Chapter 2: Tank Game Course

var TankGame = (function() {
  var TARGET_WIDTH = 801; // Desired width
  var TARGET_HEIGHT = 601;
  var WIDTH; // Actual width of game, scaled to fit screen
  var HEIGHT;
  var GUI_HEIGHT = 150;
  var DEBUG = false;
  // WASD
  var P1_UP = 87;
  var P1_DOWN = 83;
  var P1_LEFT = 65;
  var P1_RIGHT = 68;
  var P1_FIRE = 49;

  // Arrow keys
  var P2_UP = 38;
  var P2_DOWN = 40;
  var P2_LEFT = 37;
  var P2_RIGHT = 39;
  var P2_FIRE = 189;

  // Other settings
  var TANK_SIZE = 15;
  var TANK_SPEED = 1;
  var TANK_TURN_SPEED = 5;
  var WALL_WIDTH = 2;
  var CELL_SIZE = 50;
  var RESET_COUNTER_MAX = 200;
  var EPSILON = 0.001;


  var MAX_DIST_FOR_COLLISIONS = 2; // (this is multiplied by CELL_SIZE)
  var TANK_P1, TANK_P2;
  var CELLS_X, CELLS_Y;
  var CANVAS, CTX, KEYSTATE, GAME_OBJECTS;
  var PRERENDERED_CANVAS, PRERENDERED_CTX, PRERENDERED_REDRAW_NEEDED;
  var GUI_REDRAW_NEEDED;
  var END_ROUND = false;
  var RESET_COUNTER;

  var P1 = 1;
  var P2 = 2;
  var P1_SCORE = 0;
  var P2_SCORE = 0;




  /*
  ===============================================================================
  -------------------------------------CLASSES-----------------------------------
  ===============================================================================
  */

  function deg2rad(degrees) {
    return degrees * (Math.PI/180);
  }

  class Vector2d {
    constructor(x, y) {
      if (typeof x == 'undefined' || typeof  y == 'undefined') {
        throw "Invalid arguments";
      }
      this.x = x;
      this.y = y;
    }

    rotate(radians) {
      // Rotates coordinates counterclockwise
      //radians=-radians
      if (radians != 0) {
        var x = this.x;
        var y = this.y;
        this.x = x * Math.cos(radians) - y * Math.sin(radians);
        this.y = x * Math.sin(radians) + y * Math.cos(radians);
      }
      return this;
    }

    add(vector) {
      if (vector instanceof Vector2d) {
        this.x += vector.x;
        this.y += vector.y;
      }
      else throw "Invalid argument";
      return this;
    }

    subtract(vector) {
      if (vector instanceof Vector2d) {
        this.x -= vector.x;
        this.y -= vector.y;
      }
      else throw "Invalid argument";
      return this;
    }

    multiply(value) {
      if (isNaN(value) === false) {
        this.x *= value;
        this.y *= value;
      }
      else throw "Invalid argument";
      return this;
    }

    get_dot_product(other) {
      if (other instanceof Vector2d) return this.x*other.x + this.y*other.y;
      else throw "Invalid argument";
    }

    get_unit_vector() {
      var c = this.get_magnitude();
      var unit_vec = new Vector2d(this.x/c, this.y/c);
      return unit_vec;
    }

    get_right_normal() {
      return new Vector2d(this.y, -this.x);
    }

    get_magnitude() {
      return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
    }

    get_magnitude_squared() {
      return Math.pow(this.x, 2) + Math.pow(this.y, 2);
    }

    get_inverted() {
      return new Vector2d(-this.x, -this.y);
    }

    clone() {
      return new Vector2d(this.x, this.y);
    }

    reflect(vector) {
      if (vector instanceof Vector2d) {
        var vec2 = vector.clone(); // Avoid modifying given vector
        vec2.multiply(vec2.get_dot_product(this));
        vec2.multiply(2);
        this.subtract(vec2);
        return this;
      }
      else throw "Invalid argument";
    }
  };