Re: Allowing point to be outside the window?

[Po Lu <luangruo@yahoo.com>]

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 15:16:13 +0800
>> 
>> >> Can that value be relied on?
>> >
>> > Depends what for and how you want to rely on it.  It basically says
>> > that the cursor position inside the window is unknown.  The "normal"
>> > redisplay must always calculate some reasonable coordinates and put
>> > them there, otherwise the cursor will not be visible, which is a
>> > display bug.  If that is enough for you, then yes, you can rely on it.
>> 
>> 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?

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.