void setup()
{size(400,400);
background(255);
noStroke();
}
float y=0;
void draw()
{
for(int i=0; i<sq(height); i+=sq(height/5))
{
  
  fill(255*i/sq(height));
  rect((mouseX-width/2)*sqrt(i)/width+sqrt(i)/2,(mouseY-height/2)*sqrt(i)/height+sqrt(i)/2,width-sqrt(i),height-sqrt(i));
  }
  }