shader编程-三维场景下SDF建模,对模型进行扭曲弯曲裁剪掏空操作(WebGL-Shader开发基础12)

Posted 点燃火柴

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了shader编程-三维场景下SDF建模,对模型进行扭曲弯曲裁剪掏空操作(WebGL-Shader开发基础12)相关的知识,希望对你有一定的参考价值。

对模型进行扭曲、弯曲、裁剪、掏空操作

1. demo效果




如上图所示,第一张是对方形圆柱进行扭曲操作的效果图,第二张图是对扁平立方体面进行弯曲操作的效果图,第三张图是从内到外依次是原物体,裁剪后的物体,裁剪后掏空物体的效果,从左到右依次对圆柱、球体、甜圈圈进行同样变换的效果

2. 实现要点

先回顾一下之前学习的SDF建模相关的一些操作,首先学习了基本变换旋转、缩放、平移,之后学习了通过布尔运算(交集、并集、差集)组合模型 ,进而拓展了平滑布尔运算组合模型,今天解锁一点点新的技能,对模型进行扭曲、弯曲、裁剪、掏空操作

2.1 模型扭曲

通过前面的demo效果展示知道,我们首先绘制了一个长条状的立方体,然后又绘制了一个以同样立方体扭曲后的物体,实现的核心思想就是变换用来绘制扭曲立方体的坐标,即依据y分量的变化使x分量和z分量转圈圈,具体代码如下

vec3 opTwistY( in vec3 p ,float k)


  float c = cos(k*p.y);
  float s = sin(k*p.y);
  mat2  m = mat2(c,-s,s,c);
  p.xz *=m;
  return p;

如果你想物体绕z轴或x轴扭曲,两种办法,一是先按y轴扭曲然后将物体旋转,二是将上面的函数中的分量替换为对应的坐标轴

扭曲的坐标处理完接着就是像之前一样绘制图形,为了方便使用我们将绘制过程封装成了一个函数,具体如下

vec2 twistBox (vec4 pos)

  //绘制原立方体
  pos.x += 2.5; 
  float box1 = sdBox(pos.xyz,vec3(0.4,1.2,0.4),0.06);//方块
  vec2 mBox1 = vec2(box1,1.0);

  //绘制扭曲立方体
  pos.x -= 5.0; 
  pos.xyz=opTwistY(pos.xyz,3.0);//扭曲
  float box2 = sdBox(pos.xyz,vec3(0.4,1.2,0.4),0.06);//方块
  vec2 mBox2 = vec2(box2,1.0);

  vec2 res = opU(mBox1,mBox2);

  return res;

调用过程如下

vec2 res =  vec2(p.y,0.0);//地面

vec3 pos = p-vec3(0,2,5);//确定模型的中心
vec4 oriPos = vec4(pos,1.0);//转为其次坐标

//扭曲
vec2 twistBox = twistBox(oriPos);

res = opU(res,twistBox);//扭曲立方体

2.2 模型弯曲

弯曲也是同样的思想,通过改变绘制弯曲模型的坐标来实现,返回弯曲坐标的函数如下

vec3 opCheapBend(in vec3 p ,float k)

  float c = cos(k*p.x);
  float s = sin(k*p.x);
  mat2  m = mat2(c,-s,s,c);
  vec3  q = vec3(m*p.xy,p.z);
  return q;

像上一次一样,使用处理好的坐标绘制图形即可,这次也将绘制过程封装成了一个函数,具体如下

vec2 cheapBendBox (vec4 pos)

  //绘制原立方体面
  pos.x += 2.5; 
  float box1 = sdBox(pos.xyz,vec3(1.0,0.2,0.6),0.06);//方块
  vec2 mBox1 = vec2(box1,1.0);

  //绘制弯曲立方体面
  pos.x -= 5.0; 
  pos.xyz=opCheapBend(pos.xyz,0.5);//弯曲
  float box2 = sdBox(pos.xyz,vec3(1.0,0.2,0.6),0.06);//方块
  vec2 mBox2 = vec2(box2,1.0);

  vec2 res = opU(mBox1,mBox2);

  return res;

