Circles in Circles moving to give the illusion of spirals (processing v3)

perfect_spiral.pde

// inspired by https://gist.github.com/volfegan/e55decad6814e63fb450379c9bf13a61
// attempt to recreate: https://twitter.com/Borrachas/status/1204855395006763009

float a=0, b=0, x,y;
float shrink, spin_speed;

void setup() {
  size(800,800);
  shrink = 0.900;
  spin_speed = 0.1;
}

void draw() {
  float d;
  background(#FF0405);  
  translate(400,400);
  for (float diameter=1600; diameter > 1; diameter*=shrink) {
    d = norm(diameter, 0, 1600);

    strokeWeight(d * 25);
    fill(0,(1-d)*20);
    float inner_radius = d*100*shrink;
    x = cos((b*d*100*(1-shrink))+a) * inner_radius;
    y = sin((d*b*100*(1-shrink))+a) * inner_radius;
    
    circle(x,y, diameter);
    b += d;
  }
  b = 0;
  a += spin_speed;
}