Houdini湖边小屋-屋顶细分详细过程记录

蔚落 2023-09-30 08:43 14阅读 0赞

b站UP主七里雪凝的湖边小屋教程——P3/P4[【Houdini】萌新的《湖边小屋》教程拆解与实现，殊途同归！\_哔哩哔哩\_bilibili][Houdini_bilibili]

**目录**

内容概括

详细步骤

1 \[Facet节点\]让每个ceiling面片拥有自己的points

2 \[Attribute Wrangle节点\]定义一些需要用到的属性

3 \[Attribute Wrangle节点\]划分branch面

3 \[Attribute Wrangle节点\]划分trunk面

4 \[Attribute Wrangle节点\]调整branch的trunk面

5 \[Group Delete节点\]删除不用的group

6 \[Attribute Wrangle节点\]划分每个roof面的level高度

用到的节点

1.facet节点

用到的VEX function

1.expandprimgroup

2.primpoints

3.getbbox

2.itoa

3.addpoint

4.set

5.setprimvertex

--------------------

### 内容概括 ###

把ceiling组的面片正确划分，为拉伸屋顶做准备。

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_13_color_FFFFFF_t_70_g_se_x_16][]

### 详细步骤 ###

#### 1 \[Facet节点\]让每个ceiling面片拥有自己的points ####

用到了**facet节点**

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_11_color_FFFFFF_t_70_g_se_x_16][]

#### 2 \[Attribute Wrangle节点\]定义一些需要用到的属性 ####

主要用到了**Attribute Wrangle节点**。

教程中形象的用主干trunk和分支branch表示ceiling的面片地位，设定属性，与**attribute create节点**作用相同**，**可以直接在attribute wrangle里用 **i@...=...** 来设定属性并赋予初始值。

初值设置为-1是为了与自动初值0分开来。

关于 Houdini中@定义属性的问题可以看看这篇文章：[Houdini定义属性方式-CSDN][Houdini_-CSDN]

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_15_color_FFFFFF_t_70_g_se_x_16][]

#### 3 \[Attribute Wrangle节点\]划分branch面 ####

这一步 **Run Over** 选择 **Detail(only once)** 让代码仅运行一次，以下是完整代码：

int pts[];
    vector q0, q1, p1, p2, dir, tan;
    vector src_minpos, src_maxpos, dst_minpos, dst_maxpos;
    int ptnum1, ptnum2, new_prim, tri_prim1, tri_prim2;
    int join_head, join_tail;
    float width;
    
    int prims[] = expandprimgroup(0, "ceiling"); //get all the prims
    foreach(int main_prim; prims) { //use main_prim to get every prim_number as branch-prim
      pts = primpoints(0, main_prim); //get all points of main_prim
      getbbox(0, itoa(main_prim), src_minpos, src_maxpos); //get bounding box max&min, returns vectors
      foreach(int primnum; prims) {
        getbbox(0, itoa(primnum), dst_minpos, dst_maxpos); // get a prim as trunk-prim
        if(abs(src_minpos.y - dst_minpos.y) > 0.01) continue; // two prims should be in the same "y"
        q0 = point(0, "P", pts[0]);
        q1 = point(0, "P", pts[1]); //get two near points
        if(abs(src_minpos.z - dst_maxpos.z) < 0.01 || abs(src_maxpos.z - dst_minpos.z) < 0.01) {
          if((dst_minpos.x < src_minpos.x + 0.01) && (dst_maxpos.x + 0.01 > src_maxpos.x)){
            p1 = set((src_minpos.x + src_maxpos.x)/2.0, src_minpos.y, src_minpos.z);
            p2 = set((src_minpos.x + src_maxpos.x)/2.0, src_maxpos.y, src_maxpos.z);
            dir = abs(src_minpos.z - dst_maxpos.z) < 0.01 ? {0,0,-1} : {0,0,1};
            ptnum1 = addpoint(0, p1);
            ptnum2 = addpoint(0, p2);
            p1 = p1.zyx; //change z->x x->z
            p2 = p2.zyx;
            q0 = q0.zyx;
            q1 = q1.zyx;
          }else continue; // the primnum-prim can not be a trunk
          }else if (abs(src_minpos.x - dst_maxpos.x) < 0.01 || abs(src_maxpos.x - dst_minpos.x) < 0.01){
            if(dst_minpos.z - 0.01 < src_minpos.z && dst_maxpos.z + 0.01 > src_maxpos.z){
              p1 = set(src_minpos.x, src_minpos.y, (src_minpos.z + src_maxpos.z)/2);
              p2 = set(src_maxpos.x, src_maxpos.y, (src_minpos.z + src_maxpos.z)/2);
              dir = abs(src_minpos.x - dst_maxpos.x) < 0.01 ? {-1,0,0} : {1,0,0};
              ptnum1 = addpoint(0, p1);
              ptnum2 = addpoint(0, p2);
              }else continue;
            }else continue;
    