调用过程如下

vec2 res =  vec2(p.y,0.0);//地面

vec3 pos = p-vec3(0,2,5);//确定模型的中心
vec4 oriPos = vec4(pos,1.0);//转为其次坐标

//扭曲
vec2 twistBox = twistBox(oriPos);

//弯曲
vec2 cheapBendBox = cheapBendBox(oriPos);
//res = opU(res,twistBox);//扭曲立方体
res = opU(res,cheapBendBox); //弯曲立方体

2.3 模型裁剪与掏空

2.3.1 球体裁剪与掏空

掏空函数

//掏空
float opOnion(float sdf, in float thickness )

  return abs(sdf)-thickness;

绘制过程是,我们首先绘制了一个完整的球体,然后绘制了一个裁剪的球体,最后绘制一个掏空且裁剪的球体,之所以也裁剪是因为不裁剪的画我们看不到内部结构,具体如下

vec2 onionSphere (vec4 pos)

  //绘制球体
  vec4 pos1 = pos;
  pos1.z -= 6.0; 
  float sphere1 = sdSphere(pos1.xyz,0.6);
  vec2 mSphere1 = vec2(sphere1,2.0);

  //绘制裁剪球体
  vec4 pos2 = pos;
  pos2.z -= 2.5; 
  float sphere2 = sdSphere(pos2.xyz,0.6);
  sphere2 = max( sphere2, pos2.y );//裁剪

  vec2 mSphere2 = vec2(sphere2,2.0);

  //绘制裁剪掏空球体
  vec4 pos3 = pos;
 
  float sphere3 = sdSphere(pos3.xyz,0.6);

  sphere3 = opOnion(sphere3,0.01);//掏空
  sphere3 = max( sphere3, pos3.y );//裁剪
  vec2 mSphere3 = vec2(sphere3,2.0);

  vec2 res = opU(mSphere1,mSphere2);
  res = opU(res,mSphere3);

  return res;

关于裁剪,不知你有没有联想到,这里的裁剪效果是裁掉了y轴大于0 的部分,如果想裁掉x轴或z上的大于0的部分,只需把max( sphere3, pos3.y );//裁剪此处的分量y替换,如果你想要留下y轴上部分,即demo中裁掉和留下的部分互换,那么在y分量前添加负号即可,max( sphere3, -pos3.y );//裁剪,其他轴中的裁剪同理

2.3.2 圆柱裁剪与掏空

圆柱的实现与球体的思路一样,只不过把球体换成圆柱,如下

vec2 onionCylinder (vec4 pos)

  //绘制圆柱
  vec4 pos1 = pos;
  pos1.z -= 6.0; 
  float cylinder1 = sdCylinder(pos1.xyz,0.4,0.6);
  vec2 mCylinder1 = vec2(cylinder1,1.0);

  //绘制裁剪圆柱
  vec4 pos2 = pos;
  pos2.z -= 2.5; 
  float cylinder2 = sdCylinder(pos2.xyz,0.4,0.6);
  cylinder2 = max( cylinder2, pos2.y );//裁剪

  vec2 mCylinder2 = vec2(cylinder2,1.0);

  //绘制裁剪掏空圆柱
  vec4 pos3 = pos;

  float cylinder3 = sdCylinder(pos3.xyz,0.4,0.6);

  cylinder3 = opOnion(cylinder3,0.01);//掏空
  cylinder3 = max( cylinder3, pos3.y );//裁剪
  vec2 mCylinder3 = vec2(cylinder3,1.0);

  vec2 res = opU(mCylinder1,mCylinder2);
  res = opU(res,mCylinder3);

  return res;

2.3.3 甜圈圈裁剪与掏空

甜圈圈裁剪与掏空也是同样的思路,绘制过程如下

vec2 onionTorus (vec4 pos)

  //绘制甜圈圈
  vec4 pos1 = pos;
  pos1.z -= 6.0; 
  float torus1 = sdTorus(pos1.xyz,vec2(0.6,0.2));
  vec2 mTorus1 = vec2(torus1,3.0);

  //绘制裁剪甜圈圈
  vec4 pos2 = pos;
  pos2.z -= 2.5; 
  float torus2 = sdTorus(pos2.xyz,vec2(0.6,0.2));
  torus2 = max( torus2, pos2.y );//裁剪

  vec2 mTorus2 = vec2(torus2,3.0);

