove }),
  );
  const defaultBefore = await json(
    `__gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)}).graph.nodes.find((n) => n.id === ${nodeRef}).params.default`,
  );
  const setDefault = (value) =>
    mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    a.graph.nodes.find((n) => n.id === ${nodeRef}).params.default = ${JSON.stringify(value)};`);
  await setDefault(2);
  await sleep(300);
  const compiledAfterParam = await json('__gm.shaderCompiles()');
  check(
    'changing a param compiles it again, once',
    compiledAfterParam === compiledAfterMove + 1,
    JSON.stringify({ compiledAfterMove, compiledAfterParam }),
  );
  await setDefault(defaultBefore);
  await sleep(300);

  // 28d. A flat sprite on the camera, drawn on top of everything; its Shader dropdown lists the assets.
  await mutate(`
    const project = __gm.state.project;
    const sprite = structuredClone(project.assets.find((a) => a.id === 'crate'));
    sprite.id = 'shade-sprite';
    sprite.name = 'Shaded';
    sprite.props = { ...sprite.props, width: 160, height: 120, color: 0x4080ff, texture: '', shader: '' };
    project.assets.push(sprite);
    const scene = __gm.state.activeScene;
    const cam = scene.objects.find((o) => o.id === 'o3').position;
    scene.objects.push({ id: 'oshade', assetId: 'shade-sprite', name: '', position: { x: cam.x + 180, y: cam.y + 100, z: 950 }, editorOffset: { x: 0, y: 0 }, overrides: {}, parentId: '', instanceEdits: {} });
    __gm.state.select(null)`);
  await sleep(600);
  // The pixels are the scene view's; the tab is still the shader's.
  await evaluate("__gm.showTab('scene')");
  await select({ kind: 'object', holderId: 'scene1', objectIds: ['oshade'], objectId: 'oshade' });
  await sleep(400);
  const box = await json("__gm.objectRect('oshade')");
  check('the shaded sprite is on screen', Boolean(box) && box.w > 8, JSON.stringify(box));
  if (!box) return;
  const sample = (fx, fy) =>
    json(`__gm.pixelAt(${Math.round(box.x + fx * box.w)}, ${Math.round(box.y + fy * box.h)})`);
  // Off centre: a symbol may sit on the sprite's middle, and symbols draw above objects.
  const centre = () => sample(0.3, 0.3);
  const base = await centre();
  check('with no shader the sprite is its plain colour', colourDistance(base, BASE) < 12, base);

  // Every later check reads pixels at its own spot on this sprite, so nothing may be drawn over it.
  // The step parks the sprite away from the camera for that reason: symbols draw above objects, and
  // by this point the earlier steps have left containers and colliders around the origin. Without
  // this guard their outlines show up as a wrong colour in whichever check happens to sample them.
  const dirty = [];
  for (let fx = -0.4; fx <= 0.401; fx += 0.1)
    for (let fy = -0.4; fy <= 0.401; fy += 0.1) {
      const seen = await sample(fx, fy);
      if (colourDistance(seen, BASE) >= 12) dirty.push(`${fx.toFixed(1)},${fy.toFixed(1)}:${seen}`);
    }
  check('nothing is drawn over the sprite the pixel checks read', dirty.length === 0, dirty.join(' '));
  // The Shader row's dropdown reads "None"; it is the last such text in the inspector (Parent and
  // Texture say it above). The label itself is no anchor: the tab button says "Shader" too.
  const shaderField = await locate('None', true);
  check(
    'a sprite has a Shader row reading None, and no shader brings no parameter rows',
    shaderField.x > box.x + box.w && (await field('brightness')) === null,
    JSON.stringify(shaderField),
  );
  await click(shaderField.x, shaderField.y);
  await sleep(300);
  const choices = await json('__gm.overlayTexts()');
  check(
    'the dropdown offers None and every shader asset',
    choices.some((text) => text.includes('None')) &&
      choices.some((text) => text.includes('Adjust colors')) &&
      choices.some((text) => text.includes(made.name)),
    JSON.stringify({ choices, shaderField }),
  );
  await clickLast(choices.find((text) => text.includes('Adjust colors')));
  await sleep(400);
  const rows = await Promise.all([field('brightness'), field('contrast'), field('saturation')]);
  check(
    'picking Adjust colors adds its three property rows below the dropdown',
    rows.every((r) => r !== null) &&
      (await json("__gm.state.activeScene.objects.find((o) => o.id === 'oshade').overrides.shader")) ===
        ADJUST,
    JSON.stringify(rows),
  );
  await shot('28-shader-rows');
  await undo();
  await sleep(300);
  check('undoing the choice takes the rows away again', (await field('brightness')) === null);
  await select(null);
  await sleep(200);

