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From: Po Lu <luangruo@yahoo.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: rpluim@gmail.com,  emacs-devel@gnu.org
Subject: Re: master e37eb7f: Add support for pixel wheel deltas on NS
Date: Fri, 26 Nov 2021 19:44:59 +0800	[thread overview]
Message-ID: <877dcvf8ec.fsf@yahoo.com> (raw)
In-Reply-To: <83r1b32lvr.fsf@gnu.org> (Eli Zaretskii's message of "Fri, 26 Nov 2021 13:32:08 +0200")

Eli Zaretskii <eliz@gnu.org> writes:

> Thanks.  But if this conversion is arbitrary (see below), I think I
> know how to implement the MS-Windows version of "arbitrary".

Thanks!  I really appreciate it.

>> On X, the states of the mouse wheels in each axis are stored as absolute
>> values inside "valuators" attached to each mouse device.  To obtain the
>> delta of the scroll wheel from a motion event (which is used to report
>> that some valuator has changed), it is necessary to iterate over every
>> valuator that changed, and compare its previous value to the current
>> value of the valuator.
>> 
>> Each individual valuator also has an "interval", which is the amount you
>> must divide that delta by in order to obtain a delta in the terms of
>> scroll units.
>> 
>> This delta however is still intermediate, to make driver implementations
>> easier.  The XInput developers recommend the following algorithm to
>> convert from scroll unit deltas to pixel deltas:
>> 
>>   pixels_scrolled = pow (window_height, 2.0 / 3.0) * delta;
>
> All of this should be in comments in xterm.c.
>
> Btw, the code calculates pixels_scrolled when it is not yet clear that
> the value will be used, which is a waste of cycles, AFAICT.  How about
> moving this closer to where the value is actually used?

I'll do that, thanks.

> In any case, are you saying that the conversion to pixels is somewhat
> arbitrary?  And that users of X based systems have no control on this
> conversion, i.e. users cannot determine the pixel equivalent of each
> "delta"?

Yes, I'm using the method recommended by the XInput 2 developers, and on
X-based systems there's no option to control that arbitrary behaviour
that I know of.

It seems to be that every X-Windows program I checked (which includes
non-GTK programs such as Mozilla Firefox and Qt) also computes the pixel
information the same way.

>> Yes.  The PGTK port can do something similar if it gains support for
>> this, as GTK also reports it in pixels directly.

> Same question here: do users have any system-wide control on the
> conversion to pixels under these environments?

I don't know about NS, but there's no such option in GTK based systems.



  reply	other threads:[~2021-11-26 11:44 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20211125030922.2353.1129@vcs0.savannah.gnu.org>
     [not found] ` <20211125030924.7258E2094B@vcs0.savannah.gnu.org>
2021-11-25 10:26   ` master e37eb7f: Add support for pixel wheel deltas on NS Robert Pluim
2021-11-25 10:34     ` Po Lu
2021-11-25 10:47       ` Robert Pluim
2021-11-25 11:02       ` Eli Zaretskii
2021-11-26  0:39         ` Po Lu
2021-11-26  6:35           ` Eli Zaretskii
2021-11-26  7:00             ` Po Lu
2021-11-26  8:17               ` Eli Zaretskii
2021-11-26  9:37                 ` Po Lu
2021-11-26 11:32                   ` Eli Zaretskii
2021-11-26 11:44                     ` Po Lu [this message]
2021-11-26 16:55                       ` Eli Zaretskii
2021-11-27  0:02                         ` Po Lu
2021-11-27  6:09                           ` Eli Zaretskii
2021-11-27  6:41                             ` Po Lu
2021-11-27  7:05                               ` Eli Zaretskii
2021-11-27  7:14                                 ` Po Lu
2021-11-27 10:47                                   ` Eli Zaretskii
2021-11-27 10:54                                     ` Po Lu
2021-11-27 11:03                                       ` Eli Zaretskii
2021-11-27 11:05                                         ` Po Lu
2021-11-27 11:13                                           ` Po Lu
2021-11-27 11:32                                             ` Eli Zaretskii
2021-11-27 11:34                                               ` Po Lu
2021-11-27 11:40                                                 ` Eli Zaretskii
2021-11-27 11:44                                                   ` Po Lu
2021-11-27 12:02                                                     ` Eli Zaretskii
2021-11-27 12:11                                                       ` Po Lu
2021-11-27 12:36                                                         ` Eli Zaretskii
2021-11-27 12:48                                                           ` Po Lu
2021-11-26 11:48                     ` Eli Zaretskii
2021-11-26 12:05                       ` Po Lu
2021-11-26 12:23                         ` Eli Zaretskii
2021-11-26 12:37                           ` Po Lu
2021-11-26 19:39                             ` Alan Third
2021-11-26 19:45                               ` Eli Zaretskii
2021-11-26 19:54                                 ` Alan Third
2021-11-28  2:54                             ` Po Lu
2021-11-28  7:53                               ` Eli Zaretskii
2021-11-28  7:58                                 ` Po Lu
2021-11-28  8:28                                   ` Eli Zaretskii
2021-11-29  7:39                                     ` Po Lu
2021-11-29 12:50                                       ` Eli Zaretskii
2021-11-29 13:19                                         ` Po Lu
2021-11-25 11:00     ` Eli Zaretskii
2021-11-25 18:46       ` Stefan Monnier
2021-11-25 18:58         ` Eli Zaretskii

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