  //绘制裁剪掏空甜圈圈
  vec4 pos3 = pos;

  float torus3 = sdTorus(pos3.xyz,vec2(0.6,0.2));

  torus3 = opOnion(torus3,0.01);//掏空
  torus3 = max( torus3, pos3.y );//裁剪
  vec2 mTorus3 = vec2(torus3,3.0);

  vec2 res = opU(mTorus1,mTorus2);
  res = opU(res,mTorus3);

  return res;

3. demo代码

继续,可直接跑起来的代码

<body>
  <div id="container"></div>
  <script src="http://www.yanhuangxueyuan.com/versions/threejsR92/build/three.js"></script>
  <script>
    var container;
    var camera, scene, renderer;
    var uniforms;
    var vertexShader = `
      void main() 
        gl_Position = vec4( position, 1.0 );
       
    `
    var fragmentShader = `
    #ifdef GL_ES
    precision mediump float;
    #endif
    uniform float u_time;
    uniform vec2 u_mouse;
    uniform vec2 u_resolution;

    const int MAX_STEPS = 100;//最大步进步数
    const float MAX_DIST = 100.0;//最大步进距离
    const float SURF_DIST = 0.01;//相交检测临近表面距离

    //绕z轴旋转矩阵
    mat4 rotZ(float a) 
      return mat4(cos(a),-sin(a),0.0,0.0,
                  sin(a),cos(a),0.0,0.0,
                  0.0,0.0,1.0,0.0,
                  0.0,0.0,0.0,1.0
                  );
    
    
    //绕x轴旋转矩阵
    mat4 rotX(float a) 
      return mat4(1.0,0.0,0.0,0.0,
                  0.0,cos(a),-sin(a),0.0,
                  0.0,sin(a),cos(a),0.0,
                  0.0,0.0,0.0,1.0
                );
    
    
    //绕y轴旋转矩阵
    mat4 rotY(float a) 
      return mat4(cos(a),0.0,sin(a),0.0,
                  0.0,1.0,0.0,0.0,
                  -sin(a),0.0,cos(a),0.0,
                  0.0,0.0,0.0,1.0
                );
     

    //平滑交集
    float opSmoothI( float d1, float d2, float k )
    
      float h = max(k-abs(d1-d2),0.0);
      return max(d1, d2) + h*h*0.25/k;
    

    //平滑并集
    float opSmoothU( float d1, float d2, float k )
    
      float h = max(k-abs(d1-d2),0.0);
      return min(d1, d2) - h*h*0.25/k;
    

    //平滑差集
    float opSmoothS( float d1, float d2, float k )
    
      float h = max(k-abs(-d1-d2),0.0);
      return max(-d1, d2) + h*h*0.25/k;
    

    //掏空
    float opOnion(float sdf, in float thickness )
    
      return abs(sdf)-thickness;
    

    //并集
    vec2 opU( vec2 d1, vec2 d2 )
    
      return (d1.x<d2.x) ? d1 : d2;
    


    //球体
    float sdSphere( vec3 p, float s )
    
      return length(p)-s;
    

    //立方体
    float sdBox( vec3 p, vec3 b,float rad )
    
      vec3 d = abs(p) - b;
      return min(max(d.x,max(d.y,d.z)),0.0) + length(max(d,0.0)) - rad;
    

    //圆柱
    float sdCylinder( vec3 p, float h, float r )
    
      vec2 d = abs(vec2(length(p.xz),p.y)) - vec2(r,h);
      return min(max(d.x,d.y),0.0) + length(max(d,0.0));
    

    //甜圈圈
    float sdTorus( vec3 p, vec2 t )
    
      vec2 q = vec2(length(p.xz)-t.x,p.y);
      return length(q)-t.y;
    

    vec3 opTwistY( in vec3 p ,float k)
    

      float c = cos(k*p.y);
      float s = sin(k*p.y);
      mat2  m = mat2(c,-s,s,c);
      p.xz *=m;
      return p;
    

    vec3 opCheapBend(in vec3 p ,float k)
    

      float c = cos(k*p.x);
      float s = sin(k*p.x);
      mat2  m = mat2(c,-s,s,c);
      vec3  q = vec3(m*p.xy,p.z);
      return q;
    


    vec2 twistBox (vec4 pos)

