anchor.diff:  
     (defun init ()
       (gl:enable :depth-test)
  -    (gl:viewport 0 0 +width+ +height+)
  +    (gl:viewport 0 0 *width* *height*)
       (gl:matrix-mode :projection)
  -    (gl:ortho -2 2 -2 2 -2 2)
  +    (gl:ortho (- *x*) *x* (- *y*) *y* (- *x*) *x*)
       (gl:matrix-mode :modelview)
       (gl:load-identity)
       (gl:clear-color 19/255 19/255 39/255 1.0) ; #131327 background color
       (gl:clear :color-buffer :depth-buffer))
   
     (sdl2:with-init (:everything)
  -    (sdl2:with-window (win :w +width+ :h +height+ :flags '(:shown :opengl))
  +    (sdl2:with-window (win :w *width* :h *height* :flags '(:shown :opengl))
         (sdl2:with-gl-context (gl-context win)
           (sdl2:gl-make-current win gl-context)
           (init)
  
positive.code: 
  (require :sdl2)
  
  (defconstant +width+ 1280)
  (defconstant +height+ 720)
  
  (defun main-loop ()
    (defun keydown-actions (scancode)
  
negative.code:            (:keysym keysym)
             (keyup-actions (sdl2:scancode-value keysym)))
  
            ;; Draws a square.
            (:idle
             ()
             (gl:clear :color-buffer :depth-buffer)
             (gl:begin :quads)
             (gl:color 1.0 0.0 0.0)
             (gl:vertex -1.0 1.0 0.0)
             (gl:vertex 1.0 1.0 0.0)
             (gl:vertex 1.0 -1.0 0.0)
             (gl:vertex -1.0 -1.0 0.0)
             (gl:end)
             (gl:flush)
             (sdl2:gl-swap-window win))
  