anchor.diff:  		   :x1 x1
   		   :x2 x2
   		   :y1 y1
  -		   :y2 y2)))
  +		   :y2 y2
  +		   ;; default bounding volume is an AABB rectangle provide with
  +		   ;; the center-radius representation
  +		   :bounding-volume (make-instance 'collision-rectangle
  +						   :radius radius
  +						   :center-point center-point))))
   
   (defun make-rectangle (&optional
   			 (x 0.0)
  
positive.code: 
  ;; TODO: add texture coordinate to initilizations, providing a texture.png
  ;; and a fixed texture coordinate with texatl:with-sprite ?
  (defun make-rectangle-c (&optional
  			   (center-point (vec3 0.0 0.0 0.0))
  			   (radius (vec3 50.0 50.0 0.0)))
  
negative.code:    (tex-y1 :initarg :tex-y1 :type vec2 :initform (vec2 0.0 1.0))
     (tex-y2 :initarg :tex-y2 :type vec2 :initform (vec2 1.0 1.0))
  
     ;; Bounding Volume used for collision test - the proxy geometry
     ;; Now all transformation functions must also update this one
     (bounding-volume :initarg :bounding-volume :type collision-rectangle)
  
     ;; for now we directly couple animation with the rectangle
     (animation-state :type animation :initform (make-animation) :reader animation-state)))
  