This reference is for Processing 2.0+. If you have a previous version, use the reference included with your software. If you see any errors or have suggestions, please let us know. If you prefer a more technical reference, visit the Processing Javadoc.



float yPos = 0.0;

void setup() {  // setup() runs once
  size(200, 200);
void draw() {  // draw() loops forever, until stopped
  yPos = yPos - 1.0;
  if (yPos < 0) {
    yPos = height;
  line(0, yPos, width, yPos);

void setup() {
  size(200, 200);

// Although empty here, draw() is needed so
// the sketch can process user input events
// (mouse presses in this case).
void draw() { }

void mousePressed() {
  line(mouseX, 10, mouseX, 90);
Description Called directly after setup(), the draw() function continuously executes the lines of code contained inside its block until the program is stopped or noLoop() is called. draw() is called automatically and should never be called explicitly.

It should always be controlled with noLoop(), redraw() and loop(). If noLoop() is used to stop the code in draw() from executing, then redraw() will cause the code inside draw() to be executed a single time, and loop() will cause the code inside draw() to resume executing continuously.

The number of times draw() executes in each second may be controlled with the frameRate() function.

It is common to call background() near the beginning of the draw() loop to clear the contents of the window, as shown in the first example above. Since pixels drawn to the window are cumulative, omitting background() may result in unintended results, especially when drawing anti-aliased shapes or text.

There can only be one draw() function for each sketch, and draw() must exist if you want the code to run continuously, or to process events such as mousePressed(). Sometimes, you might have an empty call to draw() in your program, as shown in the second example above.
Updated on July 17, 2014 04:33:28am EDT

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