anchor.diff:  
   (declaim (special *supplementary-framebuffer*
                     *depth-stencil-renderbuffer*))
  -
   
   
   (defvar *default-clear-color* (vec4 1 1 1 1))
  
positive.code:                  :height height
                   :samples samples))
  
  ;;;
  ;;; FRAMEBUFFER
  ;;;
  (defclass framebuffer (disposable)
    ((id :initform (gl:gen-framebuffer))))
  
  
  (defun delete-framebuffer (id)
  
negative.code: 
  (define-system-function make-framebuffer graphics-system ()
    (make-instance 'framebuffer :id (gl:gen-framebuffer)))
  
  
  (defun configure-framebuffer (framebuffer &rest attachments)
    (with-slots ((this-attachments attachments)) framebuffer
      (setf this-attachments attachments)))
  
  
  (defmethod %clear-rendering-output ((this framebuffer) color)
    (with-slots (bound-buffers) this
      (flet ((%clear ()
               (gl:clear-color (x color) (y color) (z color) (w color))
               (apply #'gl:clear bound-buffers)))
        (run-with-bound-output this #'%clear))))
  
  
  (defmethod run-with-bound-output ((output framebuffer) function)
  