Re: The unwarranted scrolling assumption

[Lennart Borgman <lennart.borgman@gmail.com>]

On Sun, Jun 20, 2010 at 6:54 PM, Stephen J. Turnbull <stephen@xemacs.org> wrote:
> Lennart Borgman writes:
>
>  > I have done the best I can. I do not know what to do.
>
> Why don't you simply do what Eli asked, and test his patch?

I am going to do that but as far as I understand Eli has not in his
patch addressed the logic problems behind the "jumping scrolling".
However I gave a clear recipe for another scrolling bug and that is
what I assume Eli fixed so I am going to test that carefully.

> You seem to be terrified that it might work,

No, but I am clearly a bit upset because no one seem to be interested
in the logic. Juanma asked me to explain again more clearly to Eli. I
did. Where is the answer to my more detailed explanation?

> If it doesn't, you have no
> guarantee that your patch will go in.

I do not care about if my patch goes in. I just care about if the
problem gets fixed. And from David's testing it seems like it is not
fixed. But I will test anyway since I do not want to be unfair to Eli.
I do care that he tried to fix the problem.

> I agree from what you say that redisplay seems to be broken by design
> here, and a more comprehensive patch should be considered.

In my opinion the patch I sent is very simple.

Why don't you take a look at it? I mean the logic. I think you should
have no difficulties to see how the patch will look. Otherwise I can
make a clean version of the patch. This is anyway what I will do since
I will put it in my patched version for those who care.

> But I also
> agree with Eli that your proposed changes are scary (he might phrase
> that differently) because redisplay is really complex, and any
> substantial changes are likely to break something that is important to
> somebody.

I can understand that. I did look into some part of redisplay before
(because I was annoyed bye some part of the overlay handling and
invisibility).

The logic of my patch does however not change the inner logic of
redisplay in any way. It does change the interaction between clipping
and redisplay. It moves the whole responsibility to redisplay. There
is a possibility for one glitch (i.e. if my logic is correct): That
clipping changes occur between the last check of redisplay and display
finish. I think that fixing this kind of problem will not be too hard.

> By Murphy's law, this will only manifest itself the day
> before release.  You wouldn't want that, would you?

That is ok. Just fix it then before release ;-)

Or, to be more serious. Now is the time to fix it. We are far form the
version 24 release. (Just do not include it in next 23 series bug
fixes if any doubt remains.)

> So "fixing the jumping scroll" and "fixing redisplay" are two
> different things.  It is possible that Eli's patch will fix the
> particular bug(s) that this thread treats, while leaving the
> underlying design problem for later.

Yes of course. I may be wrong however I believe rather strongly the
efforts Eli has made can not cure the problem. (I think what Eli has
done may still be very good. It may of course also break redisplay, we
all make mistakes since human beings are unfortunately not very good
at logic, but I am not very worried and no one else seems worried
about it either.)