Asteroids Bullet Model

asteroids.bullet.js

/* 
* Below is a section of code for creating and moving bullets in a canvas rendered asteroids game.
* 
* Since asteroid ships can be facing a different direction than their movement direction, I needed
* to implement this model in a way that guaranteed bullets always fire in the direction the ship is facing.
*
* Multiple objects in the game are moveable, so code is simplified through Constructor inheritance. 
* 
* All functions are named for easier debugging
*/

/*
* The ship function that creates bullets:
*
* this.fire = function fire(){
*    return new ASTEROIDS.Model.Bullet({
*      x: this.x,
*      y: this.y,
*      vx: this.dx(this.direction, 5),
*      vy: this.dy(this.direction, 5),
*      direction: this.direction,
*    })
*  }
*
*/

ASTEROIDS.Model.Moveable = function Moveable(coords) {
  coords = coords || {};
  this.x = coords.x || ASTEROIDS.Model.height/2;
  this.y = coords.y || ASTEROIDS.Model.width/2;
  this.vx = coords.vx || 0;
  this.vy = coords.vy || 0;
}

ASTEROIDS.Model.Moveable.prototype.tic = function(){
  this.x += this.vx;
  this.y += this.vy;

  return this.x + ", " + this.y;
}
ASTEROIDS.Model.Moveable.prototype.dx = function(theta, radius){
  return (radius || this.radius) * Math.cos(theta)
}

ASTEROIDS.Model.Moveable.prototype.dy = function(theta, radius){
  return (radius || this.radius) * Math.sin(theta)
}


ASTEROIDS.Model.moveBullets = function moveBullets(){
  for(var i = 0; i < this.bullets.length; i++){
    this.bullets[i].setVertices();
    this.bullets[i].tic()
    if(this.screenWrap(this.bullets[i])){
      this.bullets.splice(i, 1)
    }
  }
}

ASTEROIDS.Model.Bullet = function Bullet(coords){

  this.direction = coords.direction;
  this.radius = 5;

  ASTEROIDS.Model.Moveable.call(this, coords);

  this.setVertices = function() {
    this.vertices = [
      [this.x + this.dx(this.direction), this.y + this.dy(this.direction)],
      [this.x + this.dx(this.direction + Math.PI), this.y + this.dy(this.direction + Math.PI)],
    ]
  }
}
ASTEROIDS.Model.Bullet.prototype = Object.create(ASTEROIDS.Model.Moveable.prototype);
ASTEROIDS.Model.Bullet.prototype.constructor = ASTEROIDS.Model.Bullet;