Procion: Variation on a theme by Victor Vasarely

int N=4; float t, h; 

void setup() 
{
  size(600,600); frameRate(30);ellipseMode(CORNER);
  smooth();  noStroke(); colorMode(HSB,360,100,100); 
  t=0; h=0;
}

void draw() 
{
  t+=1/30.0; h=(h+0.1)%360;
  background(0);
  int i, j, w=width/N; 
  float f=0.05;
  for(i=0;i<N*N;i++){
    fill(h,80,80);
    ellipse((f+i%N)*w,(f+int(i/N))*w,w*(1-2*f),w*(1-2*f));
    fill(0,0,0);
    rect((1/3.0+i%N)*w, (1/3.0+int(i/N))*w, w/3.0, w/3.0);
  }
   for(i=0;i<N*(N-1);i++){
    rect((5/6.0+i%(N-1)+1/6.0*cos(0.3*t+(i%2)*PI))*w, 
         (1/3.0+int(i/(N-1)))*w, w/3.0, w/3.0);
    rect((1/3.0+i%N)*w, (5/6.0+int(i/N)
          +1/6.0*cos(0.3*t+((i+int(i/N))%2)*PI))*w,
          w/3.0, w/3.0);
  } 
}