      //绘制原立方体
      pos.x += 2.5; 
      float box1 = sdBox(pos.xyz,vec3(0.4,1.2,0.4),0.06);//方块
      vec2 mBox1 = vec2(box1,1.0);

      //绘制扭曲立方体
      pos.x -= 5.0; 
      pos.xyz=opTwistY(pos.xyz,3.0);//扭曲
      float box2 = sdBox(pos.xyz,vec3(0.4,1.2,0.4),0.06);//方块
      vec2 mBox2 = vec2(box2,1.0);

      vec2 res = opU(mBox1,mBox2);

      return res;
    

    vec2 onionCylinder (vec4 pos)

      //绘制圆柱
      vec4 pos1 = pos;
      pos1.z -= 6.0; 
      float cylinder1 = sdCylinder(pos1.xyz,0.4,0.6);
      vec2 mCylinder1 = vec2(cylinder1,1.0);

      //绘制裁剪圆柱
      vec4 pos2 = pos;
      pos2.z -= 2.5; 
      float cylinder2 = sdCylinder(pos2.xyz,0.4,0.6);
      cylinder2 = max( cylinder2, pos2.y );//裁剪

      vec2 mCylinder2 = vec2(cylinder2,1.0);

      //绘制裁剪掏空圆柱
      vec4 pos3 = pos;

      float cylinder3 = sdCylinder(pos3.xyz,0.4,0.6);

      cylinder3 = opOnion(cylinder3,0.01);//掏空
      cylinder3 = max( cylinder3, pos3.y );//裁剪
      vec2 mCylinder3 = vec2(cylinder3,1.0);

      vec2 res = opU(mCylinder1,mCylinder2);
      res = opU(res,mCylinder3);

      return res;
    
    vec2 onionSphere (vec4 pos)

      //绘制球体
      vec4 pos1 = pos;
      pos1.z -= 6.0; 
      float sphere1 = sdSphere(pos1.xyz,0.6);
      vec2 mSphere1 = vec2(sphere1,2.0);

      //绘制裁剪球体
      vec4 pos2 = pos;
      pos2.z -= 2.5; 
      float sphere2 = sdSphere(pos2.xyz,0.6);
      sphere2 = max( sphere2, pos2.y );//裁剪

      vec2 mSphere2 = vec2(sphere2,2.0);

      //绘制裁剪掏空球体
      vec4 pos3 = pos;
     
      float sphere3 = sdSphere(pos3.xyz,0.6);
 
      sphere3 = opOnion(sphere3,0.01);//掏空
      sphere3 = max( sphere3, pos3.y );//裁剪
      vec2 mSphere3 = vec2(sphere3,2.0);

      vec2 res = opU(mSphere1,mSphere2);
      res = opU(res,mSphere3);

      return res;
    

    vec2 onionTorus (vec4 pos)

      //绘制甜圈圈
      vec4 pos1 = pos;
      pos1.z -= 6.0; 
      float torus1 = sdTorus(pos1.xyz,vec2(0.6,0.2));
      vec2 mTorus1 = vec2(torus1,3.0);

      //绘制裁剪甜圈圈
      vec4 pos2 = pos;
      pos2.z -= 2.5; 
      float torus2 = sdTorus(pos2.xyz,vec2(0.6,0.2));
      torus2 = max( torus2, pos2.y );//裁剪

      vec2 mTorus2 = vec2(torus2,3.0);

      //绘制裁剪掏空甜圈圈
      vec4 pos3 = pos;

      float torus3 = sdTorus(pos3.xyz,vec2(0.6,0.2));

      torus3 = opOnion(torus3,0.01);//掏空
      torus3 = max( torus3, pos3.y );//裁剪
      vec2 mTorus3 = vec2(torus3,3.0);

      vec2 res = opU(mTorus1,mTorus2);
      res = opU(res,mTorus3);

      return res;
    

    vec2 cheapBendBox (vec4 pos)

      //绘制原立方体面
      pos.x += 2.5; 
      float box1 = sdBox(pos.xyz,vec3(1.0,0.2,0.6),0.06);//方块
      vec2 mBox1 = vec2(box1,1.0);

