bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Dear Emacs developers,

To reproduce starting from 'emacs -Q' visit an image file. Then
repeatedly use 'i +' till the image is taller than the window. The
image can be scrolled using mouse wheel. Now do

M-x pixel-scroll-precision-mode

After this attempting to scroll the image will set the vscroll to 0
and then image can't be scrolled at all.

From some investigation it seems like this behavior is not specific
to image-mode. Another way to reproduce the behavior is to evaluate
the following lisp code,

(let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
       (height (* (window-text-height win t) 2))
       (file "path/to/image"))
  (select-window win)
  (erase-buffer)
  (insert-image (create-image file nil nil))
  (goto-char 1)
  (pixel-scroll-precision-mode)
  nil)

This image thus displayed can not be scrolled. However if the code
above is slightly modified to insert a new line after the image,
scrolling can be done normally, i.e.

(let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
       (height (* (window-text-height win t) 2))
       (file "path/to/image"))
  (select-window win)
  (erase-buffer)
  (insert-image (create-image file nil nil))
  (insert "\n")
  (goto-char 1)
  (pixel-scroll-precision-mode)
  nil)

produces an image that can be scrolled. Inserting a newline after the
text covered by the text property holding the image also fixes the
problem in 'image-mode' but that doesn't seem like the right fix to me.

Rahguzar


In GNU Emacs 29.1 (build 1, x86_64-suse-linux-gnu, GTK+ Version 3.24.38,
 cairo version 1.17.8) of 2023-08-07 built on lamb11
System Description: openSUSE Tumbleweed

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bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Rahguzar <rahguzar@zohomail.eu> writes:

> Dear Emacs developers,
>
> To reproduce starting from 'emacs -Q' visit an image file. Then
> repeatedly use 'i +' till the image is taller than the window. The
> image can be scrolled using mouse wheel. Now do
>
> M-x pixel-scroll-precision-mode
>
> After this attempting to scroll the image will set the vscroll to 0
> and then image can't be scrolled at all.
>
>>From some investigation it seems like this behavior is not specific
> to image-mode. Another way to reproduce the behavior is to evaluate
> the following lisp code,
>
> (let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
>        (height (* (window-text-height win t) 2))
>        (file "path/to/image"))
>   (select-window win)
>   (erase-buffer)
>   (insert-image (create-image file nil nil))
>   (goto-char 1)
>   (pixel-scroll-precision-mode)
>   nil)
>
> This image thus displayed can not be scrolled. However if the code
> above is slightly modified to insert a new line after the image,
> scrolling can be done normally, i.e.
>
> (let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
>        (height (* (window-text-height win t) 2))
>        (file "path/to/image"))
>   (select-window win)
>   (erase-buffer)
>   (insert-image (create-image file nil nil))
>   (insert "\n")
>   (goto-char 1)
>   (pixel-scroll-precision-mode)
>   nil)
>
> produces an image that can be scrolled. Inserting a newline after the
> text covered by the text property holding the image also fixes the
> problem in 'image-mode' but that doesn't seem like the right fix to me.
>
> Rahguzar

This is a known limitation of pixel-scroll-precision-mode: redisplay's
automatic recentering impededs adjustment of the vscroll as the image
moves outside of the window's text area.  Unfortunately, it's not slated
to be fixed any time soon.

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Hi Po,
In this case it is not the recentering which is causing this problem,
it is rather the binding for next-pos in
pixel-scroll-precision-scroll-down-page which is the issue. The
binding signals an error when downward vertical motion is not
possible. However in this scenario scrolling can still be done.
Replacing that binding with desired-start allow me to scroll the
images.

This change for example allows for scrolling tall images,
@@ -524,10 +524,12 @@ pixel-scroll-precision-scroll-down-page
          (next-pos (save-excursion
                      (goto-char desired-start)
                      (when (zerop (vertical-motion (1+ scroll-margin)))
-                       (set-window-start nil desired-start)
-                       (signal 'end-of-buffer nil))
+                       (unless (let ((remaining-bottom (nth 3 (pos-visible-in-window-p desired-start nil t))))
+                                 (and remaining-bottom (not (zerop remaining-bottom))))
+                         (signal 'end-of-buffer nil)))
                      (while (when-let ((posn (posn-at-point)))
-                              (< (cdr (posn-x-y posn)) delta))
+                              (and (< (point) (point-min))
+                                   (< (cdr (posn-x-y posn)) delta)))
                        (when (zerop (vertical-motion 1))
                          (set-window-start nil desired-start)
                          (signal 'end-of-buffer nil)))

I am not sure it is the correct change since I don't understand the
while loop but comparing 'point' and 'point-min' doesn't seem the write
thing there. On the others hand if there is 'point-min' is 1 and
'point-max' 2, (cdr (posn-x-y posn))

Po Lu <luangruo@yahoo.com> writes:

> This is a known limitation of pixel-scroll-precision-mode: redisplay's
> automatic recentering impededs adjustment of the vscroll as the image
> moves outside of the window's text area.  Unfortunately, it's not slated
> to be fixed any time soon.

