Crevasse Field

// composition: a crevasse field — ice strata run as long diagonal bands upper-left to lower-right; dark stepped cracks concentrate center-right; upper-left stays clean ice
// layering: pale diagonal strata, quiet snow shelf, blue crevasse walls and their lit lips, snow-grain, one warm rock shoulder.
const PALETTE = [
  "#eef3f4", // paper / clean ice
  "#c7dfe6", // pale cyan strata
  "#b5d3dc", // deeper ice band
  "#17434c", // crevasse shadow teal
  "#a8713f", // warm rock exposure — the single accent
];

// Each fissure has a sunward lip, a blue wall and a narrow, tapering throat.
// The width belongs to the pressure field, rather than to the drawing pen.
const iceFissure = (pts, breadth) => {
  const rim = pts.map(([x, y], i) => {
    const t = i / (pts.length - 1);
    const opening = breadth * Math.pow(Math.sin(Math.PI * t), 0.7);
    return [x + opening, y + opening * 0.43];
  });
  brush.noStroke();
  brush.fillBleed(0.3, "out");
  brush.fillTexture(0.55, 0.46);
  brush.fill(PALETTE[2], 170);
  brush.polygon([...pts, ...rim.slice().reverse()]);
  for (let i = 0; i < pts.length - 1; i++) {
    const a = pts[i], b = pts[i + 1], c = rim[i + 1], d = rim[i];
    brush.noStroke();
    brush.fillBleed(0.22, "out");
    brush.fill(PALETTE[3], 150);
    brush.polygon([a, b, [lerp(b[0], c[0], 0.38), lerp(b[1], c[1], 0.38)],
      [lerp(a[0], d[0], 0.38), lerp(a[1], d[1], 0.38)]]);
    brush.noFill();
    brush.set("cpencil", PALETTE[3], 0.65 + breadth * 0.023);
    brush.line(a[0], a[1], b[0], b[1]);
    if (i > 0 && i < pts.length - 2) {
      brush.set("2H", "#7fa9b6", 0.65);
      for (let j = 1; j < 5; j++) {
        const t = j / 5;
        brush.line(lerp(a[0], b[0], t) + 3, lerp(a[1], b[1], t) + 2,
          lerp(d[0], c[0], t), lerp(d[1], c[1], t));
      }
      brush.set("cpencil", PALETTE[0], 1.8);
      brush.line(d[0] + 2, d[1] - 2, c[0] + 2, c[1] - 2);
    }
  }
};

function setup() {
  createCanvas(800, 800, WEBGL);
  angleMode(DEGREES);
  brush.scaleBrushes(2.4);
  noLoop();
}

function draw() {
  translate(-width / 2, -height / 2);
  background("#eef3f4");

  // a quiet ice-blue tint over the whole sheet — no bare paper anywhere
  brush.noStroke();
  brush.fillBleed(0.4, "out");
  brush.fillTexture(0.35, 0.3);
  brush.fill("#ddedf0", 55);
  brush.rect(-30, -30, 860, 860);

  // strata — long parallel band washes in a rotated frame
  push();
  translate(400, 400);
  rotate(38);
  const bandCols = ["#c7dfe6", "#b5d3dc", "#ddedf0"];
  for (let i = 0; i < 19; i++) {
    const d = -500 + i * 55 + randomGaussian(0, 6);
    const w = random(22, 56);
    const op = constrain(78 + randomGaussian(0, 20) + i * 2.4, 50, 160);
    brush.noStroke();
    brush.fillBleed(0.3, "out");
    brush.fillTexture(0.45, 0.4);
    brush.fill(bandCols[i % 3], op);
    brush.beginShape(0.35);
    brush.vertex(-720, d + randomGaussian(0, 5));
    brush.vertex(-260, d - w * 0.4 + randomGaussian(0, 8));
    brush.vertex(230, d + randomGaussian(0, 8));
    brush.vertex(720, d - randomGaussian(0, 6));
    brush.vertex(720, d + w);
    brush.vertex(10, d + w + randomGaussian(0, 9));
    brush.vertex(-720, d + w * 0.9);
    brush.endShape(true);
  }
  // a few thin strata edge lines
  brush.set("2H", "#7fa9b6", 0.85);
  for (let i = 0; i < 6; i++) {
    const d = random(-420, 460);
    brush.line(-650, d, 650, d + randomGaussian(0, 10));
  }
  pop();

  // clean-ice veil — quiet the upper-left to pale ice-blue, not bare paper
  brush.noStroke();
  brush.fillBleed(0.5, "out");
  brush.fillTexture(0.35, 0.3);
  brush.fill("#dcebef", 95);
  brush.polygon([[-30, -30], [470, -30], [220, 250], [-30, 480]]);
  brush.fill("#e6f1f3", 70);
  brush.polygon([[-30, -30], [360, -30], [130, 190], [-30, 340]]);

  // The large openings diverge without crossing; the left snow shelf stays quiet.
  iceFissure([[538, 154], [510, 205], [472, 252], [489, 271], [441, 329],
    [398, 382], [416, 400], [367, 469], [323, 527], [292, 572]], 38);
  iceFissure([[656, 220], [627, 263], [584, 317], [598, 336], [552, 389],
    [522, 437], [537, 453], [490, 516], [458, 575], [427, 620]], 27);
  iceFissure([[742, 367], [713, 408], [676, 454], [689, 471], [647, 524],
    [610, 580], [622, 598], [582, 650], [554, 686]], 20);
  iceFissure([[440, 330], [400, 319], [365, 285], [340, 278]], 8);
  iceFissure([[522, 436], [491, 415], [469, 387]], 6);

  // snow-grain — spray drifting over the lower and right ice
  brush.set("spray", "#f4f8f8", 3.2);
  for (let i = 0; i < 9; i++) {
    const sx = random(300, 720);
    const sy = random(380, 740);
    brush.line(sx, sy, sx + random(50, 130), sy + random(30, 90));
  }
  brush.set("spray", "#cfe4ea", 2.6);
  for (let i = 0; i < 5; i++) {
    const sx = random(120, 420);
    const sy = random(480, 730);
    brush.line(sx, sy, sx + random(40, 100), sy + random(20, 70));
  }

  // one warm rock exposure, shouldering out of a crevasse wall
  brush.noStroke();
  brush.fillBleed(0.3, "out");
  brush.fillTexture(0.6, 0.7);
  brush.fill("#a8713f", 150);
  brush.polygon([[544, 425], [558, 413], [575, 428], [566, 450], [538, 454]]);
  brush.fill("#8a5a30", 120);
  brush.polygon([[541, 444], [558, 434], [568, 430], [561, 450], [538, 454]]);
  brush.noFill();
  brush.set("2B", "#635647", 1.2);
  brush.line(539, 453, 561, 450);
  brush.line(561, 450, 570, 432);
  brush.set("2H", PALETTE[0], 0.9);
  brush.line(546, 424, 558, 416);
}