Erratic mouse behavior in 12.04 [BUG IN XORG]

Marcelo Magno T. Sales mmtsales at gmail.com
Thu Jun 7 16:32:35 UTC 2012


Em terça-feira, 05 de junho de 2012, às 16:26:18, Basil Chupin escreveu:
> On 03/06/12 00:48, Marcelo Magno T. Sales wrote:
> > Em s�bado, 02 de junho de 2012, �s 16:40:26, Basil Chupin escreveu:
> >> On 31/05/12 03:40, Marcelo Magno T. Sales wrote:
> >> 
> >> [...........]
> >> 
> >>> It's not that I'm ignoring your suggestion, it's just that it's not so
> >>> simple to test it. Right now, Xorg can't even see the nvidia GPU. It is
> >>> "disabled", so to speak (not exactly, is on and consuming power, but
> >>> it's
> >>> invisible for the system). Only the Intel GPU is visible
> >> 
> >> Forgive me if I am misunderstanding something here...... but whatever
> >> graphic device you want to use is controlled by what you set it to be in
> >> your BIOS.
> >> 
> >> Are you saying that you have your BIOS set to use the Intel GPU on the
> >> motherboard?
> > 
> > No, unfortunately my BIOS does not have an option to set the GPU to be
> > used. I wish it had, it would be so much simpler to use the nvidia GPU...
> 
> [.........]
> 
> I am not ignoring what you wrote in what I have just trimmed and neither
> am I belabouring the point, but I find it most strange that your BIOS -
> even if it is on a Dell computer - not to have the ability to choose
> which video to use.
> 
> As far as I know - which is not much - your BIOS will show the standard
> options when you enter the BIOS settings (?CTRL-DEL? or does Dell use
> some other combination of keys?) but then if you press something like
> CTRL-Fx you will get additional options displayed. Have you tried this
> to see what those "hidden" options are?

Unfortunately, there is no hidden option in this BIOS either. I've tried every 
combination of keys I've seen in other BIOS, but no advanced options are 
shown. Dell's support also tells me there is no options other than those which 
are shown when you press F2 during the POST.
I also prefer to pick the components my self and build a custom computer if I 
can, but this system is an all-in-one and it's almost impossible to build such 
a system yourself, as it is with notebooks and laptops. Actually, it's body 
has much more in common with a laptop than with a desktop.

But I found the root of my pointing device problems. It is a bug in xorg, 
which is triggered when a coordinate transformation matrix is set using 
xinput:
https://bugs.freedesktop.org/show_bug.cgi?id=50664

I have to modify the default coordinate transformation matrix because I use 
two monitors, one above the other, and only the bottom one has a touchscreen.  
This is the one which is part of the Dell Inspiron One all-in-one system.
X defaults to map the touchscreen over the entire desktop and not over the 
area corresponding to the monitor which has the touchscreen, despite it being 
an absolute coordinates point device and not a relative coordinates one, like 
a mouse.
Because of that, the upper half of the touchscreen is mapped to the upper 
monitor, which does not have a touchscreen, and the bottom half is mapped to 
the bottom monitor. Of course, it is impossible to use the touchscreen with 
this mapping, because the cursor position in the desktop never corresponds to 
the actual position where I'm touching the screen, except in the bottom line 
of the desktop.
After I use xinput to restrict the area covered by the touchscreen device, X 
transforms the coordinates properly, ie, it now knows that the touchscreen 
covers only the bottom monitor and not the entire desktop. On the other hand, 
the button release events fail for the touchscreen (so it is not possible to 
click by tapping) and there are random jumps in the Y coordinate of the mouse 
cursor while the touchscreen is being used, and all sorts of strange problems 
start happening with the mouse buttons.
I guess I have to disable the touchscreen and wait until xorg is fixed or else 
change temporarily my configuration to clone mode when I want to use the 
touchscreen, so I don't have to modify the coordinate transformation matrix.

Thanks for all the help,

Marcelo




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