void setup() {
  size(400,400);
  
}

void draw() {
  background(200);
  line(200,200, mouseX,mouseY);
  line(0,0, mouseX,mouseY);
  line(width,0, mouseX,mouseY);
  line(0,height, mouseX,mouseY);
  line(width,height, mouseX,mouseY);
}