javascript - HTML5 Javascript 旋转

Question

我是 JavaScript（和编程）的新手，并且正在努力解决如何在 HTML5 Canvas 中添加旋转。我基本上是想让 JavaScript 对象围绕另一个对象旋转。就我而言，我需要让一颗行星围绕太阳运行。

我目前在绘图函数中声明了行星，它们显示得很好。我只需要有关如何添加旋转的帮助。

谢谢你的时间。

Answer 1

这是一个简单的例子：http: //jsfiddle.net/FTMCv/1/

CelestialBody我创建的类只考虑圆形轨道，所以它不是一个完美的模拟，但在大多数情况下它可能就足够了。

(function(){

    var can = document.getElementById('planetarium'),
        ctx = can.getContext('2d'),
        bodies = [];


    (function init(){
        var orbCenter = {x:can.width/2, y:can.height/2};

        bodies.push(new CelestialBody(
            50, orbCenter , 0, 0));

        bodies.push(new CelestialBody(
            15, orbCenter , 250, -.2));
        bodies.push(new CelestialBody(
            6, orbCenter , 200, .3));
        bodies.push(new CelestialBody(
            7, orbCenter , 150, .5));
        bodies.push(new CelestialBody(
            5, orbCenter , 100, 1));
        bodies.push(new CelestialBody(
            4, orbCenter , 75, 3));
    })();

    function CelestialBody(radius, orbitalCenter, orbitalDistance, orbitalVelocity){
        var pos = {x:0, y:0},
            rad = radius,
            orb = {x: orbitalCenter.x, y:orbitalCenter.y},
            ove = orbitalVelocity,
            odi = orbitalDistance;

        var update = function(){
            var cAng = Math.atan2(pos.y - orb.y, pos.x - orb.x);
            var rAng = cAng + ove * Math.PI/180;

            pos.x = orb.x + Math.cos(rAng) * odi;
            pos.y = orb.y + Math.sin(rAng) * odi;
        };

        this.draw = function(ctx){
            update();

            ctx.beginPath();
            ctx.fillStyle = "#fff";
            ctx.arc(pos.x,pos.y, rad, 0, 2*Math.PI);
            ctx.fill();
        };

        (function init(){
            pos.y = orb.y;
            pos.x = orb.x + odi;
        })();
    }

    (function draw(){
        ctx.clearRect(0,0,can.width,can.height);

        for(var i = 0; i < bodies.length; i++)
            bodies[i].draw(ctx);

        webkitRequestAnimationFrame(draw);
    })();

})();​