anchor.diff:  ;(in-package #:cl-foo)
   
   (require :sdl2)
  -(require :cl-opengl)
  -(require :cl-glu)
   
   (defparameter *width* 1280)
   (defparameter *height* 720)
  
positive.code:     (gl:enable :cull-face :lighting :light0 :depth-test)
      (gl:matrix-mode :projection)
      (gl:load-identity)
  ;    (gl:frustum -2 2 -2 2 1 10)
      (gl:ortho 0 2 0 2 -2 10)
  ;    (glu:perspective 45.0 *ratio* 0.1 10)
      (gl:matrix-mode :modelview)
  
negative.code:         (sdl2:gl-make-current win gl-context)
          (sdl2:hide-cursor)
          (init)
          (gl:clear :color-buffer :depth-buffer)
          ;; todo: polygon instead?
          (gl:begin :quad-strip)
          (gl:material :front :ambient-and-diffuse #(1.0 0.0 0.0 1.0))
          (gl:vertex 0.0 1.0 2.0)
          (gl:vertex 1.0 1.0 2.0)
          (gl:vertex 1.0 0.0 2.0)
          (gl:vertex 0.0 0.0 2.0)
          (gl:end)
          (gl:flush)
          (sdl2:gl-swap-window win)
  
          (sdl2:with-event-loop (:method :poll)
            (:keydown
  