anchor.diff:                                  (if (boundp '*light-decay-time*)
                                       *light-decay-time*
                                       0)))
  -  (when *current-framebuffer*
  +  (when (and *current-framebuffer*
  +             *light-position*)
       (let ((fb-addr (+ +physical-map-base+
                         (framebuffer-base-address *current-framebuffer*)
  +                      (if (eql *light-position* :bottom)
  +                          (* (1- (framebuffer-height *current-framebuffer*))
  +                             (framebuffer-pitch *current-framebuffer*))
  +                          0)
                         (* (light-index light) 32 4)))
             (colour (if (light-state light)
                         (light-colour light)
  
positive.code: 
  (defun clear-light (light)
    (setf (light-state light) nil)
    (when *current-framebuffer*
      (let ((fb-addr (+ +physical-map-base+
                        (framebuffer-base-address *current-framebuffer*)
                        (* (light-index light) 32 4))))
        (dotimes (i 32)
          (setf (sys.int::memref-unsigned-byte-32 fb-addr i) 0)))))
  
negative.code: (defvar *debug-video-col* 0)
  
  (defun initialize-early-video ()
    (when (not (boundp '*light-position*))
      (setf *light-position* :top))
    ;; Trash old framebuffer.
    (setf *current-framebuffer* nil)
    (setf *debug-video-x* 0
  