void setup() {
  size(255,255);
  background(0);
}
void draw() {
  background(0);

  // While i is less than the width of the window
  for (int i = 0; i < width; i+=10) {
    noStroke();
    float distance = abs(mouseX–i);
    fill(distance);
    rect(i,0,10,height);
  }
}