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16.3 A Monster (Eloquent JavaScript Solutions)
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| <link rel="stylesheet" href="css/game.css"> | |
| <style>.monster { background: purple }</style> | |
| <body> | |
| <script> | |
| // Complete the constructor, update, and collide methods | |
| class Monster { | |
| constructor(pos, speed, chase) { | |
| this.pos = pos; | |
| this.speed = speed; | |
| this.chase = chase; | |
| } | |
| get type() { return "monster"; } | |
| static create(pos, ch) { | |
| if (ch == 'm') { | |
| // monster that moves back and forth | |
| return new Monster(pos.plus(new Vec(0, -1)), new Vec(3, 0), false); | |
| } else { // 'M' | |
| // monster that chases player | |
| return new Monster(pos.plus(new Vec(0, -1)), new Vec(3, 0), true); | |
| } | |
| } | |
| update(time, state) { | |
| let newPos; | |
| if (this.chase) { | |
| if (state.player.pos.x < this.pos.x) { | |
| this.speed = new Vec(-3, 0); | |
| } else { | |
| this.speed = new Vec(3, 0); | |
| } | |
| } | |
| newPos = this.pos.plus(this.speed.times(time)); | |
| if (!state.level.touches(newPos, this.size, "wall")) { | |
| return new Monster(newPos, this.speed, this.chase); | |
| } else { | |
| return new Monster(this.pos, this.speed.times(-1), this.chase); | |
| } | |
| } | |
| collide(state) { | |
| let player = state.player; | |
| let monster = this; | |
| if (monster.pos.y - player.pos.y > 1) { | |
| let filtered = state.actors.filter(a => a != this); | |
| return new State(state.level, filtered, state.status); | |
| } else { | |
| return new State(state.level, state.actors, 'lost'); | |
| } | |
| } | |
| } | |
| Monster.prototype.size = new Vec(1.2, 2); | |
| levelChars["m"] = Monster; | |
| levelChars["M"] = Monster; | |
| runLevel(new Level(` | |
| .................................. | |
| .################################. | |
| .#..............................#. | |
| .#..............................#. | |
| .#..............................#. | |
| .#...........................o..#. | |
| .#..@...........................#. | |
| .##########..............########. | |
| ..........#..o..o..o..o..#........ | |
| ..........#..m........M..#........ | |
| ..........################........ | |
| .................................. | |
| `), DOMDisplay); | |
| </script> | |
| </body> |
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Hints
If you want to implement a type of motion that is stateful, such as bouncing, make sure you store the necessary state in the actor object—include it as a constructor argument and add it as a property.
Remember that
updatereturns a new object, rather than changing the old one.When handling collision, find the player in
state.actorsand compare its position to the monster’s position. To get the bottom of the player, you have to add its vertical size to its vertical position. The creation of an updated state will resemble eitherCoin’scollidemethod (removing the actor) orLava’s (changing the status to"lost"), depending on the player position.