Re: [Emacs Master d277123f4bf] pixel-scroll-precision-scroll-up-page feels pause, but pixel-scroll-precision-scroll-down-page is smooth

[JD Smith <jdtsmith@gmail.com>]

> On Sep 3, 2024, at 9:13 PM, Po Lu <luangruo@yahoo.com> wrote:
> 
> JD Smith <jdtsmith@gmail.com> writes:
> 
>> Unfortunately this package only works on the Carbon emacs-mac port,
>> which exposes rich scroll events with pixel-level delta data.
> 
> Really?  Emacs has reported this data on all supported platforms since
> 29.1, as documented in (elisp)Misc Events. The interpolation
> implemented by pixel-scroll.el is not designed for events carrying this
> data but for those generated by mice.


Interesting, I actually hadn't seen those new wheel-up/down PIXEL-DELTA values.  They come straight from the system?

These are the mouse event properties delivered on Carbon emacs:

  ;; (nth 3 event) is a plist that may contain the following keys:
  ;; :direction-inverted-from-device-p		(boolean)
  ;; :delta-x, :delta-y, :delta-z		(floats)
  ;; :scrolling-delta-x, :scrolling-delta-y	(floats)
  ;; :phase, :momentum-phase			(symbols)
  ;;	possible value: `none', `began', `stationary', `changed',
  ;;			`ended', `cancelled', or `may-begin'
  ;; :swipe-tracking-from-scroll-events-enabled-p (boolean)

The key of interest is :scrolling-delta-y (a float), which taps directly into the system scroll amount, as configured in settings (with momentum, etc.).  I had the impression there was nothing equivalent in other emacs builds, and that was why pixel-scroll-precision has its own elisp-based "driver".  So all the momentum/interpolation code in pixel-scroll is effectively to allow low resolution mice to simulate high scroll event rate trackpads?  

Will take a closer look, thanks.