;;; Hüllpolygon
;;; Grobentwurf 7.11.2015
;;; Autor jupa
;;; Starten mit "hp"

(defun c:hp (/ Punkte P-Start P-lfd P-last W-Liste Erg-Liste W-last)

;;; Punktliste erzeugen; an konkrete Aufgabe anpassen

  (defun P_Liste (/ p_in Punktliste)
    (while (setq p_in (getpoint "\nPunkt eingeben: "))
      (setq Punktliste (cons p_in Punktliste))
    )
  )

  
;;; Startpunkt (kleinster y-Wert) ermitteln

  (defun Startpunkt (P-Liste /)
    (car (vl-sort P-Liste
		  (function (lambda (x1 x2)
			      (< (cadr x1) (cadr x2))
			    )
		  )
	 )
    )
  )

  
;;; erzeuge Winkelliste

  (defun W_Liste (P1 PL W-temp / temp1 temp2)	; P1 = aktueller Punkt, PL = Punktliste, W-temp = W_last
    (setq temp1
	   (mapcar '(Lambda (x / w1)
		      (if (and (/= P1 x) (/= P-last x))
			(progn
			  (setq w1 (- (angle P1 x) W-temp))
			  (if (< w1 0)(setq w1 (+ w1 pi pi)))
			  (cons x w1)
			)
		     )
		    )
		   PL
	   )
    )
    (setq temp2
	   (vl-sort temp1
		    (function (lambda (x1 x2)
				(< (cdr x1) (cdr x2))
			      )
		    )
	   )
    )
    (while (= (car temp2) nil) (setq temp2 (cdr temp2)))
    temp2
  )


;;; Hauptprogramm

  (setq Punkte (P_Liste))
  (setq P-Start (Startpunkt Punkte))
  (setq P-lfd P-Start)
  (setq P-last P-Start)
  (setq W-last 0.0)
  (setq W-Liste (W_Liste P-lfd Punkte W-last))
  (setq Erg-Liste (cons P-Start Erg-Liste))
  (setq P-lfd (caar W-Liste))
  (setq W-last (angle P-last P-lfd))

  (while (/= P-lfd P-Start)
    (setq Erg-Liste (cons P-lfd Erg-Liste))
    (setq W-Liste (W_Liste P-lfd Punkte W-last))
    (setq P-last P-lfd)
    (setq P-lfd (caar W-Liste))
    (setq W-last (angle P-last P-lfd))
  )
  Erg-Liste

;;;  (command "_line")
;;;  (mapcar 'command Erg-Liste)
;;;  (command "s")
)