Dusk Falling

// Four unequal curtains of dusk: the plum field holds the left, amber thins at the right.
// Stained strips under dry vertical grain; torn shoulders and a single warm seam. Margins stay open.
const PALETTE = ["#f1e8dc", "#5e3a56", "#8f6280", "#c68a86", "#d9a05b"];
const BANDS = [[96, 320, 152, 664, 1], [320, 426, 172, 650, 2],
  [426, 570, 144, 672, 3], [570, 708, 186, 636, 4]];
const duskStrip = (x, y0, y1, w, col, opacity) => {
  brush.noStroke();
  brush.fillBleed(0.38, "out");
  brush.fillTexture(0.66, 0.5);
  brush.fill(col, opacity);
  brush.beginShape(0.15);
  brush.vertex(x, y0);
  brush.vertex(x + w, y0 + randomGaussian(0, 7));
  brush.vertex(x + w + randomGaussian(0, 2), y1);
  brush.vertex(x, y1 + randomGaussian(0, 8));
  brush.endShape(true);
};
function setup() {
  createCanvas(800, 800, WEBGL);
  brush.scaleBrushes(2.4);
  noLoop();
}
function draw() {
  translate(-width / 2, -height / 2);
  background(PALETTE[0]);
  for (const [left, right, top, bottom, index] of BANDS) {
    // Small overlapping deposits hold more pigment than one diluted rectangle.
    for (let i = 0; i < 11; i++) {
      const x = left + (right - left) * i / 11;
      const w = (right - left) / 11 + 5;
      const y0 = top + randomGaussian(0, 9);
      const y1 = bottom + randomGaussian(0, 10);
      duskStrip(x, y0, y1, w, PALETTE[index], 160);
      duskStrip(x + 2, y0 + 28, y1 - 12, w * 0.78, PALETTE[index], 134);
    }
    brush.noFill();
    for (let i = 0; i < 52; i++) {
      const x = constrain(randomGaussian((left + right) / 2, (right - left) * 0.35), left, right);
      const y = constrain(randomGaussian(400, 140), top + 8, bottom - 40);
      const len = constrain(randomGaussian(100, 38), 24, bottom - y);
      const col = lerpColor(color(PALETTE[index]), color(PALETTE[0]), constrain(randomGaussian(0.25, 0.18), 0, 0.75));
      brush.set(i % 5 === 0 ? "2B" : "cpencil", col, constrain(randomGaussian(1.5, 0.4), 0.7, 2.5));
      brush.beginShape(0.25);
      brush.vertex(x, y, 0.25);
      brush.vertex(x + randomGaussian(0, 1.2), y + len * 0.45, 1);
      brush.vertex(x + randomGaussian(0, 1.5), y + len, 0.2);
      brush.endShape(false);
    }
  }
  // Boundaries breathe instead of becoming four ruled columns.
  duskStrip(308, 286, 608, 14, PALETTE[2], 100);
  duskStrip(420, 208, 530, 10, PALETTE[3], 115);
  duskStrip(560, 346, 620, 13, PALETTE[2], 86);
  brush.noFill();
  brush.set("cpencil", PALETTE[4], 2.3);
  brush.beginShape(0.3);
  brush.vertex(214, 338, 0.2);
  brush.vertex(216, 412, 0.9);
  brush.vertex(213, 482, 0.3);
  brush.endShape(false);
}