Lightning in Processing

int startX, startY, endX, endY;

void setup(){
  size(640,480);
  startX = 0;
  startY = 150;
}

void draw(){
  stroke((int)(Math.random()*256),(int)(Math.random()*256),(int)(Math.random()*256));
  endX = startX + (int)(Math.random() * 9 + 1);
  endY = startY + (int)(Math.random() * 19 - 9);
  line(startX, startY, endX, endY);
  startX = endX;
  startY = endY;
  startX %= width;
  startY %= height;
}