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three.js 实现火花特效

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前言

大家好,这里是 CSS兼WebGL 魔法使——alphardex。

上周末刚在原神里抽到了“火花骑士”可莉,于是就心血来潮,想用three.js来实现一种火系的特效,不是炸弹的爆炸,而是炸弹爆炸后在草上留下的火花效果

RBvmVJ.jpg

游戏里的效果相对比较卡通化,而本文的效果将更加逼近现实一点

让我们开始吧!

准备工作

在开始本项目之前,你首先要了解ray marching这个概念,如果不了解也没关系,笔者之前写过一篇介绍它的入门文章,或者通过这篇文章也可以入门,掌握了基础概念后就可以开始了

本项目需要用到:

笔者的three.js模板:点击右下角的fork即可复制一份

着色器模块化:glslify

着色器npm包:glsl-noise,glsl-sdf-primitives,glsl-sdf-ops

正文

场景搭建

按之前的惯例,搭建一个场景,放一个铺满屏幕的平面,设定一些必要的参数(火花的速度与颜色)

class RayMarchingFire extends Base {
  constructor(sel: string, debug: boolean) {
    super(sel, debug);
    this.clock = new THREE.Clock();
    this.cameraPosition = new THREE.Vector3(0, 0, 1);
    this.params = {
      velocity: 2,
    };
    this.colorParams = {
      color1: "#ff801a",
      color2: "#ff5718",
    };
  }
  // 初始化
  init() {
    this.createScene();
    this.createOrthographicCamera();
    this.createRenderer();
    this.createRayMarchingFireMaterial();
    this.createPlane();
    this.createLight();
    this.trackMousePos();
    this.addListeners();
    this.setLoop();
  }
  // 创建材质
  createRayMarchingFireMaterial() {
    const rayMarchingFireMaterial = new THREE.ShaderMaterial({
      vertexShader: rayMarchingFireVertexShader,
      fragmentShader: rayMarchingFireFragmentShader,
      side: THREE.DoubleSide,
      uniforms: {
        uTime: {
          value: 0,
        },
        uMouse: {
          value: new THREE.Vector2(0, 0),
        },
        uResolution: {
          value: new THREE.Vector2(window.innerWidth, window.innerHeight),
        },
        uVelocity: {
          value: 3,
        },
        uColor1: {
          value: new THREE.Color(this.colorParams.color1),
        },
        uColor2: {
          value: new THREE.Color(this.colorParams.color2),
        },
      },
    });
    this.rayMarchingFireMaterial = rayMarchingFireMaterial;
    this.shaderMaterial = rayMarchingFireMaterial;
  }
  // 创建平面
  createPlane() {
    const geometry = new THREE.PlaneBufferGeometry(2, 2, 100, 100);
    const material = this.rayMarchingFireMaterial;
    this.createMesh({
      geometry,
      material,
    });
  }
  // 动画
  update() {
    const elapsedTime = this.clock.getElapsedTime();
    const mousePos = this.mousePos;
    if (this.rayMarchingFireMaterial) {
      this.rayMarchingFireMaterial.uniforms.uTime.value = elapsedTime;
      this.rayMarchingFireMaterial.uniforms.uMouse.value = mousePos;
    }
  }
}
复制代码

接下来开始编写片元着色器

创建发光渐变椭圆

仔细观察火花的形状你会发现其实它的大致形状像一个椭圆,而且还是发光的渐变椭圆,于是我们就要想办法来创建这种形状。 简要说下思路:ray marching获取的值改成光线位置pos和光线移动的进度strength,光线位置的y轴将用于设定火花的颜色;光线移动的进度strength用于设定火花的形状(这里就是椭圆)