      //绘制弯曲立方体面
      pos.x -= 5.0; 
      pos.xyz=opCheapBend(pos.xyz,0.5);//弯曲
      float box2 = sdBox(pos.xyz,vec3(1.0,0.2,0.6),0.06);//方块
      vec2 mBox2 = vec2(box2,1.0);

      vec2 res = opU(mBox1,mBox2);

      return res;
    

    vec2 getDistandMaterial(vec3 p)

      vec2 res =  vec2(p.y,0.0);//地面
 
      vec3 pos = p-vec3(0,2,5);//确定模型的中心
      vec4 oriPos = vec4(pos,1.0);//转为其次坐标
 
      //扭曲
      vec2 twistBox = twistBox(oriPos);

      //弯曲
      vec2 cheapBendBox = cheapBendBox(oriPos);


      //裁剪掏空
      vec2 onionSphere = onionSphere(oriPos);

      vec2 onionCylinder = onionCylinder(oriPos+vec4(2.0,0.0,0.0,1.0));

      vec2 onionTorus = onionTorus(oriPos-vec4(2.0,0.0,0.0,1.0));

   
      //res = opU(res,twistBox);//扭曲立方体
      //res = opU(res,cheapBendBox); //弯曲立方体
      res = opU(res,onionSphere);//裁剪掏空球体
      res = opU(res,onionCylinder);//裁剪掏空圆柱
      res = opU(res,onionTorus);//裁剪掏空甜圈圈

      return res;
    

    vec2 rayMarch(vec3 rayStart, vec3 rayDirection) 
      float depth=0.;
      float material=0.;
      for(int i=0; i<MAX_STEPS; i++) 
        vec3 p = rayStart + rayDirection*depth;//上一次步进结束后的坐标也就是这一次步进出发点

        vec2 dm = getDistandMaterial(p);
        float dist = dm.x;//获取当前步进出发点与物体相交时距离
        material = dm.y;
        depth += dist; //步进长度累加

        if(depth>MAX_DIST || dist<SURF_DIST) break;//步进距离大于最大步进距离或与物体表面距离小于最小表面距离(光线进入物体)停止前进
      
      return vec2(depth,material);
    

    vec3 getNormal(vec3 p)
      return normalize(vec3(
        getDistandMaterial(vec3(p.x + SURF_DIST, p.y, p.z)).x - getDistandMaterial(vec3(p.x - SURF_DIST, p.y, p.z)).x,
        getDistandMaterial(vec3(p.x, p.y + SURF_DIST, p.z)).x - getDistandMaterial(vec3(p.x, p.y - SURF_DIST, p.z)).x,
        getDistandMaterial(vec3(p.x, p.y, p.z  + SURF_DIST)).x - getDistandMaterial(vec3(p.x, p.y, p.z - SURF_DIST)).x
      ));
    


    //Blinn-Phong模型光照计算
    vec3 calcBlinnPhongLight( vec3 materialColor, vec3 p, vec3 ro) 

      vec3 lightPos = vec3(5.0 * sin(u_time), 20.0, 10.0*cos(u_time)-18.);//光源坐标

      //计算环境光
      float k_a = 0.3;//环境光反射系数
      vec3 ambientLight = 0.6 * vec3(1.0, 1.0, 1.0);
      vec3 ambient = k_a*ambientLight;
      
      vec3 N = getNormal(p); //法线
      vec3 L = normalize(lightPos - p); //光照方向
      vec3 V = normalize(ro - p); //视线
      vec3 H = normalize(V+L); //半程向量

      float r = length(lightPos - p);


      //计算漫反射光
      float k_d = 0.6;//漫反射系数
      float dotLN = clamp(dot(L, N),0.0,1.0);//点乘,并将结果限定在0~1
      vec3 diffuse = k_d * (materialColor/r*r) * dotLN;


      //计算高光反射光
      float k_s = 0.8;//镜面反射系数
      float shininess = 160.0;
      vec3 specularColor = vec3(1.0, 1.0, 1.0);
      vec3 specular = k_s * (specularColor/r*r)* pow(clamp(dot(N, H), 0.0, 1.0), shininess);//计算高光
  
