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.

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
  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);