Jey Stone

//pick a polygon face/primitive
int index = chi("Primitive_Index");

//this array will hold newly created points
i[]@newpt_list;

//let's extrude the selected primitive (using Primitive
//Index we created above)
if(@primnum == index){
    
    //set selected prim color to white - just a visual aid
    @Cd = {1,1,1};
    
    //primpoints function gives us all the connected 
    //points, as index values
    i[]@conn_pts = primpoints(0,@primnum);
    
    //let's run through this points list, and then
    //create a new point above them
    foreach (int pt;@conn_pts) {
        
        //get the connected points position vector
        vector curr_pos = point(0,"P",pt);
        
        //create an offset vector, this will be our extrude amount
        //vector offset = set(0,chf("offset"),0);
        vector offset = @N;
        
        //calculate the new position, adding old pos with offset
        vector new_pos = curr_pos + offset;
        
        //create a new point at this new position vector
        int newpt = addpoint(geoself(),new_pos);
        
        //add the new point index to an array, will need these indexes
        //to create the top and side faces
        append(@newpt_list,newpt);
        
    }
    
    int len_conn = len(@conn_pts);
    int len_newpt = len(@newpt_list);
    
    for (int i=0;i<len_newpt;i++)
    {
        addprim(0,"poly",@conn_pts[len_newpt-(i+1)],@newpt_list[len_newpt-(i+1)],@newpt_list[len_newpt-(i+2)],@conn_pts[len_newpt-(i+2)]); 
    }    
    
    //create the 'side' poly faces - this bit needs more 'elegance'
    //addprim(0,"poly",@conn_pts[3],@newpt_list[3],@newpt_list[2],@conn_pts[2]); 
    //addprim(0,"poly",@conn_pts[2],@newpt_list[2],@newpt_list[1],@conn_pts[1]); 
    //addprim(0,"poly",@conn_pts[1],@newpt_list[1],@newpt_list[0],@conn_pts[0]); 
    //addprim(0,"poly",@newpt_list[0],@newpt_list[3],@conn_pts[3],@conn_pts[0]); 
    
    //remove the original prim face
    removeprim(geoself(),@primnum,0);
    
    //create the new 'top' poly face
    addprim(0,"poly",@newpt_list);   

}
//color non-selected prims blue, visual aid
else{
    @Cd = {0,0.5,1};
}