In this case it is not the recentering which is causing this problem,
it is rather the binding for next-pos in
pixel-scroll-precision-scroll-down-page which is the issue. The
binding signals an error when downward vertical motion is not
possible. However in this scenario scrolling can still be done.
Replacing that binding with desired-start allow me to scroll the
images.

This change for example allows for scrolling tall images,
@@ -524,10 +524,12 @@ pixel-scroll-precision-scroll-down-page
          (next-pos (save-excursion
                      (goto-char desired-start)
                      (when (zerop (vertical-motion (1+ scroll-margin)))
-                       (set-window-start nil desired-start)
-                       (signal 'end-of-buffer nil))
+                       (unless (let ((remaining-bottom (nth 3 (pos-visible-in-window-p desired-start nil t))))
+                                 (and remaining-bottom (not (zerop remaining-bottom))))
+                         (signal 'end-of-buffer nil)))
                      (while (when-let ((posn (posn-at-point)))
-                              (< (cdr (posn-x-y posn)) delta))
+                              (and (< (point) (point-min))
+                                   (< (cdr (posn-x-y posn)) delta)))
                        (when (zerop (vertical-motion 1))
                          (set-window-start nil desired-start)
                          (signal 'end-of-buffer nil)))

I am not sure it is the correct change since I don't understand the
while loop but comparing 'point' and 'point-min' doesn't seem the write
thing there. On the others hand if there is 'point-min' is 1 and
'point-max' 2, (cdr (posn-x-y posn)) is always zero, so that check makes
the loop terminate without signaling an error.

The behavior is also sub optimal in that it allows for scrolling past
the lower edge of the image but how much depends on the speed of the
scrolling, but that can be fixed easily.

Rahguzar

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

The diff in my last message was not correct, sorry about that. It should
be

@@ -524,12 +524,15 @@ pixel-scroll-precision-scroll-down-page
          (next-pos (save-excursion
                      (goto-char desired-start)
                      (when (zerop (vertical-motion (1+ scroll-margin)))
-                       (set-window-start nil desired-start)
-                       (signal 'end-of-buffer nil))
+                       (unless (let ((remaining-bottom (nth 3 (pos-visible-in-window-p desired-start nil t))))
+                                 (and remaining-bottom (not (zerop remaining-bottom))))
+                         (set-window-start nil desired-start t)
+                         (signal 'end-of-buffer nil)))
                      (while (when-let ((posn (posn-at-point)))
-                              (< (cdr (posn-x-y posn)) delta))
+                              (and (< (point) (point-min))
+                                   (< (cdr (posn-x-y posn)) delta)))
                        (when (zerop (vertical-motion 1))
-                         (set-window-start nil desired-start)
+                         (set-window-start nil desired-start t)
                          (signal 'end-of-buffer nil)))
                      (point)))
          (scroll-preserve-screen-position nil)

Rahguzar <rahguzar@zohomail.eu> writes:

