Gone to Seed

// composition: one dry thistle; the stem climbs from the bottom-left third to a crosshatched head at the left thirds crossing
// layering: ground ticks, doubled pen stem and spiky leaves, straw underwash, crosshatched involucre, radiating rotring spines, one violet wash crown last
const PALETTE = [
  "#f0e9d6", // straw paper
  "#c4ad74", // faded straw
  "#8a7146", // sepia
  "#4f4130", // dark sepia ink
  "#7a5c9e", // violet, the only color
];

const HX = 272; // head centre
const HY = 292;

function chord(psi, q, ax, ay, jit) {
  const h = Math.sqrt(Math.max(0, 1 - q * q)) * 0.96;
  const nx = Math.cos(psi + Math.PI / 2);
  const ny = Math.sin(psi + Math.PI / 2);
  const tx = Math.cos(psi);
  const ty = Math.sin(psi);
  brush.line(
    HX + ax * (q * nx - h * tx) + random(-jit, jit),
    HY + ay * (q * ny - h * ty) + random(-jit, jit),
    HX + ax * (q * nx + h * tx) + random(-jit, jit),
    HY + ay * (q * ny + h * ty) + random(-jit, jit)
  );
}

function setup() {
  createCanvas(800, 800, WEBGL);
  brush.scaleBrushes(2.3);
  noLoop();
}

function draw() {
  translate(-width / 2, -height / 2);
  background("#f0e9d6");

  // ground: a few dry ticks where the stem leaves the soil
  brush.set("2H", "#c4ad74", 0.8);
  brush.line(196, 786, 214, 776);
  brush.line(262, 790, 276, 780);
  brush.line(232, 796, 240, 782);
  brush.line(304, 788, 296, 776);
  brush.line(174, 794, 186, 788);

  // the stem, doubled like a dry hollow stalk
  brush.noFill();
  brush.set("pen", "#4f4130", 1.05);
  brush.beginShape(0.35);
  brush.vertex(238 + random(-2, 2), 800);
  brush.vertex(252 + random(-2, 2), 688);
  brush.vertex(258 + random(-2, 2), 566);
  brush.vertex(252 + random(-2, 2), 452);
  brush.vertex(264 + random(-2, 2), 360);
  brush.vertex(HX, HY + 40);
  brush.endShape(false);
  brush.set("pen", "#8a7146", 0.7);
  brush.beginShape(0.35);
  brush.vertex(245, 800);
  brush.vertex(257, 690);
  brush.vertex(263, 566);
  brush.vertex(257, 450);
  brush.vertex(268, 362);
  brush.endShape(false);

  // spiky dry leaves, drawn as jagged single lines
  brush.set("pen", "#4f4130", 0.9);
  brush.beginShape(0.15);
  brush.vertex(253, 664);
  brush.vertex(215, 650);
  brush.vertex(227, 671);
  brush.vertex(186, 663);
  brush.vertex(199, 686);
  brush.vertex(160, 683);
  brush.endShape(false);
  brush.beginShape(0.15);
  brush.vertex(256, 556);
  brush.vertex(292, 540);
  brush.vertex(281, 561);
  brush.vertex(318, 552);
  brush.vertex(306, 574);
  brush.endShape(false);
  brush.set("pen", "#8a7146", 0.8);
  brush.beginShape(0.15);
  brush.vertex(249, 734);
  brush.vertex(221, 744);
  brush.vertex(233, 756);
  brush.vertex(207, 764);
  brush.endShape(false);

  // one faint straw wash under the largest leaf
  brush.noStroke();
  brush.fillBleed(0.4, "out");
  brush.fillTexture(0.5, 0.5);
  brush.fill("#c4ad74", 42);
  brush.beginShape(0.5);
  brush.vertex(250, 660);
  brush.vertex(190, 656);
  brush.vertex(168, 682);
  brush.vertex(236, 676);
  brush.endShape(true);

  // involucre: a faint wash, then two passes of crosshatch chords
  brush.fill("#c4ad74", 55);
  brush.beginShape(0.6);
  brush.vertex(HX - 30, HY - 26);
  brush.vertex(HX + 30, HY - 28);
  brush.vertex(HX + 34, HY + 22);
  brush.vertex(HX, HY + 46);
  brush.vertex(HX - 33, HY + 20);
  brush.endShape(true);
  brush.set("rotring", "#8a7146", 0.6);
  for (let q = -0.88; q <= 0.9; q += 0.17) chord(0.62, q, 35, 45, 1.6);
  brush.set("rotring", "#4f4130", 0.55);
  for (let q = -0.82; q <= 0.86; q += 0.21) chord(2.25, q, 35, 45, 1.6);

  // bracts hooking down and out around the cup
  brush.set("pen", "#4f4130", 0.7);
  for (let i = 0; i < 16; i++) {
    const a = Math.PI * (0.12 + 0.76 * (i / 15));
    const bx = HX + Math.cos(a) * 33;
    const by = HY + 8 + Math.sin(a) * 40;
    const L = 14 + random(-4, 8);
    brush.line(bx, by, bx + Math.cos(a + 0.25) * L, by + Math.sin(a + 0.25) * L);
  }

  // the burst: fine spines radiating from the head, mostly straw, a few violet
  for (let i = 0; i < 56; i++) {
    const a = -Math.PI / 2 + randomGaussian(0, 0.6);
    const L = Math.max(26, randomGaussian(86, 24));
    const r = random();
    const col = r < 0.13 ? "#7a5c9e" : r < 0.58 ? "#c4ad74" : "#8a7146";
    brush.set("rotring", col, random(0.45, 0.75));
    const x0 = HX + Math.cos(a) * 14 + random(-4, 4);
    const y0 = HY - 34 + Math.sin(a) * 10;
    const mx = x0 + Math.cos(a) * L * 0.55;
    const my = y0 + Math.sin(a) * L * 0.55;
    const bend = random(-0.16, 0.16);
    brush.beginShape(0.3);
    brush.vertex(x0, y0);
    brush.vertex(mx, my);
    brush.vertex(mx + Math.cos(a + bend) * L * 0.45, my + Math.sin(a + bend) * L * 0.45);
    brush.endShape(false);
  }

  // the violet crown, three pooled washes
  brush.noStroke();
  brush.fillBleed(0.55, "out");
  brush.fillTexture(0.6, 0.6);
  brush.fill("#7a5c9e", 62);
  brush.circle(HX - 2 + random(-3, 3), HY - 62, 30, true);
  brush.fill("#7a5c9e", 108);
  brush.circle(HX + 3, HY - 68, 21, true);
  brush.fill("#7a5c9e", 168);
  brush.circle(HX - 1, HY - 58, 13, true);

  // one spine got away
  brush.set("rotring", "#8a7146", 0.5);
  brush.line(356, 214, 386, 196);
  brush.noStroke();
  brush.fill("#7a5c9e", 120);
  brush.circle(390, 192, 3.5, true);
}