spiral

void setup() {
  size(800, 800);
  background(255);
  float sw=0;
  float theta = 0;
  int centX = width/2;
  int centY = height/2;

  stroke(20, 50, 70);
  float radius = 5;
  float x, y;
  float lastx = -999;
  float lasty = -999;
  for (float ang = 0; ang <= 8*360; ang += 4) {
    sw = map(sin(theta*1.5), -1, 1, 4, 40);
    strokeWeight(sw);
    radius += 0.8;
    float rad = radians(ang);
    x = centX + (radius * cos(rad));
    y = centY + (radius * sin(rad));
    if (lastx > -999) {
      line(x, y, lastx, lasty);
    }
    lastx = x;
    lasty = y;
    theta += 0.05;
  }
}