          int flag = abs(q0.x - q1.x) < 0.01;//flag =1,lineq0q1 is vertical to linep1p2
          if(abs(q0.x - p1.x) < 0.01){ //q0 and p1 are on the same "x"
          setprimvertex(0, main_prim, flag, ptnum1);
          setprimvertex(0, main_prim, flag + 1, ptnum2);
          new_prim = addprim(0, "poly", pts[flag], pts[flag + 1], ptnum2, ptnum1);
          tri_prim1 = addprim(0, "poly", pts[flag - 1], pts[flag], ptnum1);
          tri_prim2 = addprim(0, "poly", pts[flag + 1], pts[flag + 2], ptnum2);
          }else{ //q0 and p2 are on the same "x"
          setprimvertex(0, main_prim, flag + 0, ptnum2);
          setprimvertex(0, main_prim, flag + 1, ptnum1);
          new_prim = addprim(0, "poly", pts[flag], pts[flag + 1], ptnum1, ptnum2);
          tri_prim1 = addprim(0, "poly", pts[flag-1], pts[flag], ptnum2);
          tri_prim2 = addprim(0, "poly", pts[flag + 1], pts[flag + 2], ptnum1);
        }
          //tri_prim1 attributes
          setprimgroup(0, "triangle", tri_prim1, 1, "set");
          setprimattrib(0, "join_head", tri_prim1, -1, "set"); //initialvalue need to be set as "-1"
          setprimattrib(0, "join_tail", tri_prim1, -1, "set");
          setprimattrib(0, "trunk", tri_prim1, primnum, "set");
          setprimattrib(0, "heading", tri_prim1, dir, "set");
          setprimattrib(0, "twin", tri_prim1, -1, "set");
         
          //tri_prim2 attributes
          setprimgroup(0, "triangle", tri_prim2, 1, "set");
          setprimattrib(0, "join_head", tri_prim2, -1, "set");
          setprimattrib(0, "join_tail", tri_prim2, -1, "set");
          setprimattrib(0, "trunk", tri_prim2, primnum, "set");
          setprimattrib(0, "heading", tri_prim2, dir, "set");
          setprimattrib(0, "twin", tri_prim2, -1, "set");
          
          //set join_head and join_tail value
          join_head = dir.x + dir.z > 0.01 ? ptnum2 : ptnum1;
          join_tail = dir.x + dir.z > 0.01 ? ptnum1 : ptnum2;
          tan = point(0, "P", pts[flag - 1]) - point(0, "P", pts[flag]);
          width = length(tan)/2;
          
          //new_prim attributes
          setprimattrib(0, "N", new_prim, {0,1,0}, "set"); //normal
          setprimgroup(0, "roof", new_prim, 1, "set");
          setprimattrib(0, "twin", new_prim, main_prim, "set");
          setprimattrib(0, "trunk", new_prim, primnum, "set");
          setprimattrib(0, "dir", new_prim, dir, "set");
          setprimattrib(0, "join_head", new_prim, join_head, "set");
          setprimattrib(0, "join_tail", new_prim, -1, "set");
          setprimattrib(0, "width", new_prim, width, "set");
          
