Universe Maker | Planetary simulation game

Universe Maker is an n-body simulation of a planetary system on an Android app, written in Java. Get the app here!

Features

• Complete n-body simulation using an Euler integration physics solver.
• Objects coalesce upon colliding, and collisions are inelastic.
• A variety of celestial bodies including:
  • Asteroids
  • Planets
  • Stars
  • Black holes
  • White holes
  • AI Satellites
  • Player-controlled rocket ship

Technical details

The entire app is run under MainActivity.java. In order to show a UI stacked on top of a canvas (a custom view GameView), I had to use a RelativeLayout.

GameView sets up the simulation upon creation. It sets up and handles user input (e.g. touch, drag, pinch events). I also make use of enum objects to neatly keep track of the current user state (e.g. current type of celestial body selected, current placement type, etc).

A Universe object is created in the GameView constructor. It contains an array of all celestial bodies in the system. The universe also contains and operates the inner "machinery" of how objects interact with each other through the update() function. The update() function loops through all celestial bodies and calculates the net force exerted by every other object on it and performs integration to obtain new positions in a nested loop. It also checks any collisions between objects in this loop.

A CelestialBody is a superclass of all celestial objects that can be created. Every CelestialBody holds the physical properties of mass, radius, position, velocity, acceleration, and net force. Here's a list of all of the subclasses of CelestialBody:

• Asteroid: A small object with very low mass and radius. These objects move the fastest. During integration, we ignore the force exerted by these objects on other objects because it is negligible.
• Planet: An medium-sized object with considerable mass and radius. Place these objects in Orbit mode near a Star to simulate a solar system.
• Star: A large-sized object with high mass and radius. You may find it useful to place these in the Fixed placement mode when playing around with planets and asteroids.
• Black hole: A dense object with extremely high mass and low radius. These exert the highest gravitational force of all celestial bodies.
• White hole: A hypothetical celestial body that yields negative mass and therefore repels any other objects with positive mass with its negative gravitational force.
• Satellite: An artificial object that circles the celestial body that is currently exerting the most force applied to it. Try it out in a binary star system and watch how it moves!
• Player ship: An object that can be controlled by the player. Touch and drag to apply thrust in the desired direction. Note that the ship can only be controlled when the Player ship option is selected.

There are also some other helper classes that I made.

• Vector2D: A utility class that implements 2D vectors and common operations on vectors, such as finding the magnitude of its x and y components, the angle between a vector and another vector, distance between two vectors, and dot product of two vectors.
• MassRadiusTuple: A utility class used to encapsulate the mass and radius definitions of different types of celestial bodies and their size types.
• StarColors: A class that maps the B-V color index of different star colour/temperatures to their RGB values. The B-V index can be a minimum of -0.4 (hottest / blue) and a maximum of 2.0 (coolest / red). A StarColor object is created upon initialization of a ColorGenerator object.
• ColorGenerator: A class that controls the appropriate colours assigned to every type of celestial body. Only one ColorGenerator is created upon initialization of the simulation.