      
      //计算阴影
      vec2 res = rayMarch(p + N*SURF_DIST*2.0,L); 
      if(res.x<length(lightPos-p)-0.001)
        diffuse*=0.1;
      
        
      //颜色 =  环境光 + 漫反射光 + 镜面反射光
      return ambient +diffuse + specular;
    

    void main( void ) 

      //窗口坐标调整为[-1,1],坐标原点在屏幕中心
      vec2 st = (gl_FragCoord.xy * 2. - u_resolution) / u_resolution.y;


      vec3 ro = vec3(0.0,4.0,0.0);//视点
      vec3 rd = normalize(vec3(st.x,st.y,1.0));//视线方向

      vec2 res = rayMarch(ro,rd);//反向光线追踪求交点距离与材质ID

      float d = res.x;//物体与视点的距离
      float m = res.y;//材质ID
  
      vec3 p = ro + rd * d;

      vec3 materialColor = vec3(1.0, 0.0, 1.0);//默认材质色,使用差集计算出来的内壁会使用该色填充
      
      
      //为不同物体设置不同的材质颜色
      if(m==0.0)
        materialColor = vec3(.2, 0.0, 0.0);
      
      if(m==1.0)
        materialColor = vec3(.2, 0.0, 1.0);
      
      if(m==2.0)
        materialColor = vec3(.7, 0.2, 0.0);
      
      if(m==3.0)
        materialColor = vec3(.8, .9, 0.0);
      

      vec3 color = vec3(1.0,1.0,1.0);

      //使用Blinn-Phong模型计算光照
      color *= calcBlinnPhongLight( materialColor, p, ro);

      gl_FragColor = vec4(color, 1.0);

    
    `

    init();
    animate();

    function init() 
      container = document.getElementById('container');

      camera = new THREE.Camera();
      camera.position.z = 1;

      scene = new THREE.Scene();

      var geometry = new THREE.PlaneBufferGeometry(2, 2);

      uniforms = 
        u_time: 
          type: "f",
          value: 1.0
        ,
        u_resolution: 
          type: "v2",
          value: new THREE.Vector2()
        ,
        u_mouse: 
          type: "v2",
          value: new THREE.Vector2()
        
      ;

      var material = new THREE.ShaderMaterial(
        uniforms: uniforms,
        vertexShader: vertexShader,
        fragmentShader: fragmentShader
      );

      var mesh = new THREE.Mesh(geometry, material);
      scene.add(mesh);

      renderer = new THREE.WebGLRenderer();
      //renderer.setPixelRatio(window.devicePixelRatio);

      container.appendChild(renderer.domElement);

      onWindowResize();
      window.addEventListener('resize', onWindowResize, false);

      document.onmousemove = function (e) 
        uniforms.u_mouse.value.x = e.pageX
        uniforms.u_mouse.value.y = e.pageY
      
    

    function onWindowResize(event) 
      renderer.setSize(800, 800);
      uniforms.u_resolution.value.x = renderer.domElement.width;
      uniforms.u_resolution.value.y = renderer.domElement.height;
    

    function animate() 
      requestAnimationFrame(animate);
      render();
    

    function render() 
      uniforms.u_time.value += 0.02;
      renderer.render(scene, camera);
    
  </script>
</body>

以上是关于shader编程-三维场景下SDF建模,对模型进行扭曲弯曲裁剪掏空操作(WebGL-Shader开发基础12)的主要内容,如果未能解决你的问题,请参考以下文章

shader编程-三维场景下SDF建模,对模型进行扭曲弯曲裁剪掏空操作(WebGL-Shader开发基础12)

shader编程-三维场景下SDF建模,对模型进行扭曲弯曲裁剪掏空操作(WebGL-Shader开发基础12)

shader编程-三维场景下SDF建模,平滑交集平滑并集平滑差集(WebGL-Shader开发基础11)

shader编程-三维场景下SDF建模,平滑交集平滑并集平滑差集(WebGL-Shader开发基础11)

shader编程-三维场景下SDF建模,平滑交集平滑并集平滑差集(WebGL-Shader开发基础11)

shader编程-三维场景下SDF建模,平滑交集平滑并集平滑差集(WebGL-Shader开发基础11)