使用threejs实现地球辉光和大气层效果

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使用threejs实现地球辉光和大气层效果

实现原理就是使用three.js的ShaderMaterial材质。
我们把辉光分为几个步骤来实现：

1. 创建两个球体，一个作为原始物体，一个略大一些作为它的辉光
2. 作为辉光的球体从内到外片元透明度逐渐减小（线性减小或是指数减小都可以）
3. 将覆盖原始物体的部分丢弃掉

主要代码如下：

var vertexShader = [
    'varying vec3	vVertexWorldPosition;',
    'varying vec3	vVertexNormal;',
    'varying vec4	vFragColor;',
    'void main(){',
    '	vVertexNormal	= normalize(normalMatrix * normal);',//将法线转换到视图坐标系中
    '	vVertexWorldPosition	= (modelMatrix * vec4(position, 1.0)).xyz;',//将顶点转换到世界坐标系中
    '	// set gl_Position',
    '	gl_Position	= projectionMatrix * modelViewMatrix * vec4(position, 1.0);',
    '}'

].join('\n');
//大气层效果
THREE.AeroSphere = {
    uniforms: {
        coeficient: {
            type: "f",
            value: 1.0
        },
        power: {
            type: "f",
            value: 2
        },
        glowColor: {
            type: "c",
            value: new THREE.Color(0xffff00)
        }
    },
    vertexShader: vertexShader,
    fragmentShader: [
        'uniform vec3	glowColor;',
        'uniform float	coeficient;',
        'uniform float	power;',

        'varying vec3	vVertexNormal;',
        'varying vec3	vVertexWorldPosition;',

        'varying vec4	vFragColor;',

        'void main(){',
        '	vec3 worldCameraToVertex= vVertexWorldPosition - cameraPosition;',	//世界坐标系中从相机位置到顶点位置的距离
        '	vec3 viewCameraToVertex	= (viewMatrix * vec4(worldCameraToVertex, 0.0)).xyz;',//视图坐标系中从相机位置到顶点位置的距离
        '	viewCameraToVertex	= normalize(viewCameraToVertex);',//规一化
        '	float intensity		= pow(coeficient + dot(vVertexNormal, viewCameraToVertex), power);',
        '	gl_FragColor		= vec4(glowColor, intensity);',
        '}'//vVertexNormal视图坐标系中点的法向量
        //viewCameraToVertex视图坐标系中点到摄像机的距离向量
        //dot点乘得到它们的夹角的cos值
        //从中心向外面角度越来越小（从钝角到锐角）从cos函数也可以知道这个值由负变正，不透明度最终从低到高
    ].join('\n')

//辉光效果Grow
THREE.GlowSphere = {
    uniforms: {
        coeficient: {
            type: "f",
            value: 0.0
        },
        power: {
            type: "f",
            value: 2
        },
        glowColor: {
            type: "c",
            value: new THREE.Color(0xff22ff)
        }
    },
    vertexShader: vertexShader,
    fragmentShader: [
        'uniform vec3	glowColor;',
        'uniform float	coeficient;',
        'uniform float	power;',

        'varying vec3	vVertexNormal;',
        'varying vec3	vVertexWorldPosition;',

        'varying vec4	vFragColor;',

        'void main(){',
        '	vec3 worldVertexToCamera= cameraPosition - vVertexWorldPosition;',	//世界坐标系中顶点位置到相机位置到的距离
        '	vec3 viewCameraToVertex	= (viewMatrix * vec4(worldVertexToCamera, 0.0)).xyz;',//视图坐标系中从相机位置到顶点位置的距离
        '	viewCameraToVertex	= normalize(viewCameraToVertex);',//规一化
        '	float intensity		= coeficient + dot(vVertexNormal, viewCameraToVertex);',
        '	if(intensity > 0.65){ intensity = 0.0;}',
        '	gl_FragColor		= vec4(glowColor, intensity);',
        '}'//vVertexNormal视图坐标系中点的法向量
        //viewCameraToVertex视图坐标系中点到摄像机的距离向量
        //dot点乘得到它们的夹角的cos值
        //从中心向外面角度越来越大（从锐角到钝角）从cos函数也可以知道这个值由负变正，不透明度最终从高到低
    ].join('\n')
}

//球体 辉光 大气层
    function shad() {        
        var material1 = new THREE.ShaderMaterial({
            uniforms: THREE.AeroSphere.uniforms,
            vertexShader: THREE.AeroSphere.vertexShader,
            fragmentShader: THREE.AeroSphere.fragmentShader,
            blending: THREE.NormalBlending,
            transparent: true,
            depthWrite:false
        });
        var material2 = new THREE.ShaderMaterial({
            uniforms: THREE.GlowSphere.uniforms,
            vertexShader: THREE.GlowSphere.vertexShader,
            fragmentShader: THREE.GlowSphere.fragmentShader,
            blending: THREE.NormalBlending,
            transparent: true
        });
        var sphere = new THREE.SphereBufferGeometry(16, 32, 32);
        var mesh = new THREE.Mesh(sphere, material1);
        scene.add(mesh);

        var sphere2 = new THREE.SphereBufferGeometry(10, 32, 32);
        var mesh2 = new THREE.Mesh(sphere2, material2);
        //mesh2.position.x = 15;
        scene.add(mesh2);
    }

效果如下图所示：

代码参考：https://blog.csdn.net/srk19960903/article/details/78734238