  // 28e. Each property is visible in the pixels, with 1 neutral.
  await assetProps({ shader: ADJUST });
  await sleep(300);
  const neutral = await centre();
  check(
    'Adjust colors at its defaults draws exactly what no shader draws',
    colourDistance(neutral, base) < 6,
    JSON.stringify({ base, neutral }),
  );
  // What the cost was made of (#67) and is not any more (#77): the shader draws in the sprite's own
  // pass, there is no filter and so no extra render pass.
  const passes = '({ shaders: __gm.shaderCount(), filters: __gm.filterCount() })';
  const passesOn = await json(passes);
  await assetProps({ shader: '' });
  await sleep(300);
  const passesOff = await json(passes);
  await assetProps({ shader: ADJUST });
  await sleep(300);
  check(
    'a shaded sprite draws with its own shader and no filter pass – and plain without',
    passesOn.shaders === 1 && passesOn.filters === 0 && passesOff.shaders === 0 && passesOff.filters === 0,
    {
      on: passesOn,
      off: passesOff,
    },
  );
  await assetProps({ brightness: 1.25 });
  await sleep(300);
  const lighter = await centre();
  check('brightness 1.25 adds a quarter to every channel', colourDistance(lighter, '#80c0ff') < 24, lighter);
  await assetProps({ brightness: 1, contrast: 0 });
  await sleep(300);
  const flat = await centre();
  check('contrast 0 flattens the colour to mid grey', colourDistance(flat, '#808080') < 24, flat);
  await assetProps({ contrast: 1, saturation: 0 });
  await sleep(300);
  const grey = await centre();
  check('saturation 0 leaves the luma as a grey', colourDistance(grey, '#7c7c7c') < 24, grey);
  await shot('28-shader-desaturated');

  // 28f. The game draws through the same path, so play shows the shader too.
  await assetProps({ saturation: 1, brightness: 1.25 });
  await play();
  await sleep(500);
  const at = await json("__gm.gameScreen('oshade')");
  const played = at ? await json(`__gm.pixelAt(${Math.round(at.x + 20)}, ${Math.round(at.y + 20)})`) : null;
  check(
    'during play the sprite is drawn with its shader',
    played !== null && colourDistance(played, '#80c0ff') < 24,
    JSON.stringify({ at, played }),
  );
  await stop();
  await sleep(300);

  // 28g. Editing a shader's graph reaches every sprite wearing it: a Color wired into the new one's Output.
  await assetProps({ brightness: 1, shader: made.id });
  await sleep(300);
  const through = await centre();
  check(
    'the new shader passes the texel through',
    colourDistance(through, base) < 6,
    JSON.stringify({ base, through }),
  );
  await mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    const out = a.graph.nodes.find((n) => n.type === 'ShaderOutput');
    a.graph.nodes.push({ id: 'sh-red', type: 'ShaderColor', x: 0, y: 200, params: { value: 0xff0000 } });
    a.graph.edges.push({ id: 'sh-red-edge', from: { node: 'sh-red', port: 'color' }, to: { node: out.id, port: 'color' } });`);
  await sleep(400);
  const red = await centre();
  check(
    'wiring a red Color into the Output recompiles: the sprite turns red',
    colourDistance(red, '#ff0000') < 24,
    red,
  );

