/**
 * No Loop. 
 * 
 * The noLoop() function causes draw() to only
 * execute once. Without calling noLoop(), the 
 * code inside draw() is run continually. 
 */

float y;

// The statements in the setup() function 
// execute once when the program begins
void setup() 
{
  size(640, 360);  // Size should be the first statement
  stroke(255);     // Set line drawing color to white
  noLoop();
  
  y = height * 0.5;
}

// 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; 
  if (y < 0) { y = height; } 
  line(0, y, width, y);  
}