Function generateImageCaptcha

pmcaptcha/pmcaptcha.ts:557–655

(
  digitOnly: boolean
)

  const CHARSET_MIXED = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";

  const charset = digitOnly ? CHARSET_DIGIT : CHARSET_MIXED;
  const LENGTH  = 5;

  let answer = "";
  for (let i = 0; i < LENGTH; i++) {
    answer += charset[Math.floor(Math.random() * charset.length)];
  }

  const W = 240, H = 90;
  const canvas = cv.createCanvas(W, H);
  const ctx    = canvas.getContext("2d") as CanvasRenderingContext2D;

  const rnd  = () => Math.random();
  const rndI = (min: number, max: number) => Math.floor(rnd() * (max - min + 1)) + min;

  for (let i = 0; i < 12; i++) {
    ctx.fillStyle = `hsla(${rndI(0,360)},30%,${rndI(85,97)}%,0.9)`;
    ctx.fillRect(rndI(0, W), rndI(0, H), rndI(20, 80), rndI(20, 60));
  }

  ctx.strokeStyle = `rgba(180,180,200,0.35)`;
  ctx.lineWidth = 0.8;
  for (let x = 0; x < W; x += rndI(18, 28)) {
    ctx.beginPath(); ctx.moveTo(x, 0); ctx.lineTo(x, H); ctx.stroke();
  }
  for (let y = 0; y < H; y += rndI(18, 28)) {
    ctx.beginPath(); ctx.moveTo(0, y); ctx.lineTo(W, y); ctx.stroke();
  }

  for (let i = 0; i < 8; i++) {
    ctx.beginPath();
    ctx.moveTo(0, rnd() * H);
    ctx.bezierCurveTo(W * 0.25, rnd() * H, W * 0.75, rnd() * H, W, rnd() * H);
    ctx.strokeStyle = `hsla(${rndI(0,360)},55%,45%,${0.3 + rnd() * 0.3})`;
    ctx.lineWidth   = 1 + rnd();
    ctx.stroke();
  }

  for (let i = 0; i < 180; i++) {
    ctx.beginPath();
    ctx.arc(rnd() * W, rnd() * H, 0.8 + rnd() * 1.5, 0, Math.PI * 2);
    ctx.fillStyle = `hsla(${rndI(0,360)},50%,35%,${0.4 + rnd() * 0.4})`;
    ctx.fill();
  }

  for (let i = 0; i < 8; i++) {
    ctx.fillStyle = `hsla(${rndI(0,360)},60%,60%,0.15)`;
    ctx.fillRect(rnd() * W, rnd() * H, rndI(8, 30), rndI(4, 16));
  }

  const STEP = (W - 24) / LENGTH;
  for (let i = 0; i < LENGTH; i++) {
    const ch  = answer[i];
    const x   = 14 + i * STEP + STEP * 0.35;
    const y   = H / 2 + (rnd() - 0.5) * 18;
    const rot = (rnd() - 0.5) * 0.65;
    const sz  = 32 + rndI(0, 10);