bug#68050: 29.1; Pixel scroll doesn't work on platforms that do not expose device-class.

bug#68050: 29.1; Pixel scroll doesn't work on platforms that do not expose device-class.

[Jared Finder via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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Pixel scroll does not work on many platforms, such as Windows and Mac as
they only expose device classes core-keyboard and core-pointer.
Additionally, I have found that for Wayland under WSL on the emacs-29
branch, both the touchpad and the mouse are reported with device-class
'mouse on my Thinkpad laptop.

The attached patch enables a user to specify arbitrary device classes
that should cause interpolated scrolling so they can fix any issues.
This enables a user to customize this to the behavior of their local
machine.

I am undecided if this should involve renaming the existing
pixel-scroll-precision-interpolate-mice option or if it is important to
stay backward compatible with customizations that changed that option
from its default, t, to some other non-nil value.  Please give feedback
here.

Otherwise, this is a straightforward change that I think would be good
for the Emacs 29 branch so all platforms can get the smoothness of
interpolated pixel scrolling.

In GNU Emacs 29.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.37,
  cairo version 1.16.0) of 2023-09-11, modified by Debian built on melete
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
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  --sharedstatedir=/var/lib --libexecdir=/usr/libexec
  --localstatedir=/var/lib --infodir=/usr/share/info
  --mandir=/usr/share/man --with-libsystemd --with-pop=yes
  
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.1/site-lisp:/usr/share/emacs/site-lisp
  --with-sound=alsa --without-gconf --with-mailutils
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  --mandir=/usr/share/man --with-libsystemd --with-pop=yes
  
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.1/site-lisp:/usr/share/emacs/site-lisp
  --with-sound=alsa --without-gconf --with-mailutils
  --with-native-compilation --with-pgtk 'CFLAGS=-g -O2
  -ffile-prefix-map=/build/emacs-N816CI/emacs-29.1+1=. 
-fstack-protector-strong
  -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
  -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP
NOTIFY INOTIFY PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM GTK3 ZLIB

Important settings:
   value of $LANG: en_US.UTF-8
   locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
   global-window-tool-bar-mode: t
   pixel-scroll-precision-mode: t
   recentf-mode: t
   global-subword-mode: t
   global-form-feed-st-mode: t
   icomplete-mode: t
   fido-mode: t
   electric-pair-mode: t
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   cua-mode: t
   bar-cursor-mode: t
   url-handler-mode: t
   global-eldoc-mode: t
   show-paren-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   context-menu-mode: t
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   blink-cursor-mode: t
   window-divider-mode: t
   buffer-read-only: t
   column-number-mode: t
   line-number-mode: t
   transient-mark-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t

Load-path shadows:
None found.

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Memory information:
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From dfb4e33e9ed40c364a11f5faf23f3e7b87b88d54 Mon Sep 17 00:00:00 2001
From: Jared Finder <jared@finder.org>
Date: Tue, 26 Dec 2023 12:44:40 -0800
Subject: [PATCH] Allow interpolation with arbitrary device classes

* lisp/pixel-scroll.el (pixel-scroll-precision-interpolate-mice)
(pixel-scroll-precision-interpolate-devices): Change boolean option to
list so it can support mulitple device class symbols and rename it for
clarity.
* (pixel-scroll--interpolate-based-on-device-class-p): New function for
backward compatibile check against above option.
* (pixel-scroll-precision): Call it.
---
 lisp/pixel-scroll.el | 46 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/lisp/pixel-scroll.el b/lisp/pixel-scroll.el
index 5f412bf418a..f82f95153b5 100644
--- a/lisp/pixel-scroll.el
+++ b/lisp/pixel-scroll.el
@@ -212,13 +212,31 @@ pixel-scroll-precision-interpolate-page
   :type 'boolean
   :version "29.1")
 
