;;; ---------------------------------------------------------------------
;;;  PLDIST-bgol.lsp
;;;  Command:  PDIST
;;;
;;;  PURPOSE
;;;  Measures the true distance ALONG a polyline between two picked
;;;  points that both lie on it (rather than a straight-line distance
;;;  between them), without trimming or duplicating the polyline. Also
;;;  reports each individual segment length between intermediate
;;;  vertices for cross-checking.
;;;
;;;  USAGE
;;;    1. Load this file (APPLOAD or drag-drop onto the drawing window).
;;;    2. Type   PDIST   at the command line and press Enter.
;;;    3. Select the polyline (or 2D/3D polyline / lwpolyline) to
;;;       measure along.
;;;    4. Pick (or snap near) a Start Point and an End Point on that
;;;       polyline.
;;;    5. The routine reports the total path distance between the two
;;;       points, labels each intermediate vertex-to-vertex segment
;;;       length along the span, and places a total-distance label at
;;;       the midpoint — all on layer "BGOL-PDIST".
;;;
;;;  NOTES
;;;    - Uses vlax-curve-getParamAtPoint / getDistAtParam, so it
;;;      correctly follows curved (arc) segments as well as straight
;;;      ones.
;;;    - This is an original, independently written implementation.
;;;      It is INSPIRED by the general idea of "distance along a path"
;;;      measuring utilities common in survey/alignment 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:PDIST-EnsureLayer (lname / )
  (if (not (tblsearch "LAYER" lname))
    (entmake (list '(0 . "LAYER")
                   '(100 . "AcDbSymbolTableRecord")
                   '(100 . "AcDbLayerTableRecord")
                   (cons 2 lname)
                   '(70 . 0)
                   '(62 . 2)          ; yellow
                   '(6 . "Continuous")))
  )
)

(defun BGOL:PDIST-Text (pt txt ht lname / )
  (entmake (list '(0 . "TEXT")
                 '(100 . "AcDbEntity")
                 (cons 8 lname)
                 '(100 . "AcDbText")
                 (cons 10 pt)
                 (cons 40 ht)
                 (cons 1 txt)))
)

(defun C:PDIST ( / ent obj p1 p2 par1 par2 parLo parHi d1 d2 total
                    i vparam vpt vdist prevDist prevPt segLen midp)
  (BGOL:PDIST-EnsureLayer "BGOL-PDIST")
  (setq ent (car (entsel "\nSelect polyline: ")))
  (if ent
    (progn
      (setq obj (vlax-ename->vla-object ent))
      (setq p1 (getpoint "\nStart point (on polyline): "))
      (setq p2 (if p1 (getpoint "\nEnd point (on polyline): ")))
      (if (and p1 p2)
        (progn
          (setq par1 (vlax-curve-getParamAtPoint obj (vlax-curve-getClosestPointTo obj p1)))
          (setq par2 (vlax-curve-getParamAtPoint obj (vlax-curve-getClosestPointTo obj p2)))
          (setq parLo (min par1 par2))
          (setq parHi (max par1 par2))
          (setq d1 (vlax-curve-getDistAtParam obj parLo))
          (setq d2 (vlax-curve-getDistAtParam obj parHi))
          (setq total (abs (- d2 d1)))
          (setq midp (vlax-curve-getPointAtDist obj (+ d1 (/ total 2.0))))
          (BGOL:PDIST-Text midp (strcat "Total: " (rtos total 2 3)) 2.5 "BGOL-PDIST")
          ;; per-segment breakdown across integer vertex params in range
          (setq prevDist d1)
          (setq prevPt (vlax-curve-getPointAtDist obj d1))
          (setq i (1+ (fix parLo)))
          (while (<= i (fix parHi))
            (setq vparam (float i))
            (setq vpt (vlax-curve-getPointAtParam obj vparam))
            (setq vdist (vlax-curve-getDistAtParam obj vparam))
            (setq segLen (abs (- vdist prevDist)))
            (BGOL:PDIST-Text (mapcar '(lambda (a b) (/ (+ a b) 2.0)) prevPt vpt)
                              (rtos segLen 2 3) 2.0 "BGOL-PDIST")
            (setq prevDist vdist)
            (setq prevPt vpt)
            (setq i (1+ i))
          )
          (princ (strcat "\nPDIST: total distance along polyline = " (rtos total 2 3)))
        )
        (princ "\nStart/end point not given.")
      )
    )
    (princ "\nNo polyline selected.")
  )
  (princ)
)

(princ "\nPLDIST-bgol.lsp loaded. Type PDIST to measure distance along a polyline between two points.")
(princ "\n  -- Free & open-source, courtesy of BGol Community (https://bgol.in/) --")
(princ)