  // 28h. Alpha: Texture alpha times a Property into the Output's alpha blends the sprite with what
  // is behind it; at 1 the pixel is the one from before, byte for byte.
  await mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    const out = a.graph.nodes.find((n) => n.type === 'ShaderOutput');
    a.graph.nodes.push(
      { id: 'sh-alpha', type: 'ShaderTextureAlpha', x: 0, y: 300, params: {} },
      { id: 'sh-opacity', type: 'ShaderProperty', x: 0, y: 400, params: { name: 'opacity', default: 1, min: 0, max: 1 } },
      { id: 'sh-fade', type: 'ShaderMultiply', x: 200, y: 350, params: {} });
    a.graph.edges.push(
      { id: 'sh-fade-a', from: { node: 'sh-alpha', port: 'value' }, to: { node: 'sh-fade', port: 'a' } },
      { id: 'sh-fade-b', from: { node: 'sh-opacity', port: 'value' }, to: { node: 'sh-fade', port: 'b' } },
      { id: 'sh-fade-out', from: { node: 'sh-fade', port: 'result' }, to: { node: out.id, port: 'alpha' } });`);
  await sleep(400);
  const opaque = await centre();
  check(
    'an opacity property at its default 1 changes nothing',
    opaque === red,
    JSON.stringify({ red, opaque, info: await info() }),
  );
  await assetProps({ opacity: 0 });
  await sleep(300);
  const behind = await centre();
  check('opacity 0 shows what is behind the sprite', colourDistance(behind, red) > 60, { red, behind });
  await assetProps({ opacity: 0.5 });
  await sleep(300);
  const half = await centre();
  const channel = (hex, i) => parseInt(hex.slice(i, i + 2), 16);
  const expected =
    '#' +
    [1, 3, 5]
      .map((i) =>
        Math.round((channel(red, i) + channel(behind, i)) / 2)
          .toString(16)
          .padStart(2, '0'),
      )
      .join('');
  check('opacity 0.5 blends the sprite half with what is behind', colourDistance(half, expected) < 24, {
    red,
    behind,
    half,
    expected,
  });
  await assetProps({ opacity: 1 });
  await sleep(300);
  check('opacity back at 1 draws the pixel from before, byte for byte', (await centre()) === red);

  // 28i. A Number node is a constant in the fragment: red times 0.5 is half red; typed back to 1,
  // the pixel is the red from before. Its value is a setting row on the node.
  await mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    const out = a.graph.nodes.find((n) => n.type === 'ShaderOutput');
    a.graph.nodes.push(
      { id: 'sh-half', type: 'ShaderNumber', x: 200, y: 200, params: { value: 0.5 } },
      { id: 'sh-dim', type: 'ShaderMultiply', x: 400, y: 200, params: {} });
    a.graph.edges = a.graph.edges.filter((e) => e.id !== 'sh-red-edge');
    a.graph.edges.push(
      { id: 'sh-dim-a', from: { node: 'sh-red', port: 'color' }, to: { node: 'sh-dim', port: 'a' } },
      { id: 'sh-dim-b', from: { node: 'sh-half', port: 'value' }, to: { node: 'sh-dim', port: 'b' } },
      { id: 'sh-dim-out', from: { node: 'sh-dim', port: 'result' }, to: { node: out.id, port: 'color' } });`);
  await sleep(400);
  const dimmed = await centre();
  check('a Number of 0.5 into a Multiply halves the red', colourDistance(dimmed, '#800000') < 6, {
    red,
    dimmed,
  });
  await evaluate("__gm.showTab('shader')");
  await sleep(300);
  check(
    'the Number node draws its value as a setting row',
    (await json("__gm.shader.nodeSettings('sh-half')"))?.join() === 'Value: 0.500',
    JSON.stringify(await json("__gm.shader.nodeSettings('sh-half')")),
  );
  await shot('28-number-node');
  await evaluate("__gm.showTab('scene')");
  await mutate(`
    const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
    a.graph.nodes.find((n) => n.id === 'sh-half').params.value = 1`);
  await sleep(400);
  check('the Number typed to 1 gives the red from before, byte for byte', (await centre()) === red, {
    red,
    now: await centre(),
  });

