Lab 8

This lab asks you to modify existing code. This code comes from the Learning Processing book by Daniel Shiffman (who also wrote a lot of the content on processing.org). He coded a solar system demonstration. This is what it looks like (obviously, the real program has moving planets):

Daniel Shiffman's solar system

We want to modify his code to produce something that looks like this (this image is scaled down):

My solar system

First, you'll want to create a new project and copy-paste the code below. Make sure you create a new "tab" for the Planet class when you paste that code. Next, create a data folder in your sketch folder and copy the planet images from planets.zip into the data folder. These images come from Open Clipart.

You'll also want to look at these planet tables for data about the size of each planet, how far it is from the sun, and how fast is its orbit.

Here is what you have to do:

Hint: you might want to add imageMode(CENTER); to the top of the setup() function so when you draw your images with image(0, 0, w, h) they will draw with the center of the image on 0,0. It makes everything easier.

Extra credit (+20pts): Draw a bunch of tiny stars. (Why not?) They should be randomly distributed, but they shouldn't move. You'll probably want to create a class called Star that has x and y variables which are set randomly in the constructor. This way, you can create an array of stars in setup(), then draw them in draw(); since each star keeps track of its own x and y, they won't move.

Extra credit (+30pts): Draw each planet rotated around its own axis for its day-night cycle (it doesn't matter how fast it rotates). This can be accomplished with the use of rotate() in the display() function of the class.

Extra credit (+50pts): Draw the moon rotating around Earth, and maybe some of Jupiter's moons, too. Use any one of the moon images provided. This is easier than you might think. Just modify the Planet class (maybe it should now be called Satellite) so that the constructor has another parameter: an array of planets or satellites which orbit this planet. For planets with no moons, just put null as the argument. For planets with moons, create another array (just like the planets array) and give that array to the planet constructor with the moons. Then, finally, before the planet display() function is finished, use a for() loop that tells each of the planet's moons (if the array is not null) to update() and display(). It's really that simple. You can even have moons with their own moons! Etc.

Main file

// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Example 14-18: Object-oriented solar system

// An array of 8 planet objects
Planet[] planets = new Planet[8];

void setup() {
  // The planet objects are initialized using the counter variable
  for (int i = 0; i < planets.length; i++ ) {
    planets[i] = new Planet(20 + i*10,i + 8);

void draw() {
  // Drawing the Sun
  // Drawing all Planets
  for (int i = 0; i < planets.length; i++ ) {

Planet class

// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Example 14-18: Object-oriented solar system

class Planet {
  // Each planet object keeps track of its own angle of rotation.
  float theta;      // Rotation around sun
  float diameter;   // Size of planet
  float distance;   // Distance from sun
  float orbitspeed; // Orbit speed
  Planet(float distance_, float diameter_) {
    distance = distance_;
    diameter = diameter_;
    theta = 0;
    orbitspeed = random(0.01,0.03);
  void update() {
    // Increment the angle to rotate
    theta += orbitspeed;
  void display() {
    // Before rotation and translation, the state of the matrix is saved with pushMatrix().
    // Rotate orbit
    // translate out distance
    // Once the planet is drawn, the matrix is restored with popMatrix() so that the next planet is not affected.

Some tips

CSE 1211 material by Joshua Eckroth is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. Source code for this website available at GitHub.