> Hi Po,
> In this case it is not the recentering which is causing this problem,
> it is rather the binding for next-pos in
> pixel-scroll-precision-scroll-down-page which is the issue. The
> binding signals an error when downward vertical motion is not
> possible. However in this scenario scrolling can still be done.
> Replacing that binding with desired-start allow me to scroll the
> images.
>
> This change for example allows for scrolling tall images,
> @@ -524,10 +524,12 @@ pixel-scroll-precision-scroll-down-page
>           (next-pos (save-excursion
>                       (goto-char desired-start)
>                       (when (zerop (vertical-motion (1+ scroll-margin)))
> -                       (set-window-start nil desired-start)
> -                       (signal 'end-of-buffer nil))
> +                       (unless (let ((remaining-bottom (nth 3 (pos-visible-in-window-p desired-start nil t))))
> +                                 (and remaining-bottom (not (zerop remaining-bottom))))
> +                         (signal 'end-of-buffer nil)))
>                       (while (when-let ((posn (posn-at-point)))
> -                              (< (cdr (posn-x-y posn)) delta))
> +                              (and (< (point) (point-min))
> +                                   (< (cdr (posn-x-y posn)) delta)))
>                         (when (zerop (vertical-motion 1))
>                           (set-window-start nil desired-start)
>                           (signal 'end-of-buffer nil)))
>
> I am not sure it is the correct change since I don't understand the
> while loop but comparing 'point' and 'point-min' doesn't seem the write
> thing there. On the others hand if there is 'point-min' is 1 and
> 'point-max' 2, (cdr (posn-x-y posn))
>
> Po Lu <luangruo@yahoo.com> writes:
>
>> This is a known limitation of pixel-scroll-precision-mode: redisplay's
>> automatic recentering impededs adjustment of the vscroll as the image
>> moves outside of the window's text area.  Unfortunately, it's not slated
>> to be fixed any time soon.
>
> In this case it is not the recentering which is causing this problem,
> it is rather the binding for next-pos in
> pixel-scroll-precision-scroll-down-page which is the issue. The
> binding signals an error when downward vertical motion is not
> possible. However in this scenario scrolling can still be done.
> Replacing that binding with desired-start allow me to scroll the
> images.
>
> This change for example allows for scrolling tall images,
> @@ -524,10 +524,12 @@ pixel-scroll-precision-scroll-down-page
>           (next-pos (save-excursion
>                       (goto-char desired-start)
>                       (when (zerop (vertical-motion (1+ scroll-margin)))
> -                       (set-window-start nil desired-start)
> -                       (signal 'end-of-buffer nil))
> +                       (unless (let ((remaining-bottom (nth 3 (pos-visible-in-window-p desired-start nil t))))
> +                                 (and remaining-bottom (not (zerop remaining-bottom))))
> +                         (signal 'end-of-buffer nil)))
>                       (while (when-let ((posn (posn-at-point)))
> -                              (< (cdr (posn-x-y posn)) delta))
> +                              (and (< (point) (point-min))
> +                                   (< (cdr (posn-x-y posn)) delta)))
>                         (when (zerop (vertical-motion 1))
>                           (set-window-start nil desired-start)
>                           (signal 'end-of-buffer nil)))
>
> I am not sure it is the correct change since I don't understand the
> while loop but comparing 'point' and 'point-min' doesn't seem the write
> thing there. On the others hand if there is 'point-min' is 1 and
> 'point-max' 2, (cdr (posn-x-y posn)) is always zero, so that check makes
> the loop terminate without signaling an error.
>
> The behavior is also sub optimal in that it allows for scrolling past
> the lower edge of the image but how much depends on the speed of the
> scrolling, but that can be fixed easily.
>
> Rahguzar

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Rahguzar <rahguzar@zohomail.eu> writes:

>    (set-window-start nil desired-start)
> -                     

I tried to fix this differently on master.  Please see if it resolves
your problem (and other issues with scrolling past large images.)

As always, keep an eye out for performance regressions.  Thanks.

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Hi Po,

Po Lu <luangruo@yahoo.com> writes:

> I tried to fix this differently on master.  Please see if it resolves
> your problem (and other issues with scrolling past large images.)
>
> As always, keep an eye out for performance regressions.  Thanks.


The issue is still there and can be reproduced by evaluating

(let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
       (height (* (window-text-height win t) 2))
       (file "path/to/image"))
  (select-window win)
  (erase-buffer)
  (insert-image (create-image file nil nil))
  (goto-char 1)
  (pixel-scroll-precision-mode)
  nil)

The resulting image cannot be scrolled.

In the new code this is because vscroll is reset to 0 inside the binding
for `line-after`. Commenting out that line allows me to scroll the
image.

Rahguzar

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Rahguzar <rahguzar@zohomail.eu> writes:

> Hi Po,
>
> Po Lu <luangruo@yahoo.com> writes:
>
>> I tried to fix this differently on master.  Please see if it resolves
>> your problem (and other issues with scrolling past large images.)
>>
>> As always, keep an eye out for performance regressions.  Thanks.
>
>
> The issue is still there and can be reproduced by evaluating
>
> (let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
>        (height (* (window-text-height win t) 2))
>        (file "path/to/image"))
>   (select-window win)
>   (erase-buffer)
>   (insert-image (create-image file nil nil))
>   (goto-char 1)
>   (pixel-scroll-precision-mode)
>   nil)
>
> The resulting image cannot be scrolled.
>
> In the new code this is because vscroll is reset to 0 inside the binding
> for `line-after`. Commenting out that line allows me to scroll the
> image.

But as a repercussion, scrolling past the image will result in the
window being vscrolled indefinitely.  That is unacceptable, because
redisplay grows exponentially slower as vscroll increases.

