;; this file:
;;   https://dataswamp.org/~incal/common-lisp/general-base/polygon.lisp

(defvar *poly*)
(setq *poly* nil)

(defun init-poly ()
  (setq *poly* (gl:gen-lists 1))
  (gl:new-list *poly* :compile)
  (gl:push-matrix)
  (draw-polygon-test)
  (gl:pop-matrix)
  (gl:end-list) )

(defun draw-poly ()
  (unless *poly*
    (init-poly) )
  (gl:call-list *poly*) )

(defun draw-polygon (ps &optional r g b)
  (gl:with-primitive :polygon
    (let ((rnd))
      (if (and r g b)
          (gl:color r g b)
        (when (eq r 'random)
          (setf rnd t) ))
      (loop for (x y z) in ps do
        (when rnd (random-color))
        (gl:vertex x y z) ))))

(defun draw-polygon-test (&optional (vert 4))
  (let ((poly))
    (dotimes (_ vert)
      (push (random-xyz) poly) )
    (draw-polygon poly 'random) ))