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[Νίκος Αλεξανδρής <nikos.alexandris@xxxxxxxxxxxxxxxxxxxxxx>]

I cannot confirm this behaviour on the Macbook Pro 5,1 (currently using
Kubuntu 9.10/ 64-bit with mactel support). Scrolling with two fingers is
smooth here.

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Appletouch touchpad driver produces jumpy two-fingered scrolling
https://bugs.launchpad.net/bugs/381884
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Status in The Linux Kernel: New
Status in Mactel Support: New
Status in “xserver-xorg-input-synaptics” package in Ubuntu: Confirmed

Bug description:
Binary package hint: xserver-xorg-input-synaptics

My system is: Linux richard-laptop 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64 GNU/Linux.  However, this issue applies to at least Intrepid and Jaunty, 32 and 64 bit, running on Apple Mac hardware that uses an Appletouch touchpad.  It has also been reported in the Gentoo and Debian forums.

>From what I can find on the Net, the Appletouch touchpad was first used in February 2005 for the G4 aluminium PowerBook, and last used for the Macbook Pro in its 3rd generation, then 4th generation Intel Macbook in early 2008.

The issue is with two-fingered scrolling.  The Appletouch features the ability to detect two (or three) touches.  OS X uses this feature to enable scrolling, similar to a scrollwheel on a mouse.

The synaptics driver causes the simulated scrollwheel to start moving as soon as one places a second finger on the touchpad.  That is to say, placing a second finger causes the trackpad driver to deliver scrolling signals, which means that attempts at vertical scrolling feels jumpy, or over sensitive.

There was an update to the OS X driver that fixed this situation for Apple.  I guess that it detects the second finger and programmatically ignores the first few scrollticks, thereby 'deadening' the output.  This is what we need.

The synaptics driver allows for some modification, but not for multitouch input.  This needs to be fixed at source code level.

Richard