javascript - 如何将实体移动到鼠标位置并朝其旋转

Question

我正在阅读this tuts+ 上有关如何使用 CreateJS 让宇宙飞船跟随光标的文章， 我想知道如何使实体向鼠标位置移动但也面向它旋转。

这是一个fiddle没有旋转的示例 和代码

var canvas = document.getElementById("Canvas");
var ship;
var stage;
var assets;
var loader;
var serverString = "http://source.tutsplus.com/gamedev/authors/JamesTyner/SmoothMoves/";
var stageHeight = 600;
var stageWidth = 600;
var shipHeight = 64;
var shipWidth = 64;
var easingAmount = 0.15;
var text;
stage = new createjs.Stage(canvas);
assets = [];
manifest = [{
    src: serverString + "ship.png",
    id: "character"
}];

loader = new createjs.LoadQueue(false);
loader.onComplete = handleComplete;
loader.onFileLoad = handleFileLoad;
loader.loadManifest(manifest);

function handleFileLoad(event) {
    var id = event.item.id;
    var result = loader.getResult(id);
    ship = new createjs.Bitmap(result);
    ship.x = (stageWidth / 2) - shipWidth;
    ship.y = stageHeight - shipHeight;
    ship.regX = shipWidth/2;
    ship.regY = shipHeight/2;
}

function handleComplete() {
    stage.addChild(ship);
    text = new createjs.Text("Click To Activate", "20px Arial", "#000000");
    text.x = 200;
    text.y = stageHeight / 2;
    stage.addChild(text);
    stage.update();
}

stage.onMouseDown = function () {
    stage.removeChild(text);
    createjs.Ticker.addEventListener("tick", tick);
};

function tick(event) {
   var xDistance = stage.getStage().mouseX - ship.x;
   var yDistance = stage.getStage().mouseY - ship.y;
   var distance = Math.sqrt(xDistance * xDistance + yDistance * yDistance);
    if (distance > 1) {
        ship.x += xDistance * easingAmount;
        ship.y += yDistance * easingAmount;
    }
    stage.update();
}

谢谢大家

Answer 1

首先计算船舶与鼠标指针之间的 Angular (以度为单位):

var mousePointerPosition = {
        x: stage.getStage().mouseX,
        y: stage.getStage().mouseY
    };

var spaceShipPosition = {
        x: ship.x,
        y: ship.y
    };

var angle = Math.atan2(
        spaceShipPosition.y - mousePointerPosition.y,
        spaceShipPosition.x - mousePointerPosition.x
    ) * 180 / Math.PI;

然后旋转飞船:

ship.rotation = ( angle > 180 ? -angle : angle ) + 90;

如果 Angular 超过180，我们会反转 Angular 以使船转向另一个方向。另外，我还在 Angular 中添加了 + 90 ，因为与鼠标位置相比，船转动了 90 度。

Js fiddle :http://jsfiddle.net/nkZjR/200/