          //old prim main_prim attributes
          setprimgroup(0, "ceiling", main_prim, 0, "set"); //remove from group"ceiling"
          setprimgroup(0, "roof", main_prim, 1, "set"); // add to the newgroup "roof"
          setprimattrib(0, "twin", main_prim, new_prim, "set");
          setprimattrib(0, "trunk", main_prim, primnum, "set");
          setprimattrib(0, "dir", main_prim, dir, "set");
          setprimattrib(0, "join_tail", main_prim, join_tail, "set");
          setprimattrib(0, "width", main_prim, width, "set");
    
          setprimattrib(0, "branch", primnum, main_prim, "append");
          setprimattrib(0, "branch", primnum, new_prim, "append");
          break;
        }
      }

**每一步的详细理解**

//定义变量
    //其中，以下所有涉及到判断的在＞左边和＜右边都会有0.01，来使判断更加精确
    int pts[];
    vector q0, q1, p1, p2, dir, tan;
    vector src_minpos, src_maxpos, dst_minpos, dst_maxpos;//编号src在下面代表着branch的面上点，dst代表着trunk的面上点
    int ptnum1, ptnum2, new_prim, tri_prim1, tri_prim2;
    int join_head, join_tail;
    float width;
    
    int prims[] = expandprimgroup(0, "ceiling"); //得到group“ceiling”里所有面的面号
    foreach(int main_prim; prims) { //用main_prim取循环提取prims数组中的每个面号
      pts = primpoints(0, main_prim); //得到面号为main_prim的面上的所有点号
      getbbox(0, itoa(main_prim), src_minpos, src_maxpos); //得到这个面的bounding box的最小点和最大点的坐标，点的类型是vector，这里用到itoa是把整型int转换成string为了拟合getbbox这个函数的用法规则
      foreach(int primnum; prims) {
        getbbox(0, itoa(primnum), dst_minpos, dst_maxpos);
        if(abs(src_minpos.y - dst_minpos.y) > 0.01) continue; //src和dst面至少要在同一个高度，也就是y要相同，如果不同 则跳出这层循环，继续找与src面匹配的dst面
        q0 = point(0, "P", pts[0]);
        q1 = point(0, "P", pts[1]); //这里的pts就是上面拿到的main_prim面上的点数组，得到点好为0和1的相邻点
        //以下是判断部分
        if(abs(src_minpos.z - dst_maxpos.z) < 0.01 || abs(src_maxpos.z - dst_minpos.z) < 0.01) {两个面是左右的关系
          if((dst_minpos.x < src_minpos.x + 0.01) && (dst_maxpos.x + 0.01 > src_maxpos.x)){
            p1 = set((src_minpos.x + src_maxpos.x)/2.0, src_minpos.y, src_minpos.z);
            p2 = set((src_minpos.x + src_maxpos.x)/2.0, src_maxpos.y, src_maxpos.z);
            dir = abs(src_minpos.z - dst_maxpos.z) < 0.01 ? {0,0,-1} : {0,0,1};
            ptnum1 = addpoint(0, p1);
            ptnum2 = addpoint(0, p2); //注意，set只是创建了vector,还需要addpoint来创建点
            p1 = p1.zyx; //change z->x x->z
            p2 = p2.zyx;
            q0 = q0.zyx;
            q1 = q1.zyx;
          }else continue; //说明trunk面在x轴方向上无法把branch面包含住，因此跳出这次循环，继续找下一个trunk面
          }else if (abs(src_minpos.x - dst_maxpos.x) < 0.01 || abs(src_maxpos.x - dst_minpos.x) < 0.01){
            if(dst_minpos.z - 0.01 < src_minpos.z && dst_maxpos.z + 0.01 > src_maxpos.z){
              p1 = set(src_minpos.x, src_minpos.y, (src_minpos.z + src_maxpos.z)/2);
              p2 = set(src_maxpos.x, src_maxpos.y, (src_minpos.z + src_maxpos.z)/2);
              dir = abs(src_minpos.x - dst_maxpos.x) < 0.01 ? {-1,0,0} : {1,0,0};
              ptnum1 = addpoint(0, p1);
              ptnum2 = addpoint(0, p2);
              }else continue;
            }else continue;//这个else是两个面的位置无论在左右还是上下方向上都不共边，因此两个面处于独立关系，重新找trunk面
    
