int in_rectangle( // return true id 2D point p is in rectangle centered at C
  point p, 
  point c, 
  float w, 
  float h,
  
  float a, 

  output float dist, 
  output point uv
){
  point pr = rotate(p, a, c, c+vector(0,0,1));
  
  float x1=c[0]-w/2;
  float y1=c[1]-h/2;
  uv[0]=(pr[0]-x1)/w;
  uv[1]=(pr[1]-y1)/h;

  if(uv[0]>=0 && uv[0]<=1 && uv[1]>=0 && uv[1]<=1){
    dist=min(min(uv[0],1-uv[0]),min(uv[1],1-uv[1]));
    return 1;
  }
  return 0;
}

// bubble sort. fast enough for small collections
void sort(int np, output float z[], output vector p[], output float f[], output float g[], float h[]){
    int n=np;
    for(int j=0; j<np; j++){
       for(int i=1; i < n; i++){
          if( z[i-1] > z[i] ){
             float tz=z[i-1]; z[i-1]=z[i]; z[i]=tz;
             float tf=f[i-1]; f[i-1]=f[i]; f[i]=tf;
             float tg=g[i-1]; g[i-1]=g[i]; g[i]=tg;
             float th=h[i-1]; h[i-1]=h[i]; h[i]=th;
             point tp=p[i-1]; p[i-1]=p[i]; p[i]=tp;
          }
       }
       n--;
    }
}

shader greebles(
  point Pos=P,
  float Scale=1,
  float PositionVariance=1,
  float Size=0.3,
  float WidthVariance=0.1,
  float HeightVariance=0.1,
  float AngleVariance=0,
  
  int Seed=0,

  output float Fac=0,
  output float Bump=0,
  output float Dist=0,
  output vector UV=0
){
  point p=Pos*Scale;
  point ip=point(floor(p[0]), floor(p[1]), floor(p[2]));
  float z=-1;
  float vz[27];
  vector vp[27];
  float vx[27];
  float vy[27];
  float va[27];
  
  int n=0;
  for(float ix=ip[0]-1;ix<=ip[0]+1;ix++){
    for(float iy=ip[1]-1;iy<=ip[1]+1;iy++){
      for(float iz=ip[2]-1; iz<=ip[2]+1; iz++){
        vp[n] = vector(ix,iy,iz);
        vp[n] += PositionVariance*(vector)noise("cell",vp[n],Seed);
        vz[n] = noise("cell",vp[n],Seed+1);
        vx[n] = Size+WidthVariance*noise("cell",vp[n],Seed+2);
        vy[n] = Size+HeightVariance*noise("cell",vp[n],Seed+3);
        va[n] = AngleVariance*(2*noise("cell",vp[n],Seed+4)-1);
        n++;
      }
    }
  }
  sort(27, vz, vp, vx, vy, va);
  for(int n=0; n<27 && Fac == 0; n++){
    if(in_rectangle(p, vp[n], vx[n], vy[n], va[n], Dist, UV)){
      Fac=1;
      Bump=(float)(n+1)/28; // maybe add bevel based on distance
    }
  }
}