anchor.diff:            (if colors     #x02 #x00)
             (if tex-coords #x04 #x00)
             (if normals    #x08 #x00)))
  +
  +(defun vertex-size (fmt)
  +  (+ (if (vertex-has-vertices fmt) 3 0)
  +     (if (vertex-has-colors fmt) 4 0)
  +     (if (vertex-has-tex-coords fmt) 2 0)
  +     (if (vertex-has-normals fmt) 3 0)))
   
   (defun vertex-has-vertices (fmt)
     (logbitp 0 fmt))
  
positive.code:                      (aref vertices (+ 2 (* i 3)))))))
  
  (defstruct display-list
    (index -1)
    primitive
    start end
    vb ib)
  
  (defun load-primitive (indices vertices &key (primitive :triangles)
                                               colors tex-coords normals
  
negative.code: (defun select-framebuffer (fb)
    (gl:bind-framebuffer-ext :framebuffer-ext (if fb (framebuffer-index fb) 0)))
  
  ;;; Vertex Buffer
  (defstruct buffer
    index)
  
  