;;; ---------------------------------------------------------------------
;;;  FACE2PLN-bgol.lsp
;;;  Command:  F2PL
;;;
;;;  PURPOSE
;;;  Converts selected 3DFACE entities into equivalent closed 3D
;;;  polylines tracing the same vertices/outline. Unlocks area
;;;  calculation and other polyline-based tools on triangulated
;;;  surface data (a TIN of 3D faces), which the native AREA command
;;;  cannot operate on directly.
;;;
;;;  USAGE
;;;    1. Load this file (APPLOAD or drag-drop onto the drawing window).
;;;    2. Type   F2PL   at the command line and press Enter.
;;;    3. Select one or more 3DFACE entities.
;;;    4. Each 3DFACE is converted into an equivalent closed 3D
;;;       polyline on layer "BGOL-F2PL". The original 3DFACE entities
;;;       are left untouched.
;;;
;;;  NOTES
;;;    - This is an original, independently written implementation.
;;;      It is INSPIRED by the general idea of 3DFACE-to-polyline
;;;      conversion utilities common in CAD/survey drafting
;;;      workflows, but the code, command name and file name here are
;;;      new and are NOT copied from, nor identical to, any specific
;;;      third-party product.
;;;
;;;  ---------------------------------------------------------------------
;;;  Developed and shared for the CAD community by:  BGol Community
;;;  Community website:                              https://bgol.in/
;;;  License:  Open-source & free to use, modify, and share for all.
;;;            Provided "as is", without warranty of any kind.
;;;  ---------------------------------------------------------------------

(vl-load-com)

(defun BGOL:F2PL-EnsureLayer (lname / )
  (if (not (tblsearch "LAYER" lname))
    (entmake (list '(0 . "LAYER")
                   '(100 . "AcDbSymbolTableRecord")
                   '(100 . "AcDbLayerTableRecord")
                   (cons 2 lname)
                   '(70 . 0)
                   '(62 . 6)          ; magenta
                   '(6 . "Continuous")))
  )
)

;; Build a closed heavy 3D polyline (POLYLINE + VERTEX + SEQEND) through
;; a list of 3D points, skipping consecutive duplicate points.
(defun BGOL:F2PL-Make3DPoly (pts lname / uniq p prev)
  (setq uniq '())
  (setq prev nil)
  (foreach p pts
    (if (or (not prev) (> (distance p prev) 1e-8))
      (setq uniq (append uniq (list p)))
    )
    (setq prev p)
  )
  (if (and (> (length uniq) 2)
           (< (distance (car uniq) (last uniq)) 1e-8))
    (setq uniq (reverse (cdr (reverse uniq)))) ; drop duplicate closing pt
  )
  (if (>= (length uniq) 3)
    (progn
      (entmake (list '(0 . "POLYLINE")
                      '(100 . "AcDbEntity")
                      (cons 8 lname)
                      '(100 . "AcDb3dPolyline")
                      '(66 . 1)
                      '(70 . 9)        ; 3D polyline + closed
                      '(10 (0.0 0.0 0.0))
                )
      )
      (foreach p uniq
        (entmake (list '(0 . "VERTEX")
                        '(100 . "AcDbEntity")
                        (cons 8 lname)
                        '(100 . "AcDbVertex")
                        '(100 . "AcDb3dPolylineVertex")
                        (cons 10 p)
                        '(70 . 32)
                  )
        )
      )
      (entmake (list '(0 . "SEQEND") '(100 . "AcDbEntity") (cons 8 lname)))
      T
    )
    nil
  )
)

(defun BGOL:F2PL-FaceVerts (edata / p1 p2 p3 p4)
  (setq p1 (cdr (assoc 10 edata)))
  (setq p2 (cdr (assoc 11 edata)))
  (setq p3 (cdr (assoc 12 edata)))
  (setq p4 (cdr (assoc 13 edata)))
  (list p1 p2 p3 p4)
)

(defun C:F2PL ( / ss n i ename edata pts converted)
  (BGOL:F2PL-EnsureLayer "BGOL-F2PL")
  (princ "\nSelect 3DFACE entities to convert: ")
  (setq ss (ssget '((0 . "3DFACE"))))
  (if ss
    (progn
      (setq n (sslength ss))
      (setq converted 0)
      (setq i 0)
      (while (< i n)
        (setq ename (ssname ss i))
        (setq edata (entget ename))
        (setq pts (BGOL:F2PL-FaceVerts edata))
        (if (BGOL:F2PL-Make3DPoly pts "BGOL-F2PL")
          (setq converted (1+ converted))
        )
        (setq i (1+ i))
      )
      (princ (strcat "\nF2PL: " (itoa converted) " of " (itoa n)
                      " 3DFACE(s) converted to 3D polyline (layer BGOL-F2PL)."))
    )
    (princ "\nNo 3DFACE entities selected.")
  )
  (princ)
)

(princ "\nFACE2PLN-bgol.lsp loaded. Type F2PL to convert 3DFACE entities to 3D polylines.")
(princ "\n  -- Free & open-source, courtesy of BGol Community (https://bgol.in/) --")
(princ)