Simple Function

void setup(){

  size(400,400);

  background(100);

  noStroke();

}

​

void draw(){

  target(100,100);

  target(300,300);

  target(100,300);

  target(300,100);

  target(350,200);

  target(50,200);

  target(200,50);

  target(200,350);

  target(200,200);

}

void target(int  x, int y){

  fill(255,0,0);

  ellipse(x,y,200,200);

  fill(255);

  ellipse(x,y,190,190);

  fill(255,0,0);

  ellipse(x,y,180,180);

   fill(255);

  ellipse(x,y,170,170);

  fill(255,0,0);

  ellipse(x,y,160,160);

   fill(255);

  ellipse(x,y,150,150);

  fill(255,0,0);

  ellipse(x,y,140,140);

}