Is this compromise acceptable?  It will enable scrolling within the last
line of the window, but will reset vscroll entirely once the window
start becomes invisible, resulting in a visually disconnected ``jump''
back to the top of that line.

diff --git a/lisp/pixel-scroll.el b/lisp/pixel-scroll.el
index 488f6781254..8961f196ec7 100644
--- a/lisp/pixel-scroll.el
+++ b/lisp/pixel-scroll.el
@@ -543,14 +543,18 @@ pixel-scroll-precision-scroll-down-page
         (let ((line-after (save-excursion
                             (goto-char new-start-position)
                             (if (zerop (vertical-motion 1))
-                                (progn
-                                  (set-window-vscroll nil 0 t t)
-                                  nil) ; nil means move to new-start-position.
+                                nil ; nil means move to new-start-position.
                               (point)))))
           (if (not line-after)
               (progn
                 (goto-char new-start-position)
-                (signal 'end-of-buffer nil))
+                ;; If vscroll has resulted in the entire line being
+                ;; scrolled outside the window's text area, set it to
+                ;; the height of the last line.
+                (let ((visibility (pos-visible-in-window-p new-start-position nil t)))
+                  (unless visibility
+                    (set-window-vscroll nil 0)
+                    (signal 'end-of-buffer nil))))
             (if (pos-visible-in-window-p line-after nil t)
                 (goto-char line-after)
               (goto-char new-start-position))))))))

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Hi Po,

Po Lu <luangruo@yahoo.com> writes:

> Rahguzar <rahguzar@zohomail.eu> writes:
>
>> Hi Po,
>>
>> Po Lu <luangruo@yahoo.com> writes:
>>
>>> I tried to fix this differently on master.  Please see if it resolves
>>> your problem (and other issues with scrolling past large images.)
>>>
>>> As always, keep an eye out for performance regressions.  Thanks.
>>
>>
>> The issue is still there and can be reproduced by evaluating
>>
>> (let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
>>        (height (* (window-text-height win t) 2))
>>        (file "path/to/image"))
>>   (select-window win)
>>   (erase-buffer)
>>   (insert-image (create-image file nil nil))
>>   (goto-char 1)
>>   (pixel-scroll-precision-mode)
>>   nil)
>>
>> The resulting image cannot be scrolled.
>>
>> In the new code this is because vscroll is reset to 0 inside the binding
>> for `line-after`. Commenting out that line allows me to scroll the
>> image.
>
> But as a repercussion, scrolling past the image will result in the
> window being vscrolled indefinitely.  That is unacceptable, because
> redisplay grows exponentially slower as vscroll increases.
>
> Is this compromise acceptable?  It will enable scrolling within the last
> line of the window, but will reset vscroll entirely once the window
> start becomes invisible, resulting in a visually disconnected ``jump''
> back to the top of that line.
>
> diff --git a/lisp/pixel-scroll.el b/lisp/pixel-scroll.el
> index 488f6781254..8961f196ec7 100644
> --- a/lisp/pixel-scroll.el
> +++ b/lisp/pixel-scroll.el
> @@ -543,14 +543,18 @@ pixel-scroll-precision-scroll-down-page
>          (let ((line-after (save-excursion
>                              (goto-char new-start-position)
>                              (if (zerop (vertical-motion 1))
> -                                (progn
> -                                  (set-window-vscroll nil 0 t t)
> -                                  nil) ; nil means move to new-start-position.
> +                                nil ; nil means move to new-start-position.
>                                (point)))))
>            (if (not line-after)
>                (progn
>                  (goto-char new-start-position)
> -                (signal 'end-of-buffer nil))
> +                ;; If vscroll has resulted in the entire line being
> +                ;; scrolled outside the window's text area, set it to
> +                ;; the height of the last line.
> +                (let ((visibility (pos-visible-in-window-p new-start-position nil t)))
> +                  (unless visibility
> +                    (set-window-vscroll nil 0)
> +                    (signal 'end-of-buffer nil))))
>              (if (pos-visible-in-window-p line-after nil t)
>                  (goto-char line-after)
>                (goto-char new-start-position))))))))


That is much better. Thank you!

I think even better would be to replace the

(set-window-vscroll nil 0)

with

(set-window-vscroll nil current-vs t t)

but that doesn't seem to work and the entire line scrolls out of view
which I agree is undesirable. I don't understand why it doesn't work.
Can you please explain why if possible?

