cesium 自定义贴图，shadertoy移植教程。

1.前言

cesium中提供了一些高级的api，可以自己写一些shader来制作炫酷的效果。
ShaderToy 是一个可以在线编写、测试和分享图形渲染着色器的网站。它提供了一个图形化的编辑器，可以让用户编写基于 WebGL 的 GLSL 着色器代码，并实时预览渲染结果。

ShaderToy 支持多种渲染效果，包括 2D 和 3D 图形、粒子系统、动画等。用户可以通过调整着色器代码中的参数来实现各种不同的视觉效果。
此外，ShaderToy 还提供了一个社区功能，用户可以分享自己的着色器作品，并与其他用户进行交流和学习。这个社区中有很多优秀的着色器作品，涵盖了各种不同的主题和风格。
总之，ShaderToy 是一个非常有趣和实用的工具，它为图形学爱好者提供了一个学习和创作的平台，同时也为 WebGL 开发者提供了一个快速测试和演示的工具。
现在我们抽取一个简单的额shadertoy例子在cesium中实现。

2.效果图

在这里插入图片描述

3.示例代码

const viewer = new Cesium.Viewer("cesiumContainer");
/*
 * @Description: 电弧球体效果（参考开源代码）
 * @Version: 1.0
 * @Author: Julian
 * @Date: 2022-03-04 15:57:40
 * @LastEditors: Julian
 * @LastEditTime: 2022-03-04 16:20:31
 */
class EllipsoidElectricMaterialProperty {
    constructor(options) {
        this._definitionChanged = new Cesium.Event();
        this._color = undefined;
        this._speed = undefined;
        this.color = options.color;
        this.speed = options.speed;
    }

    get isConstant() {
        return false;
    }

    get definitionChanged() {
        return this._definitionChanged;
    }

    getType(time) {
        return Cesium.Material.EllipsoidElectricMaterialType;
    }

    getValue(time, result) {
        if (!Cesium.defined(result)) {
            result = {};
        }

        result.color = Cesium.Property.getValueOrDefault(this._color, time, Cesium.Color.RED, result.color);
        result.speed = Cesium.Property.getValueOrDefault(this._speed, time, 10, result.speed);
        return result;
    }

    equals(other) {
        return (this === other ||
            (other instanceof EllipsoidElectricMaterialProperty &&
                Cesium.Property.equals(this._color, other._color) &&
                Cesium.Property.equals(this._speed, other._speed)));
    }
}

Object.defineProperties(EllipsoidElectricMaterialProperty.prototype, {
    color: Cesium.createPropertyDescriptor('color'),
    speed: Cesium.createPropertyDescriptor('speed')
});

Cesium.EllipsoidElectricMaterialProperty = EllipsoidElectricMaterialProperty;
Cesium.Material.EllipsoidElectricMaterialProperty = 'EllipsoidElectricMaterialProperty';
Cesium.Material.EllipsoidElectricMaterialType = 'EllipsoidElectricMaterialType';
Cesium.Material.EllipsoidElectricMaterialSource =
    `
	#define UVScale 			 0.4
#define Speed				 0.6

#define FBM_WarpPrimary		-0.24
#define FBM_WarpSecond		 0.29
#define FBM_WarpPersist 	 0.78
#define FBM_EvalPersist 	 0.62
#define FBM_Persistence 	 0.5
#define FBM_Lacunarity 		 2.2
#define FBM_Octaves 		 5
//fork from Dave Hoskins
//https://www.shadertoy.com/view/4djSRW
vec4 hash43(vec3 p)
{
	vec4 p4 = fract(vec4(p.xyzx) * vec4(1031, .1030, .0973, .1099));
    p4 += dot(p4, p4.wzxy+19.19);
	return -1.0 + 2.0 * fract(vec4(
        (p4.x + p4.y)*p4.z, (p4.x + p4.z)*p4.y,
        (p4.y + p4.z)*p4.w, (p4.z + p4.w)*p4.x)
    );
}

