anchor.diff:     (pressed-texture :accessor gui-button-pressed-texture :initform nil
                       :initarg :pressed-texture))
     (:default-initargs
  -    :color (create-color 1 1 1)
  -    :texture (create-texture-from-file "button.png"
  -                                       :env-mode :replace)))
  +    :color (create-color 1 1 1)))
   
   ;; (key-handler gui-button (#\Return :press)
   ;;     (when (action it)
  
positive.code: 
  (defun shutdown-gui ()
    (remove-input-handler *gui*)
    (setf *gui* nil))
  
  (defun render-gui ()
  
negative.code:     (gui-slider-incf it dx)))
  
  (defmethod gui-widget-mouse-leave ((it gui-slider))
    (setf (gui-slider-sliding it) nil))
  
  
  (defclass gui-gauge (gui-widget)
    ((value :accessor gui-gauge-value :initform 0.5 :initarg :value)
     (fill-color :accessor gui-gauge-fill-color
                 :initform (create-color 1.0 1.0 1.0 0.75) :initarg :fill-color)))
  
  (defmethod render-widget ((w gui-gauge))
    (call-next-method)
    (set-color (gui-gauge-fill-color w))
    (gl:with-primitive :quads
      (gl:vertex (gl-x w) (gl-y w))
      (gl:vertex (+ (* (gui-gauge-value w) (width w)) (gl-x w))
                 (gl-y w))
      (gl:vertex (+ (* (gui-gauge-value w) (width w)) (gl-x w))
                 (- (gl-y w) (height w)))
      (gl:vertex (gl-x w) (- (gl-y w) (height w)))))
  