anchor.diff:                   (gl:enable-client-state :color-array)
                    (incf offset (* (vertex-buffer-nb-vertices vb) 4)))
                  (when (vertex-has-tex-coords (vertex-buffer-format vb))
  -                 (gl:active-texture 0)
  +                 (gl:active-texture :texture0)
                    (%gl:tex-coord-pointer 2 :float 0 (cffi:make-pointer (* offset elem-size)))
                    (gl:enable-client-state :texture-coord-array)
                    (incf offset (* (vertex-buffer-nb-vertices vb) 2)))
  
positive.code: (defun select-framebuffer (fb)
    (gl:bind-framebuffer-ext :framebuffer-ext (if fb (framebuffer-index fb) 0)))
  
  ;;; Primitive rendering
  (defstruct buffer
    index)
  
  
negative.code:              (gl:enable-client-state :index-array))
        (gl:disable-client-state :index-array)))
  
  (defun create-empty-index-buffer (nb-indices &key (usage :static-draw))
    (let ((buff (car (gl:gen-buffers 1))))
      (dformat "Creating index buffer: ~S~%" nb-indices)
      (dformat "Recommended # of indices: ~S~%" (gl:get-integer :max-elements-indices))
      (gl:bind-buffer :element-array-buffer buff)
      (%gl:buffer-data :element-array-buffer
                       (* nb-indices 2) ;; unsigned short
                       (cffi:null-pointer) ;; just allocating space
                       usage)
      (assert (= (gl::get-buffer-parameter :element-array-buffer :buffer-size :int)
                 (* nb-indices 2)))
      (let ((ib (make-index-buffer :index buff
                                   :nb-indices nb-indices)))
        ib)))
  
  (defun create-index-buffer (indices &key (usage :static-draw))
    (let ((ib (create-empty-index-buffer (length indices) :usage usage)))
      (index-buffer-update ib indices 0)
      ib))
  
  (defun index-buffer-update (ib array &optional (offset 0))
    (assert (< (+ offset (length array)) (index-buffer-nb-indices ib)))
    (gl:bind-buffer :element-array-buffer (index-buffer-index ib))
    (gl:with-mapped-buffer (p :element-array-buffer :write-only)
      (loop for i below (length array)
  