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.