          int flag = abs(q0.x - q1.x) < 0.01;//判断成立，则flag=1，说明线q0q1⊥p1p2 反之则q0q1∥p1p2
          if(abs(q0.x - p1.x) < 0.01){ //q0和p1在同一边
          setprimvertex(0, main_prim, flag, ptnum1);//移动面顶点的位置，但是顶点号的号码是不会变的
          setprimvertex(0, main_prim, flag + 1, ptnum2);
          new_prim = addprim(0, "poly", pts[flag], pts[flag + 1], ptnum2, ptnum1);
          tri_prim1 = addprim(0, "poly", pts[flag - 1], pts[flag], ptnum1);//侧边的面
          tri_prim2 = addprim(0, "poly", pts[flag + 1], pts[flag + 2], ptnum2);
          }else{ //q0和p2在同一边
          setprimvertex(0, main_prim, flag + 0, ptnum2);
          setprimvertex(0, main_prim, flag + 1, ptnum1);
          new_prim = addprim(0, "poly", pts[flag], pts[flag + 1], ptnum1, ptnum2);
          tri_prim1 = addprim(0, "poly", pts[flag-1], pts[flag], ptnum2);
          tri_prim2 = addprim(0, "poly", pts[flag + 1], pts[flag + 2], ptnum1);
        }
          //tri_prim1 attributes
          setprimgroup(0, "triangle", tri_prim1, 1, "set");
          setprimattrib(0, "join_head", tri_prim1, -1, "set"); //initialvalue need to be set as "-1"
          setprimattrib(0, "join_tail", tri_prim1, -1, "set");
          setprimattrib(0, "trunk", tri_prim1, primnum, "set");
          setprimattrib(0, "heading", tri_prim1, dir, "set");
          setprimattrib(0, "twin", tri_prim1, -1, "set");
         
          //tri_prim2 attributes
          setprimgroup(0, "triangle", tri_prim2, 1, "set");
          setprimattrib(0, "join_head", tri_prim2, -1, "set");
          setprimattrib(0, "join_tail", tri_prim2, -1, "set");
          setprimattrib(0, "trunk", tri_prim2, primnum, "set");
          setprimattrib(0, "heading", tri_prim2, dir, "set");
          setprimattrib(0, "twin", tri_prim2, -1, "set");
          
          //set join_head and join_tail value
          join_head = dir.x + dir.z > 0.01 ? ptnum2 : ptnum1;
          join_tail = dir.x + dir.z > 0.01 ? ptnum1 : ptnum2;
          tan = point(0, "P", pts[flag - 1]) - point(0, "P", pts[flag]);
          width = length(tan)/2;
          
          //new_prim attributes
          setprimattrib(0, "N", new_prim, {0,1,0}, "set"); //normal
          setprimgroup(0, "roof", new_prim, 1, "set");
          setprimattrib(0, "twin", new_prim, main_prim, "set");
          setprimattrib(0, "trunk", new_prim, primnum, "set");
          setprimattrib(0, "dir", new_prim, dir, "set");
          setprimattrib(0, "join_head", new_prim, join_head, "set");
          setprimattrib(0, "join_tail", new_prim, -1, "set");
          setprimattrib(0, "width", new_prim, width, "set");
          
