float x;
float vx;
void setup() {
  size(500, 500);
  x = 0;
  vx = 1;
}


void draw() {
  
  for (int i = 0; i < 10; i++) {
   // stroke(i*25, i*25, 0);
    stroke(0, 0, i*25);
    fill(255, 0, 0);
    rect(x, i*50, 20, sin(radians(x*3))*30);    
  }
  x = x+ vx;
  if (x < 0 || x > 500) {
    vx = -vx;
  }
}