void setup() {
  size(200, 200);
  noLoop();
  background(51);
  stroke (random(255),random(255),random(255));
}

float x = 0;

void draw() {
  x += .1;
  if (x > width) {
    x = 0;
    stroke (random(255),random(255),random(255));
  }
  line(x, 0, x, height); 
}

void mousePressed() {
  stroke (random(255),random(255),random(255));
  loop();
}

void mouseReleased() {
  stroke (random(255),random(255),random(255));
  noLoop();
}