          //old prim main_prim attributes
          setprimgroup(0, "ceiling", main_prim, 0, "set"); //remove from group"ceiling"
          setprimgroup(0, "roof", main_prim, 1, "set"); // add to the newgroup "roof"
          setprimattrib(0, "twin", main_prim, new_prim, "set");
          setprimattrib(0, "trunk", main_prim, primnum, "set");
          setprimattrib(0, "dir", main_prim, dir, "set");
          setprimattrib(0, "join_tail", main_prim, join_tail, "set");
          setprimattrib(0, "width", main_prim, width, "set");
    
          setprimattrib(0, "branch", primnum, main_prim, "append");
          setprimattrib(0, "branch", primnum, new_prim, "append");
          break;
        }
      }

#### 3 \[Attribute Wrangle节点\]划分trunk面 ####

完整代码，跟之前branch的方法差不多，这里就不过多解释了。

int pts[], ptnum1, ptnum2, new_prim, tri_prim1, tri_prim2, join_head, join_tail;
    vector dir, q0, q1, p1, p2, src_minpos, src_maxpos, tmp_dir, tan;
    int prims[] = expandprimgroup(0, "ceiling"); //get trunk prims
    float width;
    foreach(int trunk_prim; prims){
            pts = primpoints(0, trunk_prim);
            getbbox(0, itoa(trunk_prim), src_minpos, src_maxpos);
            int branch_prims[] = prim(0, "branch", trunk_prim);
            dir = 0;
            q0 = point(0, "P", pts[0]);
            q1 = point(0, "P", pts[1]);
            foreach(int branch_prim; branch_prims){
                    dir += abs(prim(0, "dir", branch_prim));
            }
            if(dir.x > dir.z || abs(dir.z-dir.x) < 0.01 && src_maxpos.x-src_minpos.x < src_maxpos.z-src_maxpos.z+0.01){
                    p1 = set((src_minpos.x+src_maxpos.x)/2, src_minpos.y, src_minpos.z);
                    p2 = set((src_minpos.x+src_maxpos.x)/2, src_maxpos.y, src_maxpos.z);
                    ptnum1 = addpoint(0, p1);
                    ptnum2 = addpoint(0, p2);
                    tmp_dir = {0,0,1}; //p1p2's direction.
                    p1 = p1.zyx;
                    p2 = p2.zyx;
                    q0 = q0.zyx;
                    q1 = q1.zyx;
    
            }else{
                    p1 = set(src_minpos.x, src_minpos.y, (src_minpos.z+src_maxpos.z)/2);
                    p2 = set(src_maxpos.x, src_maxpos.y, (src_minpos.z+src_maxpos.z)/2);
                    ptnum1 = addpoint(0, p1);
                    ptnum2 = addpoint(0, p2);
                    tmp_dir = {1,0,0};
    
            }
            int flag = abs(q0.x - q1.x) <0.01;
            if(q0.x-p1.x <0.01){
                    setprimvertex(0, trunk_prim, flag, ptnum1);
                    setprimvertex(0, trunk_prim, flag+1, ptnum2);
                    new_prim = addprim(0, "poly", pts[flag], pts[flag+1], ptnum2, ptnum1);
                    tri_prim1 = addprim(0, "poly", pts[flag -1], pts[flag], ptnum1);
                    tri_prim2 = addprim(0, "poly", pts[flag+1], pts[flag+2], ptnum2);
            }else{
                    setprimvertex(0, trunk_prim, flag, ptnum2);
                    setprimvertex(0, trunk_prim, flag+1, ptnum1);
                    new_prim = addprim(0, "poly", pts[flag], pts[flag+1], ptnum1, ptnum2);
                    tri_prim1 = addprim(0, "poly", pts[flag-1], pts[flag], ptnum2);
                    tri_prim2 = addprim(0, "poly", pts[flag+1], pts[flag+2], ptnum1);
            }
            //tri_prim1 attributes
        setprimgroup(0, "triangle", tri_prim1, 1, "set");
        setprimattrib(0, "join_head", tri_prim1, -1, "set"); //initialvalue need to be set as "-1"
        setprimattrib(0, "join_tail", tri_prim1, -1, "set");
        setprimattrib(0, "trunk", tri_prim1, -1, "set");
        setprimattrib(0, "twin", tri_prim1, -1, "set");
          
