three 实现绕物体旋转，卫星绕星球旋转

1.先看看效果
2.如果是二维的话，可以根据变化角度结合三角函数就能计算从x和y坐标；
无奈，如果还是使用坐标改变的方式，博主不会三维数学啊，计算不出x,y和z坐标啊。
还好，过了好长时间，博主终于在网上找到了解决的方法，
就是把中心点，圆环(圆轨)和卫星三者组合成一体，再改变旋转角度
3.代码如下
<!DOCTYPE html>  
<html lang="en">  
<head>  
    <meta charset="UTF-8">  
    <title>TestRound</title>  
    <style type="text/css">  
        html, body {  
            width: 100%;  
            height: 100%;  
            margin: 0;  
            background-color: black;  
        }  
  
        div#box {  
            width: 100%;  
            height: 100%;  
        }  
    </style>  
    <script type="text/javascript" src="../../js/resource/js/three/three.js"></script>  
</head>  
<body onload="initThree()">  
<div id="box"></div>  
</body>  
<script>  
    var renderer, camera, scene;//渲染器，相加，场景  
    var Earth, satellites = [];//地球，卫星（数组）  
  
    function initThree() {  
        var dom = document.getElementById("box");  
  
        scene = new THREE.Scene();  
        camera = new THREE.PerspectiveCamera(20, dom.clientWidth / dom.clientHeight, 1, 1000);  
        camera.position.set(0, 0, 400);//设置相机位置  
        renderer = new THREE.WebGLRenderer({  
            alpha: true,  
            antialias: true  
        });  
        renderer.setSize(dom.clientWidth, dom.clientHeight);//设置窗口尺寸  
        dom.appendChild(renderer.domElement);  
  
        var sunTexture = THREE.ImageUtils.loadTexture('../../js/resource/img/map_world.png', {}, function () {  
            renderer.render(scene, camera);  
        });  
  
        //地球  
        Earth = new THREE.Mesh(new THREE.SphereGeometry(20, 30, 30), new THREE.MeshBasicMaterial({  
            map: sunTexture  
        })); //材质设定  
  
        var satellite = new THREE.Sprite(new THREE.SpriteMaterial({  
            map: new THREE.CanvasTexture(generateSprite('196,233,255')),  
            blending: THREE.AdditiveBlending  
        }));  
        satellite.scale.x = satellite.scale.y = satellite.scale.z = 60;  
        scene.add(satellite);//添加发光,让地球有发光的样式  
        scene.add(Earth);  
  
        //添加卫星  
        satellites.push(initSatellite(5, 28, {x: -Math.PI * 0.35, y: Math.PI * 0.25, z: 0}, 0.021, scene));  
        satellites.push(initSatellite(5, 25, {x: -Math.PI * 0.35, y: -Math.PI * 0.2, z: 0}, 0.022, scene));  
        satellites.push(initSatellite(5, 29, {x: -Math.PI * 0.35, y: Math.PI * 0.05, z: 0}, 0.023, scene));  
  
        render();  
  
    }  
  
      
    /**  
     * 返回一个卫星和轨道的组合体  
     * @param satelliteSize 卫星的大小  
     * @param satelliteRadius 卫星的旋转半径  
     * @param rotation 组合体的x,y,z三个方向的旋转角度  
     * @param speed 卫星运动速度  
     * @param scene 场景  
     * @returns {{satellite: THREE.Mesh, speed: *}} 卫星组合对象;速度  
     */  
    var initSatellite = function (satelliteSize, satelliteRadius, rotation, speed, scene) {  
  
        var track = new THREE.Mesh(new THREE.RingGeometry(satelliteRadius, satelliteRadius + 0.05, 50, 1), new THREE.MeshBasicMaterial());  
        var centerMesh = new THREE.Mesh(new THREE.SphereGeometry(1, 1, 1), new THREE.MeshLambertMaterial()); //材质设定  
        var satellite = new THREE.Sprite(new THREE.SpriteMaterial({  
            map: new THREE.CanvasTexture(generateSprite('196,233,255')),  
            blending: THREE.AdditiveBlending  
        }));  
        satellite.scale.x = satellite.scale.y = satellite.scale.z = satelliteSize;  
        satellite.position.set(satelliteRadius, 0, 0);  
  
        var pivotPoint = new THREE.Object3D();  
        pivotPoint.add(satellite);  
        pivotPoint.add(track);  
        centerMesh.add(pivotPoint);  
        centerMesh.rotation.set(rotation.x, rotation.y, rotation.z);  
        scene.add(centerMesh);  
        return {satellite: centerMesh, speed: speed};  
    };  
  
    /**  
     * 实现发光星星  
     * @param color 颜色的r,g和b值,比如：“123,123,123”;  
     * @returns {Element} 返回canvas对象  
     */  
    var generateSprite = function (color) {  
        var canvas = document.createElement('canvas');  
        canvas.width = 16;  
        canvas.height = 16;  
        var context = canvas.getContext('2d');  
        var gradient = context.createRadialGradient(canvas.width / 2, canvas.height / 2, 0, canvas.width / 2, canvas.height / 2, canvas.width / 2);  
        gradient.addColorStop(0, 'rgba(' + color + ',1)');  
        gradient.addColorStop(0.2, 'rgba(' + color + ',1)');  
        gradient.addColorStop(0.4, 'rgba(' + color + ',.6)');  
        gradient.addColorStop(1, 'rgba(0,0,0,0)');  
        context.fillStyle = gradient;  
        context.fillRect(0, 0, canvas.width, canvas.height);  
        return canvas;  
    };  
      
  
    function render() {  
        renderer.render(scene, camera);  
        Earth.rotation.y -= 0.01;  
        for (var i = 0; i < satellites.length; i++) {  
            satellites[i].satellite.rotation.z -= satellites[i].speed;  
        }  
        requestAnimationFrame(render);  
    }  
  
</script>  
  
</html>
three 实现绕物体旋转，卫星绕星球旋转

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