Cannot assign to gl_ClipDistance

[shamazmazum]

Minimal example:

(declaim (type varjo.internals:vertex-stage *vertex*))
(defparameter *vertex*
  (varjo:make-stage
   :vertex
   '((position :vec3))
   '()
   '(:430)
   `((setf (aref vari:gl-clip-distance 0) 0.0)
     (values (vari:vec4 position 1)))))

(declaim (type varjo.internals:fragment-stage *fragment*))
(defparameter *fragment*
  (varjo:make-stage
   :fragment
   '()
   '()
   '(:450)
   '((values))))

(defparameter *program*
  (varjo:rolling-translate
   (list *vertex* *fragment*)))

What I get:

Varjo: Assignment failed as GL-CLIP-DISTANCE is readonly