Cesium基础知识-添加云特效

1. //加载云特效
2. function LoadClouds() {
3.     const worldRectangle1 = viewer.scene.primitives.add(new Cesium.Primitive({
4.         geometryInstances: new Cesium.GeometryInstance({
5.             geometry: new Cesium.RectangleGeometry({
6.                 rectangle: Cesium.Rectangle.fromDegrees(-180.0, -90.0, 180.0, 90.0),
7.                 vertexFormat: Cesium.EllipsoidSurfaceAppearance.VERTEX_FORMAT
8.             })
9.         }),
10.         appearance: new Cesium.EllipsoidSurfaceAppearance({
11.             material: new Cesium.Material({
12.                 fabric: {
13.                     type: 'Image',
14.                     uniforms: {
15.                         image: '../../img/clouds.png',
16.                         radians: 0,
17.                     },
18.                     //shader
19.                     source: `
20.               #define M_PI 3.1415926535897932384626433832795
21.   
22.               uniform sampler2D image;
23.               uniform float radians;
24.               
25.               czm_material czm_getMaterial(czm_materialInput materialInput)
26.               {
27.                 czm_material material = czm_getDefaultMaterial(materialInput);
28.                 vec2 st = vec2(materialInput.st.x - 0.5, materialInput.st.y - 0.5);
29.                 float alpha = 1.3 - st.x - 0.5;
30.                 float current_radians = atan(st.y, st.x);
31.                 float radius = sqrt(st.x * st.x + st.y * st.y);
32.                 if (radius < 0.50) {
33.                   current_radians = current_radians - radians;
34.                   st = vec2(cos(current_radians) * radius, sin(current_radians) * radius);
35.                   st = vec2(st.x + 0.5, st.y + 0.5);
36.                   vec4 colorImage = texture2D(image, st);
37.                   material.diffuse = colorImage.rgb;
38.                   material.alpha = colorImage.a * alpha;
39.                 } else {
40.                   material.alpha = 0.0;
41.                 }
42.   
43.                 return material;
44.               }
45.               `
46.                 }
47.             }),
49.             aboveGround: true
50.         }),
51.         show: true
52.     }))
53.     var radians = 0
54.     viewer.scene.postRender.addEventListener(() => {
55.         radians += Math.PI / 50000;
56.         worldRectangle1.appearance.material.uniforms.radians = radians;
57.     });
58. }
59. LoadClouds();