Rahguzar

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Hi Po,

Po Lu <luangruo@yahoo.com> writes:

> Rahguzar <rahguzar@zohomail.eu> writes:
>
>> Hi Po,
>>
>> Po Lu <luangruo@yahoo.com> writes:
>>
>>> I tried to fix this differently on master.  Please see if it resolves
>>> your problem (and other issues with scrolling past large images.)
>>>
>>> As always, keep an eye out for performance regressions.  Thanks.
>>
>>
>> The issue is still there and can be reproduced by evaluating
>>
>> (let* ((win (display-buffer (get-buffer-create "image-pixel-precision-test")))
>>        (height (* (window-text-height win t) 2))
>>        (file "path/to/image"))
>>   (select-window win)
>>   (erase-buffer)
>>   (insert-image (create-image file nil nil))
>>   (goto-char 1)
>>   (pixel-scroll-precision-mode)
>>   nil)
>>
>> The resulting image cannot be scrolled.
>>
>> In the new code this is because vscroll is reset to 0 inside the binding
>> for `line-after`. Commenting out that line allows me to scroll the
>> image.
>
> But as a repercussion, scrolling past the image will result in the
> window being vscrolled indefinitely.  That is unacceptable, because
> redisplay grows exponentially slower as vscroll increases.
>
> Is this compromise acceptable?  It will enable scrolling within the last
> line of the window, but will reset vscroll entirely once the window
> start becomes invisible, resulting in a visually disconnected ``jump''
> back to the top of that line.
>
> diff --git a/lisp/pixel-scroll.el b/lisp/pixel-scroll.el
> index 488f6781254..8961f196ec7 100644
> --- a/lisp/pixel-scroll.el
> +++ b/lisp/pixel-scroll.el
> @@ -543,14 +543,18 @@ pixel-scroll-precision-scroll-down-page
>          (let ((line-after (save-excursion
>                              (goto-char new-start-position)
>                              (if (zerop (vertical-motion 1))
> -                                (progn
> -                                  (set-window-vscroll nil 0 t t)
> -                                  nil) ; nil means move to new-start-position.
> +                                nil ; nil means move to new-start-position.
>                                (point)))))
>            (if (not line-after)
>                (progn
>                  (goto-char new-start-position)
> -                (signal 'end-of-buffer nil))
> +                ;; If vscroll has resulted in the entire line being
> +                ;; scrolled outside the window's text area, set it to
> +                ;; the height of the last line.
> +                (let ((visibility (pos-visible-in-window-p new-start-position nil t)))
> +                  (unless visibility
> +                    (set-window-vscroll nil 0)
> +                    (signal 'end-of-buffer nil))))
>              (if (pos-visible-in-window-p line-after nil t)
>                  (goto-char line-after)
>                (goto-char new-start-position))))))))

This is just a ping. Any chance these changes will be part of Emacs
29.2? I think they are a big improvement over large images not scrolling
at all.

Thanks,
Rahguzar

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Rahguzar <rahguzar@zohomail.eu> writes:

> This is just a ping. Any chance these changes will be part of Emacs
> 29.2? I think they are a big improvement over large images not scrolling
> at all.

Alas no, by reason of our policy against risky behavioral changes to the
release branch.

I have asked several other users of p-s-p-m to comment on this offline,
but am still waiting for responses from some of them.

bug#65214: 29.1; Tall images in 'image-mode' can't be scrolled with 'pixel-scroll-precision-mode' on

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

Hi Po,

Po Lu <luangruo@yahoo.com> writes:

> Rahguzar <rahguzar@zohomail.eu> writes:
>
>> This is just a ping. Any chance these changes will be part of Emacs
>> 29.2? I think they are a big improvement over large images not scrolling
>> at all.
>
> Alas no, by reason of our policy against risky behavioral changes to the
> release branch.
>
> I have asked several other users of p-s-p-m to comment on this offline,
> but am still waiting for responses from some of them.

Makes sense, since the problem is in an edge case. Since it affects,
'image-mode' which is built in and also some modes which rely on the
functionality provided 'image-mode' is it possible to go with one of the
following workarounds:

1) Special case the handling of buffers with only one line. I don't know
if this can be made safe enough.

2) Modify the 'image-mode' to have a newline after the image. It seems
like a good enough solutions to me: as far as I can tell 'image-mode'
commands just care about the fact that point-min has the display
property holding the image. But most likely there are unintended
consequences I am not thinking of.

3) Have an easy way of disable 'pixel-scroll-precision-mode' buffer
locally. This can then be used by 'image-mode' and others modes. This
might be the best solution since 'image-mode' has sets its own
'mwheel-scroll-up/down-function' to keep track of 'vscroll' and
reapplies it when needed. As far as I can tell this bookkeeping can't be
done with 'pixel-scroll-precision-mode'. I think a non-default value for
'mwheel-scroll-up/down-function' is a good heuristic for when not to
enable 'pixel-scroll-precision-mode' in a buffer but that might also be
too broad a measure.

Or maybe some other way I am not thinking of.

Best,
Rahguzar