anchor.diff:                              (octet-blend-function (color-octet-xor r.bg r.fg) (color-octet-xor g.bg g.fg)
                                                     (color-octet-xor b.bg b.fg) (octet-mult a.fg alpha)
                                                     r.bg g.bg b.bg a.bg)
  +                          (declare (ignorable alpha))
                             ,(image-rgba-set-code image-class 'pixels 'x 'y 'red 'green 'blue 'alpha)))))))))))
   
   ;;;
  
positive.code:                        (octet-blend-function (color-octet-xor r.bg r.fg) (color-octet-xor g.bg g.fg)
                                               (color-octet-xor b.bg b.fg) (octet-mult a.fg alpha)
                                               r.bg g.bg b.bg a.bg)
                       ,(image-rgba-set-code image-class 'pixels 'x 'y 'red 'green 'blue 'alpha))))))))))
  
  (defmacro def-fast-aa-render-xor-draw-span-fn (image-class)
  
negative.code:                          (octet-blend-function (color-octet-xor r.bg r.fg) (color-octet-xor g.bg g.fg)
                                                 (color-octet-xor b.bg b.fg) (octet-mult a.fg alpha)
                                                 r.bg g.bg b.bg a.bg)
                         (declare (ignorable alpha))
                         ,(image-rgba-set-code image-class 'pixels 'x 'y 'red 'green 'blue 'alpha)))))))
             (lambda (x y alpha)
               (declare (type fixnum x y)
  