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comp / comp.os.linux.misc / Re: Need Help With Libinput

SubjectAuthor
* Need Help With LibinputLester Thorpe
`* Re: Need Help With LibinputGerhard Strangar
 `- Re: Need Help With LibinputLester Thorpe

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Subject: Need Help With Libinput
From: Lester Thorpe
Newsgroups: alt.os.linux, comp.os.linux.misc
Organization: UsenetExpress - www.usenetexpress.com
Date: Tue, 2 Jul 2024 19:28 UTC
From: lt@gnu.rocks (Lester Thorpe)
Subject: Need Help With Libinput
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I desire a relatively slow pointing device (i.e. mouse) motion,
but with the now mandatory (i.e. no choice) libinput driver
under X Window I have a hard time understanding how to configure
the motion.

Using "xinput list" I discover that my pointing device is
device id=8.

Thus:

xinput list-props 8

....
....
Device 'PixArt Microsoft USB Optical Mouse':
Device Enabled (155): 1
Coordinate Transformation Matrix (157): 0.400000, 0.000000, 0.000000, 0.000000, 0.400000, 0.000000, 0.000000, 0.000000, 1.000000
....
....

The motion is apparently controlled by this "transformation
matrix," which seems to be 3x3 in size.

As seen above, I have what I assume to be the x and y motion
set to 0.4.

This does indeed slow the motion down.

But what do the rest of the values accomplish?

I can find no documentation on this issue. If someone can
provide links or a description it would be appreciated.

Subject: Re: Need Help With Libinput
From: Gerhard Strangar
Newsgroups: comp.os.linux.misc
Date: Wed, 3 Jul 2024 05:55 UTC
References: 1
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From: g.s@arcor.de (Gerhard Strangar)
Newsgroups: comp.os.linux.misc
Subject: Re: Need Help With Libinput
Date: Wed, 3 Jul 2024 05:55:40 +0000
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Lester Thorpe wrote:

> Coordinate Transformation Matrix (157): 0.400000, 0.000000, 0.000000, 0.000000, 0.400000, 0.000000, 0.000000, 0.000000, 1.000000
[...]
> But what do the rest of the values accomplish?
>
> I can find no documentation on this issue. If someone can
> provide links or a description it would be appreciated.

You cursor movement is the vector you get when you multiply the matrix
with the input vector:

/x'\ /x\
|y'| = M * |y|
\1 / \1/

The third dimension allows merging every possible transformation into a
single multiplication:

https://en.wikipedia.org/wiki/Affine_transformation#Image_transformation

Subject: Re: Need Help With Libinput
From: Lester Thorpe
Newsgroups: comp.os.linux.misc
Organization: UsenetExpress - www.usenetexpress.com
Date: Wed, 3 Jul 2024 19:41 UTC
References: 1 2
From: lt@gnu.rocks (Lester Thorpe)
Subject: Re: Need Help With Libinput
Newsgroups: comp.os.linux.misc
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On Wed, 3 Jul 2024 05:55:40 +0000, Gerhard Strangar wrote:

>
> You cursor movement is the vector you get when you multiply the matrix
> with the input vector:
>
> /x'\ /x\
> |y'| = M * |y|
> \1 / \1/
>

Great! Thanks!

These are essentially 2-D homogeneous coordinates.

Now that I know this I can experiment with different
settings and observe the effect via:

xinput --set-prop 8 ...

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