  // 28k. UV into Step: the pixel's place on the picture decides its colour – a hard cut at u = 0.5,
  // then at v = 0.5, which shows v runs top to bottom. `box` is the sprite's centre and size.
  const node = (id, type, params = {}, x = 0, y = 0) => ({ id, type, x, y, params });
  const edge = (from, fromPort, to, toPort) => ({
    id: `${from}-${to}-${toPort}`,
    from: { node: from, port: fromPort },
    to: { node: to, port: toPort },
  });
  const graph = (nodes, edges) =>
    mutate(`
      const a = __gm.state.project.assets.find((x) => x.id === ${JSON.stringify(made.id)});
      a.graph.nodes = ${JSON.stringify(nodes)};
      a.graph.edges = ${JSON.stringify(edges)};`);
  const pixel = (fx, fy) =>
    json(`__gm.pixelAt(${Math.round(box.x + fx * box.w)}, ${Math.round(box.y + fy * box.h)})`);
  const redOrBlue = (t, edges) =>
    graph(
      [
        ...t,
        node('red', 'ShaderColor', { value: 0xff0000 }, 260, 200),
        node('blue', 'ShaderColor', { value: 0x0000ff }, 260, 340),
        node('mix', 'ShaderMix', {}, 520, 200),
        node('out', 'ShaderOutput', {}, 780, 200),
      ],
      [
        ...edges,
        edge('red', 'color', 'mix', 'a'),
        edge('blue', 'color', 'mix', 'b'),
        edge('mix', 'result', 'out', 'color'),
      ],
    );
  const cutAt = (port) =>
    redOrBlue(
      [node('uv', 'ShaderUV'), node('cut', 'ShaderStep', { edge: 0.5 }, 260, 0)],
      [edge('uv', port, 'cut', 'value'), edge('cut', 'result', 'mix', 't')],
    );
  await cutAt('u');
  await sleep(400);
  const uLeft = await pixel(-0.3, -0.3);
  const uRight = await pixel(0.3, -0.3);
  check(
    'UV into Step: left of u = 0.5 the sprite is red, right of it blue',
    colourDistance(uLeft, '#ff0000') < 6 && colourDistance(uRight, '#0000ff') < 6,
    { uLeft, uRight },
  );
  await cutAt('v');
  await sleep(400);
  const vTop = await pixel(-0.3, -0.3);
  const vBottom = await pixel(-0.3, 0.3);
  check(
    'v runs top to bottom: above v = 0.5 red, below it blue',
    colourDistance(vTop, '#ff0000') < 6 && colourDistance(vBottom, '#0000ff') < 6,
    { vTop, vBottom },
  );

  // 28k-ii. Pow bends the cut: u squared crosses 0.5 at u = 0.707, its square root at u = 0.25.
  const cutAfterPow = (exponent) =>
    redOrBlue(
      [
        node('uv', 'ShaderUV'),
        node('pow', 'ShaderPow', { exponent }, 260, 0),
        node('cut', 'ShaderStep', { edge: 0.5 }, 260, 120),
      ],
      [
        edge('uv', 'u', 'pow', 'value'),
        edge('pow', 'result', 'cut', 'value'),
        edge('cut', 'result', 'mix', 't'),
      ],
    );
  await cutAfterPow(2);
  await sleep(400);
  const squaredNear = await pixel(0.1, -0.3);
  const squaredFar = await pixel(0.3, -0.3);
  check(
    'Pow 2 moves the cut to u = 0.707: still red at u = 0.6, blue at 0.8',
    colourDistance(squaredNear, '#ff0000') < 6 && colourDistance(squaredFar, '#0000ff') < 6,
    { squaredNear, squaredFar },
  );
  await cutAfterPow(0.5);
  await sleep(400);
  const rootNear = await pixel(-0.3, -0.3);
  const rootFar = await pixel(-0.15, -0.3);
  check(
    'Pow 0.5 pulls it to u = 0.25: red at u = 0.2, blue at 0.35',
    colourDistance(rootNear, '#ff0000') < 6 && colourDistance(rootFar, '#0000ff') < 6,
    { rootNear, rootFar },
  );

  // 28k-iii. Abs folds u around 0.5 into a V: |u - 0.5| is below 0.25 only in the middle half.
  await redOrBlue(
    [
      node('uv', 'ShaderUV'),
      node('centred', 'ShaderSubtract', { b: 0.5 }, 260, 0),
      node('fold', 'ShaderAbs', {}, 260, 120),
      node('cut', 'ShaderStep', { edge: 0.25 }, 260, 240),
    ],
    [
      edge('uv', 'u', 'centred', 'a'),
      edge('centred', 'result', 'fold', 'value'),
      edge('fold', 'result', 'cut', 'value'),
      edge('cut', 'result', 'mix', 't'),
    ],
  );
  await sleep(400);
  const foldLeft = await pixel(-0.4, -0.3);
  const foldMiddle = await pixel(0, -0.3);
  const foldRight = await pixel(0.4, -0.3);
  check(
    'Abs folds the cut into a V: red in the middle, blue at both edges',
    colourDistance(foldMiddle, '#ff0000') < 6 &&
      colourDistance(foldLeft, '#0000ff') < 6 &&
      colourDistance(foldRight, '#0000ff') < 6,
    { foldLeft, foldMiddle, foldRight },
  );

