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 (x y alpha)
                (declare (type fixnum x 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))))))))
             (lambda (x1 x2 y alpha)
               (declare (type fixnum x1 x2 y)
  