anchor.diff:      (gui-slider-incf it dx)))
   
   (defmethod gui-widget-mouse-leave ((it gui-slider))
  -  (setf (gui-slider-sliding it) nil))+  (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)))))
  
positive.code: 
  (defun shutdown-gui ()
    (remove-input-handler *gui*)
    (setf *gui* nil))
  
  (defun render-gui ()
  
negative.code:    (pressed-texture :accessor gui-button-pressed-texture :initform nil
                      :initarg :pressed-texture))
    (:default-initargs
      :color (create-color 1 1 1)))
  
  ;; (key-handler gui-button (#\Return :press)
  ;;     (when (action it)
  