Re: mouse-wheel-scroll

[Richard Copley <rcopley@gmail.com>]

On 1 April 2017 at 15:29, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Richard Copley <rcopley@gmail.com>
>> Date: Fri, 31 Mar 2017 20:02:25 +0100
>> Cc: Dani Moncayo <dmoncayo@gmail.com>, Emacs Development <emacs-devel@gnu.org>
>>
>> On MS Windows, one WM_MOUSEWHEEL event doesn't always mean the same
>> as another. Programs need to examine the wParam to find the scroll
>> distance. As far as I can tell Emacs doesn't do that.
>
> Not sure what you mean by "examine wParam".  We do use the recommended
> GET_WHEEL_DELTA_WPARAM macro.

So we do. Good. Sorry, I missed that.

I had thought we were treating each message as single-notch scroll.
It seemed like that could explain some of the strange scroll speeds
reported. My mistake.

Apologies for the delayed response too.

>> This might (possibly) explain Kunihiro's results
>
> Were they on MS-Windows?  I'm not sure.

We'd have had to ask, but it's a moot point now as far as this idea is
concerned.

>> if what Raymond Chen calls a
>> "sub-detent mouse" was involved. (See "Scrollbars bart [sic] 6 – The wheel",
>> "https://blogs.msdn.microsoft.com/oldnewthing/20030807-00/?p=42963".)
>
> What that blog suggests, AFAIU, means that the amount of scrolling
> could not be controlled via the system customization interfaces, only
> via Emacs's user options.

I'm confused. The blog says "the amount of scrolling is a user setting
which must be respected", and the sample code "requeries the user's
desired scroll delta at each mouse wheel message". But I don't see
anything there that applies to Emacs's user options. They are outside
its scope.

> Is that what we want?  It would mean that
> Emacs behaves differently from other applications on the same system.

Confused again. The blog is only about the interpretation of wheel messages.
How we respond to the messages is under our control. What they mean is not.

I posted the blog because it's a good explanation of the basics (remember
from earlier that I stupidly thought I'd found a big mistake?) and to say
what a sub "detent wheel" was.