        //tri_prim2 attributes
        setprimgroup(0, "triangle", tri_prim2, 1, "set");
        setprimattrib(0, "join_head", tri_prim2, -1, "set");
        setprimattrib(0, "join_tail", tri_prim2, -1, "set");
        setprimattrib(0, "trunk", tri_prim2, -1, "set");
        setprimattrib(0, "twin", tri_prim2, -1, "set");
    
        join_head = ptnum2;
        join_tail = ptnum1;
        tan = point(0, "P", pts[flag-1]) - point(0, "P", pts[flag]);
        width = length(tan)/2;
    
        //new_prim attributes
        setprimattrib(0, "N", new_prim, {0,1,0}, "set"); //normal 
          setprimgroup(0, "roof", new_prim, 1, "set");
          setprimattrib(0, "twin", new_prim, trunk_prim, "set");
          setprimattrib(0, "trunk", new_prim, -1, "set");
          setprimattrib(0, "branch", new_prim, branch_prims, "set");
          setprimattrib(0, "dir", new_prim, tmp_dir, "set");
          setprimattrib(0, "join_head", new_prim, join_head, "set");
          setprimattrib(0, "join_tail", new_prim, -1, "set");
          setprimattrib(0, "width", new_prim, width, "set");
          
          //old prim trunk_prim attributes
          setprimgroup(0, "ceiling", trunk_prim, 0, "set"); //remove from group"ceiling"
          setprimgroup(0, "roof", trunk_prim, 1, "set"); // add to the newgroup "roof"
          setprimattrib(0, "twin", trunk_prim, new_prim, "set");
          setprimattrib(0, "trunk", trunk_prim, -1, "set");
          setprimattrib(0, "dir", trunk_prim, tmp_dir, "set");
          setprimattrib(0, "join_tail", trunk_prim, join_tail, "set");
          setprimattrib(0, "width", trunk_prim, width, "set");
    }

#### 4 \[Attribute Wrangle节点\]调整branch的trunk面 ####

这一步骤主要是因为一个trunk面会被划分成两个面，也就是有个twin面，之后要让branch对应的是原来的turnk还是trunk的twin对应的更精确。

**Group** 是 roof 和 triangle

这里的 **Group Type** 和 **Run Over** 都是 Primitive，也就是对于每个面都走一遍这个代码

vector src_minpos, src_maxpos, dst_minpos, dst_maxpos;
    if(len(i[]@branch) == 0){ // this prim has no branch
            i[]@branch = prim(0, "branch", prim(0, "twin", @primnum)); //这个面的twin面的branch
    } 
    if(i@trunk >= 0){ //this prim has its trunk 
            getbbox(0, itoa(@primnum), src_minpos, src_maxpos);
            getbbox(0, itoa(i@trunk), dst_minpos, dst_maxpos);
            if(abs(dst_maxpos.z - src_minpos.z) < 0.01 || abs(src_maxpos.z - dst_minpos.z) <0.01){
                    if(src_maxpos.x <dst_maxpos.x + 0.01 && src_minpos.x + 0.01 >dst_minpos.x){
                            return;//
                    }
            }else if(abs(dst_maxpos.x - src_minpos.x) < 0.01 || abs(src_maxpos.x - dst_minpos.x) <0.01){
                    if(src_maxpos.z <dst_maxpos.z + 0.01 && src_minpos.z + 0.01 >dst_minpos.z){
                            return;
                    }
            }
            i@trunk = prim(0, "twin", i@trunk);//则trunk的twin成为当前branch面的真正的trunk
    }