#pragma glslify:centerUv=require(../modules/centerUv)
#pragma glslify:getRayDirection=require(../modules/getRayDirection)
#pragma glslify:sdSphere=require(glsl-sdf-primitives/sdSphere)
#pragma glslify:opU=require(glsl-sdf-ops/union)
#pragma glslify:cnoise=require(glsl-noise/classic/3d)

uniform float uTime;
uniform vec2 uMouse;
uniform vec2 uResolution;
uniform float uVelocity;
uniform vec3 uColor1;
uniform vec3 uColor2;

varying vec2 vUv;
varying vec3 vPosition;

float fire(vec3 p){
    vec3 p2=p*vec3(1.,.5,1.)+vec3(0.,1.,0.);
    float geo=sdSphere(p2,1.);
    float result=geo;
    return result;
}

vec2 sdf(vec3 p){
    float result=opU(abs(fire(p)),-(length(p)-100.));
    float objType=1.;
    return vec2(result,objType);
}

vec4 rayMarch(vec3 eye,vec3 ray){
    float depth=0.;
    float strength=0.;
    float eps=.02;
    vec3 pos=eye;
    for(int i=0;i<64;i++){
        pos+=depth*ray;
        float dist=sdf(pos).x;
        depth=dist+eps;
        if(dist>0.){
            strength=float(i)/64.;
        }
    }
    return vec4(pos,strength);
}

void main(){
    vec2 p=centerUv(vUv,uResolution);
    p=p*vec2(1.6,-1);
    
    vec3 ro=vec3(0.,-2.,4.);
    vec3 ta=vec3(0.,-2.5,-1.5);
    float fl=1.25;
    vec3 rd=getRayDirection(p,ro,ta,fl);
    
    vec3 color=vec3(0.);
    
    vec4 result=rayMarch(ro,rd);
    
    float strength=pow(result.w*2.,4.);
    vec3 ellipse=vec3(strength);
    color=ellipse;
    
    gl_FragColor=vec4(color,1.);
}
复制代码

centerUv.glsl

vec2 centerUv(vec2 uv,vec2 resolution){
    uv=2.*uv-1.;
    float aspect=resolution.x/resolution.y;
    uv.x*=aspect;
    return uv;
}

#pragma glslify:export(centerUv);
复制代码

getRayDirection.glsl

#pragma glslify:setCamera=require(./setCamera)

vec3 getRayDirection(vec2 p,vec3 ro,vec3 ta,float fl){
    mat3 ca=setCamera(ro,ta,0.);
    vec3 rd=ca*normalize(vec3(p,fl));
    return rd;
}

#pragma glslify:export(getRayDirection)
复制代码

setCamera.glsl

mat3 setCamera(in vec3 ro,in vec3 ta,float cr)
{
    vec3 cw=normalize(ta-ro);
    vec3 cp=vec3(sin(cr),cos(cr),0.);
    vec3 cu=normalize(cross(cw,cp));
    vec3 cv=(cross(cu,cw));
    return mat3(cu,cv,cw);
}

#pragma glslify:export(setCamera)
复制代码

R0RM7Q.png

用噪声生成火花

接下来就对这个椭圆应用上噪声(这里选了传统噪声,为了更好看的外观,也可以选择其他的噪声)

float fire(vec3 p){
    vec3 p2=p*vec3(1.,.5,1.)+vec3(0.,1.,0.);
    float geo=sdSphere(p2,1.);
    // float result=geo;
    float displacement=uTime*uVelocity;
    vec3 displacementY=vec3(.0,displacement,.0);
    float noise=(cnoise(p+displacementY))*p.y*.4;
    float result=geo+noise;
    return result;
}
复制代码

R0fRFH.gif

莫名感觉像黑魂3里的芙莉德修女的黑焰,尽管这样也很cool,我们还是给它加上颜色,让它更像现实中的火花

给火花加上颜色

将颜色通过mix函数混合起来(强度是光线位置的y轴),和之前的颜色相乘即可

void main(){
    ...
    
    float fireBody=result.y/64.;
    vec3 mixColor=mix(uColor1,uColor2,fireBody);
    color*=mixColor;
    
    gl_FragColor=vec4(color,1.);
}
复制代码

项目地址

Ray Marching Fire

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