By Jitu Das (cdas) & Bertha Lam (chingwal)
CMU 15-237 Cross-platform Mobile Web Apps, Fall 2012
This game is a 2D shooter. You control a spaceship that can shoot bullets, rotate left and right, and move forwards and backwards. To shoot bullets, press/hold down the spacebar key. To rotate left or right, hold down the left or right arrow key respectively. To move forwards or backwards, hold down the up or down arrow key respectively.
You start off with 100 health. If you get hit by a bullet, you lose 5 health, and if you crash into an enemy spaceship, you lose 25 health.
For every enemy spaceship that you kill, your score goes up by 5 points. Your final score is the points you gain from killing enemy ships plus any remaining health you have.
There is a high scores table that stores the top 5 scores in a cookie, and users can input their name for their high score entries.
When the page is loaded, we create a new instance of the Game class and attach the appropriate screen objects. The screen objects are responsible for rendering and handling interaction for different parts of the game. We read in the configuration for each of the game levels from an array at the top of the javascript file and then generate a screen for each one. Then we start the game.
The Game class has a main loop which is run 60 times per second using an interval timer. The main loop asks the screen to update, and if the screen indicates that it wishes to be rendered then it calls the render function. The screens can listen for events and ask the game to change screens.
The Stage class is a screen that is responsible for gameplay. It renders the spaceships, bullets, explosions, score, health, etc. It also listens for key events and handles interactions accordingly.
Inheritance is used throughout our program to minimize duplicated code. There is a Screen class which gets extended to the different screens like Menu, Stage, and Instructions. There is also an Object class that gets extended into Bullet and SpaceShip. The SpaceShip is further extended into the Player class. Object has functions such as drawing the sprite associated with the object and common collision detection code. The SpaceShip class adds health and a shooting delay since these are common to the player as well as enemy ships.