  // 28l. Sample texture reads the picture where the graph says. On a pasted two-colour picture:
  // flipped u swaps the halves; u + 0.5 past the border shows the Output's Edge – Repeat continues
  // with the far half, Mirror with the near one.
  await evaluate(PASTE_HALVES);
  await sleep(2500);
  const picture = await json(FIND_HALVES);
  check(
    'a two-colour picture is pasted in for the sampling checks',
    Boolean(picture),
    JSON.stringify(picture),
  );
  await evaluate('__gm.state.select(null)');
  await assetProps({ texture: picture?.id ?? '', color: 0xffffff });
  await graph(
    [node('texel', 'ShaderTextureColor'), node('out', 'ShaderOutput')],
    [edge('texel', 'color', 'out', 'color')],
  );
  await sleep(600);
  const plainLeft = await pixel(-0.3, -0.3);
  const plainRight = await pixel(0.3, -0.3);
  check(
    'through Texture color the picture is on: red left, green right',
    colourDistance(plainLeft, LEFT) < 12 && colourDistance(plainRight, RIGHT) < 12,
    { plainLeft, plainRight },
  );
  const sampleAt = (uNodes, uEdges, outParams = {}) =>
    graph(
      [
        node('uv', 'ShaderUV'),
        ...uNodes,
        node('sample', 'ShaderSample', {}, 520, 0),
        node('out', 'ShaderOutput', outParams, 780, 0),
      ],
      [...uEdges, edge('sample', 'color', 'out', 'color')],
    );
  await sampleAt(
    [node('flip', 'ShaderSubtract', { a: 1 }, 260, 0)],
    [edge('uv', 'u', 'flip', 'b'), edge('flip', 'result', 'sample', 'u')],
  );
  await sleep(400);
  const flipLeft = await pixel(-0.3, -0.3);
  const flipRight = await pixel(0.3, -0.3);
  check(
    'sampling at 1 - u mirrors the picture: green left, red right',
    colourDistance(flipLeft, RIGHT) < 12 && colourDistance(flipRight, LEFT) < 12,
    { flipLeft, flipRight },
  );
  const scrolled = async (edgeMode) => {
    await sampleAt(
      [node('shift', 'ShaderAdd', { b: 0.5 }, 260, 0)],
      [edge('uv', 'u', 'shift', 'a'), edge('shift', 'result', 'sample', 'u')],
      { edge: edgeMode },
    );
    await sleep(400);
    return { left: await pixel(-0.3, -0.3), right: await pixel(0.3, -0.3) };
  };
  const repeat = await scrolled('repeat');
  check(
    'u + 0.5 with Edge Repeat: the near half shows the far one, and past the border the picture starts over',
    colourDistance(repeat.left, RIGHT) < 12 && colourDistance(repeat.right, LEFT) < 12,
    repeat,
  );
  const mirror = await scrolled('mirror');
  check(
    'the same with Edge Mirror: past the border the picture turns back on itself',
    colourDistance(mirror.left, RIGHT) < 12 && colourDistance(mirror.right, RIGHT) < 12,
    mirror,
  );
  // u + 0.5 cannot tell Clamp from Mirror: both hold green past the border. u + 0.8 puts the near
  // half on 1.6, where Mirror is already back in the far half and Clamp still holds the last texel.
  const scrolledFar = async (outParams) => {
    await sampleAt(
      [node('far', 'ShaderAdd', { b: 0.8 }, 260, 0)],
      [edge('uv', 'u', 'far', 'a'), edge('far', 'result', 'sample', 'u')],
      outParams,
    );
    await sleep(400);
    return pixel(0.3, -0.3);
  };
  const byDefault = await scrolledFar({});
  const byMirror = await scrolledFar({ edge: 'mirror' });
  check(
    'with nothing set on the Output the edge is Clamp: at u + 0.8 the border texel goes on, where Mirror shows the near half again',
    colourDistance(byDefault, RIGHT) < 12 && colourDistance(byMirror, LEFT) < 12,
    { byDefault, byMirror },
  );
  await evaluate("__gm.showTab('shader')");
  await sleep(300);
  await shot('28-shader-scroll-graph');
  await evaluate("__gm.showTab('scene')");
  await sleep(300);
  const sizeAtLeast = async (px) => {
    await redOrBlue(
      [node('size', 'ShaderTextureSize'), node('cut', 'ShaderStep', { edge: px }, 260, 0)],
      [edge('size', 'width', 'cut', 'value'), edge('cut', 'result', 'mix', 't')],
    );
    await sleep(400);
    return pixel(-0.3, -0.3);
  };
  const wide = await sizeAtLeast(31.5);
  const wider = await sizeAtLeast(32.5);
  check(
    'Texture size reads the picture’s pixel width: at least 31.5, not 32.5',
    colourDistance(wide, '#0000ff') < 6 && colourDistance(wider, '#ff0000') < 6,
    { wide, wider },
  );

