键盘移动

只需再做一点微小的工作，你就可以建立一个通过鼠标控制精灵移动的简单系统。为了简化你的代码，我建议你用一个名为keyboard的自定义函数来监听和捕捉键盘事件。

function keyboard(keyCode) {
  let key = {};
  key.code = keyCode;
  key.isDown = false;
  key.isUp = true;
  key.press = undefined;
  key.release = undefined;
  //The `downHandler`
  key.downHandler = event => {
    if (event.keyCode === key.code) {
      if (key.isUp && key.press) key.press();
      key.isDown = true;
      key.isUp = false;
    }
    event.preventDefault();
  };
  //The `upHandler`
  key.upHandler = event => {
    if (event.keyCode === key.code) {
      if (key.isDown && key.release) key.release();
      key.isDown = false;
      key.isUp = true;
    }
    event.preventDefault();
  };
  //Attach event listeners
  window.addEventListener(
    "keydown", key.downHandler.bind(key), false
  );
  window.addEventListener(
    "keyup", key.upHandler.bind(key), false
  );
  return key;
}

keyboard函数用起来很容易，可以像这样创建一个新的键盘对象：

let keyObject = keyboard(asciiKeyCodeNumber);

这个函数只接受一个参数就是键盘对应的ASCII键值数，也就是你想监听的键盘按键。 这是键盘键ASSII值列表).

然后给键盘对象赋值press和release方法：

keyObject.press = () => {
  //key object pressed
};
keyObject.release = () => {
  //key object released
};

键盘对象也有 isDown 和 isUp 的布尔值属性，你可以用它们来检查每个按键的状态。

在examples文件夹里看一下keyboardMovement.html文件是怎么用keyboard函数的，利用键盘的方向键去控制精灵图。运行它，然后用上下左右按键去让猫在舞台上移动。

这里是代码：

//Define any variables that are used in more than one function
let cat, state;
function setup() {
  //Create the `cat` sprite
  cat = new Sprite(resources["images/cat.png"].texture);
  cat.y = 96;
  cat.vx = 0;
  cat.vy = 0;
  app.stage.addChild(cat);
  //Capture the keyboard arrow keys
  let left = keyboard(37),
      up = keyboard(38),
      right = keyboard(39),
      down = keyboard(40);
  //Left arrow key `press` method
  left.press = () => {
    //Change the cat's velocity when the key is pressed
    cat.vx = -5;
    cat.vy = 0;
  };
  //Left arrow key `release` method
  left.release = () => {
    //If the left arrow has been released, and the right arrow isn't down,
    //and the cat isn't moving vertically:
    //Stop the cat
    if (!right.isDown && cat.vy === 0) {
      cat.vx = 0;
    }
  };
  //Up
  up.press = () => {
    cat.vy = -5;
    cat.vx = 0;
  };
  up.release = () => {
    if (!down.isDown && cat.vx === 0) {
      cat.vy = 0;
    }
  };
  //Right
  right.press = () => {
    cat.vx = 5;
    cat.vy = 0;
  };
  right.release = () => {
    if (!left.isDown && cat.vy === 0) {
      cat.vx = 0;
    }
  };
  //Down
  down.press = () => {
    cat.vy = 5;
    cat.vx = 0;
  };
  down.release = () => {
    if (!up.isDown && cat.vx === 0) {
      cat.vy = 0;
    }
  };
  //Set the game state
  state = play;
  //Start the game loop
  app.ticker.add(delta => gameLoop(delta));
}
function gameLoop(delta){
  //Update the current game state:
  state(delta);
}
function play(delta) {
  //Use the cat's velocity to make it move
  cat.x += cat.vx;
  cat.y += cat.vy
}