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))))))))
              (lambda (x1 x2 y alpha)
                (declare (type fixnum x1 x2 y)
  
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)))))))))))
  
  ;;;
  
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))))))))))
  
  (defmacro def-fast-aa-render-xor-draw-span-fn (image-class)
  