  // 28m. Time: with the clock held the pixel is a function of the second; released, a sprite wearing
  // a Time shader redraws by itself in the scene view, where nothing else ticks, and in play.
  await redOrBlue(
    [
      node('time', 'ShaderTime'),
      node('saw', 'ShaderFract', {}, 260, 0),
      node('cut', 'ShaderStep', { edge: 0.5 }, 260, 120),
    ],
    [
      edge('time', 'value', 'saw', 'value'),
      edge('saw', 'result', 'cut', 'value'),
      edge('cut', 'result', 'mix', 't'),
    ],
  );
  await evaluate('__gm.shaderTime(0.2)');
  await sleep(400);
  const early = await pixel(-0.3, -0.3);
  await evaluate('__gm.shaderTime(0.7)');
  await sleep(400);
  const late = await pixel(-0.3, -0.3);
  check(
    'Time into Fract and Step: red at 0.2 s, blue at 0.7 s',
    colourDistance(early, '#ff0000') < 6 && colourDistance(late, '#0000ff') < 6,
    { early, late },
  );
  await redOrBlue(
    [node('time', 'ShaderTime'), node('saw', 'ShaderFract', {}, 260, 0)],
    [edge('time', 'value', 'saw', 'value'), edge('saw', 'result', 'mix', 't')],
  );
  await evaluate('__gm.shaderTime(null)');
  await sleep(400);
  const first = await pixel(-0.3, -0.3);
  await sleep(400);
  const second = await pixel(-0.3, -0.3);
  const animates = await json('__gm.animates()');
  check(
    'released, the scene view redraws every tick for the Time shader: the colour moves with nothing running',
    animates.scene === true && animates.game === false && first !== second,
    { animates, first, second },
  );
  // (#90) The shader clock is the global one: a scale of 0 holds the colour where it is without
  // freezing anything shader-specific, and 1 lets it move on.
  await evaluate('__gm.setTimeScale(0)');
  await sleep(400);
  const frozenEarly = await pixel(-0.3, -0.3);
  await sleep(400);
  const frozenLate = await pixel(-0.3, -0.3);
  await evaluate('__gm.setTimeScale(1)');
  await sleep(400);
  const thawed = await pixel(-0.3, -0.3);
  check(
    'a global time scale of 0 stops the shader clock, and 1 starts it again',
    frozenEarly === frozenLate && thawed !== frozenLate,
    { frozenEarly, frozenLate, thawed },
  );
  await play();
  await sleep(500);
  const playing = await json('__gm.animates()');
  await stop();
  await sleep(300);
  check('and so does the game view while playing', playing.game === true, JSON.stringify(playing));
  await assetProps({ shader: '' });
  await sleep(400);
  check(
    'with the shader off the scene view stops redrawing',
    (await json('__gm.animates()')).scene === false,
    JSON.stringify(await json('__gm.animates()')),
  );
  await assetProps({ texture: '', color: 0x4080ff, shader: made.id });
  await sleep(400);

  // 28j. Back to None: no filter at all, the plain colour returns bit for bit.
  await assetProps({ shader: '' });
  await sleep(300);
  const back = await centre();
  check(
    'switching back to None restores the plain colour',
    colourDistance(back, base) < 6,
    JSON.stringify({ base, back }),
  );

  await mutate(`
    const project = __gm.state.project;
    const gone = new Set(['shade-sprite', ${JSON.stringify(made.id)}, ${JSON.stringify(picture?.id ?? '')}]);
    project.assets = project.assets.filter((a) => !gone.has(a.id));
    const scene = __gm.state.activeScene;
    scene.objects = scene.objects.filter((o) => o.id !== 'oshade')`);
  await evaluate('__gm.state.select(null)');
  await sleep(200);
  check(
    'the step leaves nothing behind but the fixture’s shader',
    (await json("__gm.state.project.assets.some((a) => a.id === 'shade-sprite')")) === false &&
      (await json("__gm.state.activeScene.objects.some((o) => o.id === 'oshade')")) === false &&
      (await json(`__gm.state.project.assets.some((a) => a.id === ${JSON.stringify(picture?.id ?? '')})`)) ===
        false &&
      (await shaders()).map((s) => s.id).join(',') === ADJUST,
  );
}