#### 5 \[Group Delete节点\]删除不用的group ####

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_16_color_FFFFFF_t_70_g_se_x_16][]

#### 6 \[Attribute Wrangle节点\]划分每个roof面的level高度 ####

这一步很重要，关系到后期拉高每个面的高度的步骤，建议自己看教程的P4部分

int roofs[], levels[];
    int trunk, branch[], level, twin, init_level, cur;
    
    void cut_loops(int trunk; int twin){ //提前规定一个函数，用来
            setprimattrib(0, "trunk", trunk, -1, "set");
            setprimattrib(0, "trunk", twin, -1, "set");
            setprimattrib(0, "join_head", trunk, -1, "set");
            setprimattrib(0, "join_head", twin, -1, "set");
            setprimattrib(0, "join_tail", trunk, -1, "set");
            setprimattrib(0, "join_tail", twin, -1, "set");
    //^ 符号的作用：比较两个值如果相同则为0，如果不同则为1  
            int join_head, join_tail;
            join_head = -1 ^ prim(0, "join_head", trunk) ^ prim(0, "join_head", twin);
            join_tail = -1 ^ prim(0, "join_tail", trunk) ^ prim(0, "join_tail", twin);
            setpointattrib(0, "heading", join_head, {0,0,0}, "set");
            setpointattrib(0, "heading", join_tail, {0,0,0}, "set");
    
    //delete branch
        int ttrunk = prim(0, "trunk", trunk);
        int ttwin = prim(0, "twin", trunk);
        int trunk_branch[] = prim(0, "branch", ttrunk);
        removevalue(trunk_branch, trunk);
        removevalue(trunk_branch, twin);
        setprimattrib(0, "branch", ttrunk, trunk_branch, "set");
        setprimattrib(0, "branch", ttwin, trunk_branch, "set");
            }
    roofs = expandprimgroup(0, "roof");
    resize(levels, max(roofs)+1);//change the array:levels[]'s size 
    foreach(int pr; roofs){
        trunk = prim(0, "trunk", pr);//current_prim's trunk
            int count = 0;
            while(trunk != -1){ // if there is a loop include current_prim : 
                if(trunk == pr){ //find which prim's trunk is the first prim?
                    push(loops, pr);//add prim-pr to array loops[];
                            break;
                    }
                    trunk = prim(0, "trunk", trunk);
                    count ++;
                    if(count >= len(roofs)) break;  
            }
    } 
    //now we have loops[], roofs[], levels[]
    while(len(roofs)){
            trunk = pop(roofs, 0);//remove the prim at 0 and returns it
            push(roofs, trunk);//add trunk to the end of roofs[]
            branch = prim(0, "branch", trunk);
            if(len(branch) && len(roofs) > len(loops)) continue;
    //we want to get a prim with no branch:
    level = 0;
    while(removevalue(roofs, trunk)){
            twin = prim(0, "twin", trunk);
            removevalue(roofs, twin);//do the same thing to the twin-prim
            if(removevalue(loops, trunk)){
                    removevalue(loops, twin);
            }else{// this trunk-prim can be the next one when do the levelup
                    level++;
                    levels[trunk] = levels[twin] = level;
            }
            trunk = prim(0, "trunk", trunk);
            }
    //get back to the first prim: 
    if(trunk >=0 && level++ > levels[trunk]){
            init_level = levels[trunk];
            level = level - init_level; 
            cur = trunk;
            while(prim(0, "trunk", cur) != trunk){
    //if init_level=0, levels[cur]=levels[cur]+level &&level++;
                    levels[cur] += init_level ? level : level++;
                    cur = prim(0, "trunk", cur);
            }
            levels[cur] += level;
            if(!init_level){
                    twin = prim(0, "twin", cur);
                    cut_loops(cur, twin);//cut the last prim in the loop
            }
    }
    }
    for(int i=0;i<len(levels);i++){
            if(levels[i]){
                    setprimattrib(0, "level", i, levels[i], "set");
            }
    }

