anchor.diff:      
   (let ((coords (make-array 6 :element-type
   			  '(signed-byte 32))))
  -  (defun draw-triangle (tri &optional (renderer *renderer*))
  +  (defun draw-triangle (tri renderer)
       (loop for i below 3 do
   	 (let* ((tmat (sb-cga:matrix* *pmat* *vmat* *rotmat*))
   		(tv (sb-cga:transform-point 
  
positive.code: 	   ;;    (aref tri i) tv x y)
  	   (setf (aref coords (* 2 i))       (round x)
  		 (aref coords (1+ (* 2 i)))  (round y))))
      (let ((ptr (autowrap:ptr (sdl2-ffi.functions:sdl-get-window-surface *win*))))
        (loop for x below 8000 do
  	   (setf (cffi:mem-ref ptr :unsigned-char 
  			       (random 160000))
  			     (random 255))))
      (sdl2:render-draw-line 
       renderer
       (aref coords 0) (aref coords 1)
  
negative.code:       (sdl2:with-init (:everything)
  	(sdl2:with-window (win :title "Learn3D" :flags '(:shown)
  			       :w *x-res* :h *y-res*)
  			       
  	  (sdl2:with-renderer (renderer win :flags '(:accelerated :presentvsync))
  	    (sdl2:with-event-loop (:method :poll)
  	      (:idle
  	       ()
  