Re: Allowing point to be outside the window?

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: dick.r.chiang@gmail.com,  emacs-devel@gnu.org
>> Date: Sun, 05 Dec 2021 17:15:25 +0800
>> 
>> >> I meant to ask whether or not I can forgo calculating whether point is
>> >> outside the window, and just test whether or not cursor.vpos is -1 to
>> >> determine if the cursor should be displayed, when point is allowed to be
>> >> outside the window.
>> >
>> > No.  I think it should be the other way around: first see if point is
>> > outside of the window, then force cursor.vpos to be negative.  That's
>> > because redisplay resets that value to -1 whenever it isn't sure the
>> > cursor will stay in its old position.
>> 
>> Thanks.  Another question or two: I can't use the value "-1" for
>> cursor.vpos to indicate that point is outside the window, as it's
>> already treated specially by redisplay, correct?
>
> No, you can't.  But the question is why do you need to?  -1 there
> means the cursor position is unknown.  Why do you need to know more
> than that, plus the fact that point is _allowed_ to be outside of the
> window?
>
>> Also, where should I put the code to test if cursor is invisible?  I
>> think it should be after the label force_start, as forcing the start
>> could potentially adjust point to be inside the window.
>
> It goes back to the same question I asked above: why do you need to
> know that point is outside of the window? for what purposes?
>
> IOW, why not just let redisplay do its thing, without bothering to
> bring point into the window, when that is allowed?

I need to erase the phys cursor and to tell display_and_set_cursor to
not draw it: otherwise, the ghost of the cursor remains on-screen even
after point is moved out.

Thanks.