### 用到的节点 ###

#### 1.facet节点 ####

[Facet (sidefx.com)][Facet _sidefx.com]

Facet节点的主要作用是处理点或面的法线（normal）的相关操作，当导入一些杂乱的平面时facet可以用来整理（**consolidate**）平面的点和翻转的法线。

其中**Unique Points**选项可用来给所有面的顶点**vertices**创建自己的**points**，让面不共享points。

### 用到的VEX function ###

#### 1.expandprimgroup ####

[expandprimgroup (sidefx.com)][expandprimgroup _sidefx.com]

expandprimgroup(geometry, "groupname"); //其中groupname是个string类型，返回这个group里primitive的number，返回的是一个数组。

#### 2.primpoints ####

[primpoints (sidefx.com)][primpoints _sidefx.com]

int \[\] primpoints(geometry, primnum);// 其中primnum是int类型的面号，返回面号为primnum的面里的所有点。

#### 3.getbbox ####

[getbbox (sidefx.com)][getbbox _sidefx.com]

getbbox(geometry,&min,&max); // 得到这个几何体bounding box的最小边界值和最大边界值，这个&min和&max的类型是vector，也就是向量类型，目标检测中bounding box的VOC边框表示法就是**(x\_min,y\_min,x\_max,y\_max)**,因此返回的值可以理解为点的坐标。

#### 2.itoa ####

[itoa (sidefx.com)][itoa _sidefx.com]

itoa(int类型的变量); //将整数转换成字符串string类型

#### 3.addpoint ####

[addpoint (sidefx.com)][addpoint _sidefx.com]

addpoint(geometry,point\_number); //创建一个跟点号为point\_number具有相同属性和组关系的新点

addpoint(geometry,position); //后面的position是个vector，在几何体添加一个位置是position的点

#### 4.set ####

[set (sidefx.com)][set _sidefx.com]

vector2- set(v1,v2)

vector- set(v1,v2,v3)

... 创建一个vector或matrix（向量或矩阵）

#### 5.setprimvertex ####

[setprimvertex (sidefx.com)][setprimvertex _sidefx.com]

把几何体的一个顶点vertex变成另一个不同的点

setprimvertex(geometry,prim,vertex\_of\_prim,point);// 把面prim上的顶点vertexofprim变成point，其中vertex\_of\_prim是面的顶点号

[Houdini_bilibili]: https://www.bilibili.com/video/BV1Ly4y1i7Vx?share_source=copy_web
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_13_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/a2e097c67c7b47fda8ea65d9b90b3887.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBAZmxhc2hpbmdnZw==,size_13,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_11_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/cf7a73406b46490e9d9708a2642e459a.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBAZmxhc2hpbmdnZw==,size_11,color_FFFFFF,t_70,g_se,x_16
[Houdini_-CSDN]: http://t.csdn.cn/RoN2v
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_15_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/410057a102074f0a92770134fdaf37da.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBAZmxhc2hpbmdnZw==,size_15,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBAZmxhc2hpbmdnZw_size_16_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/a40959f4fb7e4cfab3ab096713fa338f.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBAZmxhc2hpbmdnZw==,size_16,color_FFFFFF,t_70,g_se,x_16
[Facet _sidefx.com]: https://www.sidefx.com/docs/houdini/nodes/sop/facet.html
[expandprimgroup _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/expandprimgroup.html
[primpoints _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/primpoints.html
[getbbox _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/getbbox.html
[itoa _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/itoa.html
[addpoint _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/addpoint.html
[set _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/set.html
[setprimvertex _sidefx.com]: https://www.sidefx.com/docs/houdini/vex/functions/setprimvertex.html