Wheel / touchpad / trackpoint accuracy/speed scrolling fix for DrRacket

[Dexter Lagan]

  I started a new thread as the original topic no longer matched.

I installed 8.1.0.2 x64 CS and enabled logging in gen-wheels. Matt was right: wheel-steps-mode is indeed set to 'integer while gen-wheels runs in DrRacket's editor. The only two changes required to get smooth/accurate scrolling on touchpad gestures and trackpoint are therefore:

In share\pkgs\gui-lib\mred\private\wx\win32\window.rkt's gen-wheels private method:

(let loop ([amt (* wheel-scale amt)])

to

(let loop ([amt amt])

and reduce WHEEL_DELTA by a factor of 4, such as gen-wheels looks like:

  (define/private (gen-wheels w msg lParam amt down up)

    (define WHEEL_DELTA_S (/ WHEEL_DELTA 4))

    (let loop ([amt amt])

      (cond

        [((abs amt) . < . WHEEL_DELTA_S)

         (case wheel-steps-mode

           [(one integer) amt]

           [(fraction)

            (unless (zero? amt)

              (do-key w msg down lParam #f #f void (/ amt (exact->inexact WHEEL_DELTA_S))))

            0.0])]

        [(negative? amt)

         (case wheel-steps-mode

           [(one)

            (do-key w msg down lParam #f #f void 1.0)

            (loop (+ amt WHEEL_DELTA_S))]

           [(integer)

            (define steps (quotient (- amt) WHEEL_DELTA_S))

            (do-key w msg down lParam #f #f void (exact->inexact steps))

            (loop (+ amt (* steps WHEEL_DELTA_S)))]

           [else

            (do-key w msg down lParam #f #f void (/ (- amt) (exact->inexact WHEEL_DELTA_S)))

            0.0])]

        [else

         (case wheel-steps-mode

           [(one)

            (do-key w msg up lParam #f #f void 1.0)

            (loop (- amt WHEEL_DELTA_S))]

           [(integer)

            (define steps (quotient amt WHEEL_DELTA_S))

            (do-key w msg up lParam #f #f void (exact->inexact steps))

            (loop (- amt (* steps WHEEL_DELTA_S)))]

           [else

            (do-key w msg up lParam #f #f void (/ amt (exact->inexact WHEEL_DELTA_S)))

            0.0])])))

Happy Monday,

Dex

[Matthew Flatt]

Thanks for this summary! But I remain puzzled...

As I understand it, `wheel-scale` ends up being 4 on your machine. So
removing the multiplication by `wheel-scale` means that `amt` is 1/4 of
what it used to be. But `amt` is effectively always divided by
`WHEEL_DELTA`, which you've also divided by 4 in switching to
`WHEEL_DELTA_S`.

It seems like those factors of 1/4 would cancel out. Do the numbers
passed to `do-key` end up being different in some way that I'm missing?

Matthew

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[Dexter Lagan]

I’ll log the values at different spots and let you know what I find. Clearly, multiplying amt by wheel-scale affects the scrolling behaviour. Somehow this does not affect mouse wheel scrolling une same way. Either the scrolling changes when a different device is used, or the device driver itself changes the values and/or behaviour.

Dex

---

From: Matthew Flatt <mfl...@cs.utah.edu>
Sent: Thursday, April 15, 2021 1:49:49 PM
To: Dexter Lagan <dexte...@gmail.com>
Cc: Racket Users <racket...@googlegroups.com>
Subject: Re: [racket-users] Wheel / touchpad / trackpoint accuracy/speed scrolling fix for DrRacket

 

[Dexter Lagan]

Hi Matt,

  This works because when amt is smaller than WHEEL_DELTA, the amt value is used directly, see first branch of the cond :

        (cond

              [((abs amt) . < . WHEEL_DELTA_S)

               (case wheel-steps-mode

                 [(one integer) amt]

                 [(fraction)

                  (unless (zero? amt)

                    (do-key w msg down lParam #f #f void (/ amt (exact->inexact WHEEL_DELTA_S))))

                  0.0])]

  I logged the values with and without the fix. In both cases, I scrolled slowly down  :

WHEEL_DELTA_S:120

wheel-scale:4

amt:-8

WHEEL_DELTA_S:120

wheel-scale:4

amt:-40

WHEEL_DELTA_S:120

wheel-scale:4

amt:-168

WHEEL_DELTA_S:120

wheel-scale:4

amt:-48

WHEEL_DELTA_S:120

wheel-scale:4

amt:-200

WHEEL_DELTA_S:120

wheel-scale:4

amt:-80

WHEEL_DELTA_S:120

wheel-scale:4

amt:-332

WHEEL_DELTA_S:120

wheel-scale:4

amt:-92

WHEEL_DELTA_S:120

wheel-scale:4

amt:-376

  Amt is often larger than WHEEL_DELTA. After applying the changes (dividing WHEEL-DELTA and removing the wheel-scale mul) :

WHEEL_DELTA_S:30

wheel-scale:4

amt:-2

WHEEL_DELTA_S:30

wheel-scale:4

amt:-4

WHEEL_DELTA_S:30

wheel-scale:4

amt:-6

WHEEL_DELTA_S:30

wheel-scale:4

amt:-8

WHEEL_DELTA_S:30

wheel-scale:4

amt:-11

WHEEL_DELTA_S:30

wheel-scale:4

amt:-13

WHEEL_DELTA_S:30

wheel-scale:4

amt:-15

WHEEL_DELTA_S:30

wheel-scale:4

amt:-17

WHEEL_DELTA_S:30

wheel-scale:4

amt:-19

WHEEL_DELTA_S:30

wheel-scale:4

amt:-22

Amt is never above WHEEL_DELTA, which triggers only the first branch of the cond. The amt value is used with no adjustment, hense the precise behaviour.

Dex

[Matthew Flatt]

Oh, I think I finally get it.

The problem is that the leftover amount is returned by `gen-wheels`.
With scaling by `wheel-scale`, the returned leftover has been scaled
--- but when the leftover is passed back to `gen-wheels` later, it gets
scaled again.

Applying the scale to `WHEEL_DELTA` instead of `amt` solves the
problem, because then the returned leftover amount is on the same scale
as the argument amount.

Thanks for working through this, and I'll push this change!

At Fri, 16 Apr 2021 01:23:16 -0700 (PDT), Dexter Lagan wrote:
> Hi Matt,
>
> This works because when amt is smaller than WHEEL_DELTA, the amt value is
> used directly, see first branch of the cond :
>
> (cond

> * [((abs amt) . < . WHEEL_DELTA_S)*

> https://groups.google.com/d/msgid/racket-users/c604a711-b12d-4b82-bb17-819f2ab14
> 2d0n%40googlegroups.com.

[Dexter Lagan]

Yes! Thank you.

Dex

---

From: Matthew Flatt <mfl...@cs.utah.edu>
Sent: Friday, April 16, 2021 3:26:19 PM

To: Dexter Lagan <dexte...@gmail.com>
Cc: Racket Users <racket...@googlegroups.com>
Subject: Re: [racket-users] Wheel / touchpad / trackpoint accuracy/speed scrolling fix for DrRacket