bug#67504: Pixel scroll down not smooth when scrolled horizontally

bug#67504: Pixel scroll down not smooth when scrolled horizontally

[Mattias Engdegård]

In pixel-scroll-precision-mode, when the buffer is scrolled horizontally, scrolling up is smooth but scrolling down is not. Smaller movements appear to get stuck without making progress.

Scrolling up or down is smooth when the buffer is not scrolled horizontally (ie, left margin is visible).

Observed in Emacs 29 and 30 on macOS, NS port, scrolling with trackpad.

bug#67504: Pixel scroll down not smooth when scrolled horizontally

[Stefan Kangas]

Mattias Engdegård <mattias.engdegard@gmail.com> writes:

> In pixel-scroll-precision-mode, when the buffer is scrolled horizontally, scrolling up is smooth but scrolling down is not. Smaller movements appear to get stuck without making progress.
>
> Scrolling up or down is smooth when the buffer is not scrolled horizontally (ie, left margin is visible).
>
> Observed in Emacs 29 and 30 on macOS, NS port, scrolling with trackpad.

Copying in Po Lu.

bug#67504: Pixel scroll down not smooth when scrolled horizontally

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

Stefan Kangas <stefankangas@gmail.com> writes:

> Mattias Engdegård <mattias.engdegard@gmail.com> writes:
>
>> In pixel-scroll-precision-mode, when the buffer is scrolled
>> horizontally, scrolling up is smooth but scrolling down is
>> not. Smaller movements appear to get stuck without making progress.
>>
>> Scrolling up or down is smooth when the buffer is not scrolled
>> horizontally (ie, left margin is visible).
>>
>> Observed in Emacs 29 and 30 on macOS, NS port, scrolling with
>> trackpad.
>
> Copying in Po Lu.

I thought I replied that this is user error: pixel scrolling to a
position that requires moving point will reset hscroll unless
auto-hscroll-mode is off, as it should be if moving point to the start
of a line is not meant to reset hscroll, whether through scrolling or
otherwise.

Thanks.

bug#67504: Pixel scroll down not smooth when scrolled horizontally

[Mattias Engdegård]

26 dec. 2023 kl. 02.38 skrev Po Lu <luangruo@yahoo.com>:

> pixel scrolling to a
> position that requires moving point will reset hscroll unless
> auto-hscroll-mode is off, as it should be if moving point to the start
> of a line is not meant to reset hscroll, whether through scrolling or
> otherwise.

No, the bug shows even if no point motion takes place.
Here is my attempt at detailed reproduction instructions:

1. Start Emacs. Switch to a new buffer.
2. C-u 100 a
3. C-u 200 M-x duplicate-dwim RET
4. If necessary, resize the frame so that the lines wrap.
5. C-x x t
6. M-x pixel-scroll-precision-mode RET
7. C-u 100 M-g g
8. C-l   (to center point on screen)
9. C-e

Now try scrolling gently up/down using the trackpad, mouse wheel or similar device.
Expected: buffer scrolls smoothly in both directions.
Observed: buffer scrolls smoothly in one direction but not the other.

It would be useful if someone would try reproducing this bug on platforms other than macOS as well, to help us understand if the bug is specific to that port.

> Thanks.

You are welcome.