//offsets for noise
const vec3 nbs[] = vec3[8] (
    vec3(0.0, 0.0, 0.0),vec3(0.0, 1.0, 0.0),vec3(1.0, 0.0, 0.0),vec3(1.0, 1.0, 0.0),
    vec3(0.0, 0.0, 1.0),vec3(0.0, 1.0, 1.0),vec3(1.0, 0.0, 1.0),vec3(1.0, 1.0, 1.0)
);

//'Simplex out of value noise', forked from: https://www.shadertoy.com/view/XltXRH
//not sure about performance, is this faster than classic simplex noise?
vec4 AchNoise3D(vec3 x)
{
    vec3 p = floor(x);
    vec3 fr = smoothstep(0.0, 1.0, fract(x));

    vec4 L1C1 = mix(hash43(p+nbs[0]), hash43(p+nbs[2]), fr.x);
    vec4 L1C2 = mix(hash43(p+nbs[1]), hash43(p+nbs[3]), fr.x);
    vec4 L1C3 = mix(hash43(p+nbs[4]), hash43(p+nbs[6]), fr.x);
    vec4 L1C4 = mix(hash43(p+nbs[5]), hash43(p+nbs[7]), fr.x);
    vec4 L2C1 = mix(L1C1, L1C2, fr.y);
    vec4 L2C2 = mix(L1C3, L1C4, fr.y);
    return mix(L2C1, L2C2, fr.z);
}

vec4 ValueSimplex3D(vec3 p)
{
	vec4 a = AchNoise3D(p);
	vec4 b = AchNoise3D(p + 120.5);
	return (a + b) * 0.5;
}

//my FBM
vec4 FBM(vec3 p)
{
    vec4 f, s, n = vec4(0.0);
    float a = 1.0, w = 0.0;
    for (int i=0; i<FBM_Octaves; i++)
    {
        n = ValueSimplex3D(p);
        f += (abs(n)) * a;	//billowed-like
        s += n.zwxy *a;
        a *= FBM_Persistence;
        w *= FBM_WarpPersist;
        p *= FBM_Lacunarity;
        p += n.xyz * FBM_WarpPrimary *w;
        p += s.xyz * FBM_WarpSecond;
        p.z *= FBM_EvalPersist +(f.w *0.5+0.5) *0.015;
    }
    return f;
}
	
	czm_material czm_getMaterial(czm_materialInput materialInput)
	{
	czm_material material = czm_getDefaultMaterial(materialInput);
	vec2 st = materialInput.st;

    
    vec4 fbm = (FBM(vec3(st, czm_frameNumber * speed +100.0)));
    float explosionGrad = (dot(fbm.xyzw, fbm.yxwx)) *0.5;
    explosionGrad = pow(explosionGrad, 1.3);
    explosionGrad = smoothstep(0.0,1.0,explosionGrad);
    #define color0 vec3(1.2,0.0,0.0)
    #define color1 vec3(0.9,0.7,0.3)

	material.diffuse = explosionGrad * mix(color0, color1, explosionGrad) *1.2 +0.05;;
	material.alpha = 1.0;
	return material;
	}
	`;

Cesium.Material._materialCache.addMaterial(Cesium.Material.EllipsoidElectricMaterialType, {
    fabric: {
        type: Cesium.Material.EllipsoidElectricMaterialType,
        uniforms: {
            color: new Cesium.Color(1.0, 0.0, 0.0, 1.0),
            speed: 10.0
        },
        source: Cesium.Material.EllipsoidElectricMaterialSource
    },
    translucent: function(material) {
        return true;
    }
});
const entity=viewer.entities.add({
    position: Cesium.Cartesian3.fromDegrees(113.9236839, 22.528061),
    ellipsoid: {
        radii: new Cesium.Cartesian3(1000.0, 1000.0, 1000.0),
        material: new Cesium.EllipsoidElectricMaterialProperty({
            color: new Cesium.Color(1.0, 1.0, 0.0, 1.0),
            speed: 0.01
        })
    }
});
viewer.flyTo(entity);