-(defcustom pixel-scroll-precision-interpolate-mice t
-  "Whether or not to interpolate scrolling from a mouse.
-If non-nil, scrolling from the mouse wheel of an actual mouse (as
-opposed to a touchpad) will cause Emacs to interpolate the scroll."
+(define-obsolete-variable-alias
+  'pixel-scroll-precision-interpolate-mice
+  'pixel-scroll-precision-interpolate-devices
+  "29.2")
+
+(defcustom pixel-scroll-precision-interpolate-devices (list 'mouse)
+  "List of device classes that will cause interpolated scrolling.
+Interpolated scrolling looks good for devices that generate
+significant scroll distance per event, such as mice, and looks
+poor for devices that have ery small distance events, such as
+high precision touchpads.
+
+See `device-class' for possible device classes.
+
+For backward compatibility, this also can be set to t, which is
+equivalent to '(mouse)."
   :group 'scrolling
-  :type 'boolean
-  :version "29.1")
+  :type '(list
+          (checklist :inline t
+                     (const :tag "Mouse" mouse)
+                     (const :tag "Generic pointing device" core-pointer))
+          (repeat :inline t
+                  :tag "Other devices"
+                  symbol))
+  :version "29.2")
 
 (defun pixel-scroll-in-rush-p ()
   "Return non-nil if next scroll should be non-smooth.
@@ -700,10 +718,8 @@ pixel-scroll-precision
             (if (> (abs delta) (window-text-height window t))
                 (mwheel-scroll event nil)
               (with-selected-window window
-                (if (or (and pixel-scroll-precision-interpolate-mice
-                             (eq (device-class last-event-frame
-                                               last-event-device)
-                                 'mouse))
+                (if (or (pixel-scroll--interpolate-based-on-device-class-p
+                         (device-class last-event-frame last-event-device))
                         (and pixel-scroll-precision-large-scroll-height
                              (> (abs delta)
                                 pixel-scroll-precision-large-scroll-height)
@@ -732,6 +748,16 @@ pixel-scroll-precision
                      (message (error-message-string '(end-of-buffer))))))))))
       (mwheel-scroll event nil))))
 
+(defun pixel-scroll--interpolate-based-on-device-class-p (class)
+  "Return whether this device class should always interpolate scrolling.
+CLASS is a value returned from `device-class'."
+  (and pixel-scroll-precision-interpolate-devices
+       (memq class
+             (if (eq pixel-scroll-precision-interpolate-devices t)
+                 ;; Emacs 29.1 had this as a boolean, defaulting to t.
+                 '(mouse)
+               pixel-scroll-precision-interpolate-devices))))
+
 ;; isearch-scroll support
 (put 'pixel-scroll-precision 'scroll-command t)
 
-- 
2.39.2

bug#68050: 29.1; Pixel scroll doesn't work on platforms that do not expose device-class.

[Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Jared Finder <jared@finder.org> writes:

> Pixel scroll does not work on many platforms, such as Windows and Mac as
> they only expose device classes core-keyboard and core-pointer.
> Additionally, I have found that for Wayland under WSL on the emacs-29
> branch, both the touchpad and the mouse are reported with device-class
> 'mouse on my Thinkpad laptop.

Incidentally we don't support WSL, as circumventing their bugs for a
proprietary platform which Emacs already supports through the Cygwin and
native Windows builds is an unjustified burden.

> The attached patch enables a user to specify arbitrary device classes
> that should cause interpolated scrolling so they can fix any issues.
> This enables a user to customize this to the behavior of their local
> machine.
>
> I am undecided if this should involve renaming the existing
> pixel-scroll-precision-interpolate-mice option or if it is important to
> stay backward compatible with customizations that changed that option
> from its default, t, to some other non-nil value.  Please give feedback
> here.
>
> Otherwise, this is a straightforward change that I think would be good
> for the Emacs 29 branch so all platforms can get the smoothness of
> interpolated pixel scrolling.

pixel-scroll-precision-mode is first and foremost designed for devices
such as touchpads, for which interpolation is unnecessary as detailed
scrolling deltas are always reported within events they generate.

Interpolation for wheel mice is an afterthought, so to speak, and if the
code responsible for interfacing with the window system cannot detect
wheel mice by itself, then the option
pixel-scroll-precision-large-scroll-height might be set to a value
suitable for wheel mice to be distinguished from touchpads and for
interpolation to be applied to them.

