float mindist = 999999.9;
int index = -1;
for(int i = 0; i< npoints(1); i++)
{
    vector pos = point(1, 'P', i);
    
    //float distance = sqrt(pow(pos.x - @P.x, 2)+pow(pos.z - @P.z,2));
    float distance = abs(pos.x - @P.x)+abs( pos.z - @P.z);
    
    if(mindist > distance)
    {
        mindist = distance;
        index = i;
    }
}

i@val = index;
f@dist = mindist;

dint vals[] = array();

int offset = -1;
int vts[] = primvertices(0, @primnum);
//i[]@vts = vts;
int vt0 = vts[0];
int pt0 = vertexpoint(0, vt0);
int val0 = point(0, 'val', pt0);

for(int i = 0; i<len(vts); i++)
{
    int vt = vts[i];
    int pt = vertexpoint(0, vt);
    int val = point(0, 'val', pt);
    
    int vt1 = vts[(i+1) % len(vts)];
    int pt1 = vertexpoint(0, vt1);
    int val1 = point(0, 'val', pt1);
    
    if(offset == -1 && val != val1)
    {
        offset = i; // get times when suffer different area value.
    }
    
    append(vals, val);
}



vals = sort(vals);  
int nvals[] = array(vals[0]);  // fill first element value.
for(int i = 0; i<len(vals)-1; i++)
{
    int val1 = vals[i];
    int val2 = vals[i+1];
    if(val1 != val2)
    {
        append(nvals, val2);
    }
}
i[]@nvals = nvals;

int poly = -1; // this condition defines the sequance of connecting line.
int count;  // polygon count
if(len(nvals) == 1)
{
    setprimattrib(0, 'val', @primnum, nvals[0]);
}
else
{
   removeprim(0, @primnum, 1);
   
   for(int i = offset; i<=len(vts) + offset; i++) 
   {
       int vt1 = vts[i % len(vts)];
       int vt2 = vts[(i+1) % len(vts)];
       
       int pt1 = vertexpoint(0, vt1);
       int pt2 = vertexpoint(0, vt2);
       
       vector pos1 = point(0, 'P', pt1);
       vector pos2 = point(0, 'P', pt2);
       
       int val1 = point(0, 'val', pt1);
       int val2 = point(0, 'val', pt2);
       
       if(val1 != val2)
       {
           int m_pt = addpoint(0, (pos1 + pos2)/2);
           
           if(poly < 0)
           {
               poly = addprim(0, 'poly');
               addvertex(0, poly, m_pt);
               setprimattrib(0, 'val', poly, val2);
               count = 1;
           }
           else
           {
               addvertex(0, poly, m_pt);
               count++;
               if(len(nvals) >= 3 && count == 3)
               {
                   setprimgroup(0, 'triangle', poly, 1);
               }
               poly = addprim(0, 'poly');
               setprimattrib(0, 'val', poly, val2);
               addvertex(0, poly, m_pt);
               count = 1;
           }
           
       }
       if(poly >= 0)
       {
           count++;
           addvertex(0, poly, pt2);
       }
       
   }
   
}

接下来，需要单独处理破洞的地方。先拾取生成好的模型面，翻转180度，用于填充 holes。

vector cen_pos = getbbox_center(0, itoa(@primnum));
int pts[] = primpoints(0, @primnum);

for(int i = 0; i<len(pts); i++)
{    
    vector pos = point(0, 'P', pts[i]);
    matrix mat = ident();
    rotate(mat, $PI, {0,1,0});
    
    pos -= cen_pos;
    pos *= mat;
    pos += cen_pos;
    
    setpointattrib(0, 'P', pts[i], pos ); 
}
setprimattrib(0, 'val', @primnum, i@val);