anchor.diff:  
   (require :sdl2)
   
  -(defconstant +width+ 1280)
  -(defconstant +height+ 720)
  +(defparameter *width* 1280)
  +(defparameter *height* 720)
  +(defparameter *zoom* 100)
  +(defparameter *x* (/ *width* *zoom*))
  +(defparameter *y* (/ *height* *zoom*))
   
   (defun main-loop ()
     (defun keydown-actions (scancode)
  
positive.code: 
    (defun init ()
      (gl:enable :depth-test)
      (gl:viewport 0 0 +width+ +height+)
      (gl:matrix-mode :projection)
      (gl:ortho -2 2 -2 2 -2 2)
      (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-gl-context (gl-context win)
          (sdl2:gl-make-current win gl-context)
          (init)
  
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))
  