void setup() 
{
  size(200, 200);  // Size should be the first statement
  stroke(255);     // Set line drawing color to white
  noLoop();
}

float y = 100;
float x = 50;

// The statements in draw() are executed until the 
// program is stopped. Each statement is executed in 
// sequence and after the last line is read, the first 
// line is executed again.
void draw() 
{ 
  background(0);   // Set the background to black
  y = y - 1; 
  x = x - 1; 
    if (y < 0) { y = height; } 
  line(0, y, width, y);  
    if (x < 0) { x = height; } 
  line(x, 0, width, x);  
  } 

void mousePressed() 
{
  loop();
}