Re: pos-visible-in-window-p at ellipsis

[Richard Stallman]

    This happens because the pixel position reported by pos_visible_p can
    overshoot when there is invisible text (see the comment in
    xdisp.c:1321).  It would be rather complicated to compensate for this
    (and potentially buggy since pos_visible_p is used by many other
    functions).

Why is invisible text difficult?  Can't it just skip to the
next visible character?  (The comment doesn't say what is hard.)

      I think we should simply change the documentation of
    pos-visible-in-window-p to say that the pixel positions may not be
    accurate when there is invisible text at the specified position.

That is ok if this really is hard.  I just wonder why it is hard,
since it seems like it ought to be easy.