When a predicated fallback mechanism is already in place, there's no
need for one that's far more coarse.  Furthermore, p-s-p-l-s-h can be
set to 0, which would be identical to setting this variable to t.

Thanks, but this isn't necessary.  Closing.

bug#68050: 29.1; Pixel scroll doesn't work on platforms that do not expose device-class.

[Jared Finder via Bug reports for GNU Emacs, the Swiss army knife of text editors]

On 2023-12-26 17:25, Po Lu wrote:
> Jared Finder <jared@finder.org> writes:
> 
>> Pixel scroll does not work on many platforms, such as Windows and Mac 
>> as
>> they only expose device classes core-keyboard and core-pointer.
>> Additionally, I have found that for Wayland under WSL on the emacs-29
>> branch, both the touchpad and the mouse are reported with device-class
>> 'mouse on my Thinkpad laptop.
> 
> Incidentally we don't support WSL, as circumventing their bugs for a
> proprietary platform which Emacs already supports through the Cygwin 
> and
> native Windows builds is an unjustified burden.

Understood.  However, I see the same issue on pure Windows and on Mac as 
well.

>> The attached patch enables a user to specify arbitrary device classes
>> that should cause interpolated scrolling so they can fix any issues.
>> This enables a user to customize this to the behavior of their local
>> machine.
>> 
>> I am undecided if this should involve renaming the existing
>> pixel-scroll-precision-interpolate-mice option or if it is important 
>> to
>> stay backward compatible with customizations that changed that option
>> from its default, t, to some other non-nil value.  Please give 
>> feedback
>> here.
>> 
>> Otherwise, this is a straightforward change that I think would be good
>> for the Emacs 29 branch so all platforms can get the smoothness of
>> interpolated pixel scrolling.
> 
> pixel-scroll-precision-mode is first and foremost designed for devices
> such as touchpads, for which interpolation is unnecessary as detailed
> scrolling deltas are always reported within events they generate.
> 
> Interpolation for wheel mice is an afterthought, so to speak, and if 
> the
> code responsible for interfacing with the window system cannot detect
> wheel mice by itself, then the option
> pixel-scroll-precision-large-scroll-height might be set to a value
> suitable for wheel mice to be distinguished from touchpads and for
> interpolation to be applied to them.
> 
> When a predicated fallback mechanism is already in place, there's no
> need for one that's far more coarse.  Furthermore, p-s-p-l-s-h can be
> set to 0, which would be identical to setting this variable to t.
> 
> Thanks, but this isn't necessary.  Closing.

I'm a bit confused by the "this isn't necessary" response.  What should 
I be doing on Mac or on Windows, where Emacs doesn't distinguish between 
touchpads and mice currently?  Is there a fix in the works for these 
OSes?

   -- MJF

bug#68050: 29.1; Pixel scroll doesn't work on platforms that do not expose device-class.

[Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Jared Finder <jared@finder.org> writes:

> I'm a bit confused by the "this isn't necessary" response.  What
> should I be doing on Mac or on Windows, where Emacs doesn't
> distinguish between touchpads and mice currently?  Is there a fix in
> the works for these OSes?

As I said, set pixel-scroll-precision-large-scroll-height to a value
such that events sent by mice are classified as such and interpolated,
or 0, which will direct Emacs to apply interpolation to all scroll
events.

bug#68050: 29.1; Pixel scroll doesn't work on platforms that do not expose device-class.

[Jared Finder via Bug reports for GNU Emacs, the Swiss army knife of text editors]

On 2023-12-26 18:03, Po Lu wrote:
> Jared Finder <jared@finder.org> writes:
> 
>> I'm a bit confused by the "this isn't necessary" response.  What
>> should I be doing on Mac or on Windows, where Emacs doesn't
>> distinguish between touchpads and mice currently?  Is there a fix in
>> the works for these OSes?
> 
> As I said, set pixel-scroll-precision-large-scroll-height to a value
> such that events sent by mice are classified as such and interpolated,
> or 0, which will direct Emacs to apply interpolation to all scroll
> events.

Thank you so much! This works as a replacement of my original patch.

   -- MJF