anchor.diff:    (ft :int))
   
   (defstruct image
  - data
  - width
  - height
  - maps
  - ft)
  + data width height maps ft)
   
   (defmethod translate-into-foreign-memory (object (type image-type) pointer)
     (with-foreign-slots ((data width height maps ft) pointer (:struct %image))
  
positive.code:  (depth-texture :boolean))
  
  (defstruct render-texture
   id
   texture
   depth
   depth-texture)
  
  (defmethod translate-into-foreign-memory (object (type render-texture-type) pointer)
    (with-foreign-slots ((id  depth-texture) pointer (:struct %render-texture))
  
negative.code:   (height :float))
  
  (defstruct rectangle
   x y width height)
  
  (defmethod translate-into-foreign-memory (object (type rectangle-type) pointer)
    (with-foreign-slots ((x y width height) pointer (:struct %rectangle))
  