This example is for Processing 3+. If you have a previous version, use the examples included with your software. If you see any errors or have suggestions, please let us know.

Setup and Draw.

The code inside the draw() function runs continuously from top to bottom until the program is stopped. The code in setup() is run once when the program starts.

int y = 180;

// The statements in the setup() block run once 
// when the program begins
void setup() {
  size(640, 360);  // Size must be the first statement
  stroke(255);  // Set line drawing color to white

// The statements in draw() are run until the program 
// is stopped. Each statement is run in sequence from top 
// to bottom and after the last line is read, the 
// first line is run again.
void draw() { 
  background(0);  // Clear the screen with a black background
  line(0, y, width, y); 
  y = y - 1; 
  if (y < 0) { 
    y = height;