Touchscreen in DGA mode

SDL Development
1

Hello.

Sometime ago, Sam wrote:

The X server tends to provide mouse acceleration which isn’t present when
you’re using the DGA driver. In DGA mode, the X server sends raw mouse
events without doing any post-processing (to modify speed, etc.)

We could query the X server for the mouse acceleration options and use
those to modify the DGA mouse events…

Now I’m trying to use a MicroTouch pointer with SDL in DGA mode but i
get some weird behaviour, because the mouse works fine but when i put the
finger on the touchscreen the cursor it’s ok but he reports a wrong
position ! Then I want to know if there is someway to get this raw mouse
events data to check the x and y positions. The fullscreen and windowed
mode the mouse and the touchscreen work fine. Anybody out there use a
touchscreen in DGA mode with SDL ?

Thanks,
Jorge________________________________________________________________________________
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2

Now I’m trying to use a MicroTouch pointer with SDL in DGA mode but i
get some weird behaviour, because the mouse works fine but when i put the
finger on the touchscreen the cursor it’s ok but he reports a wrong
position ! Then I want to know if there is someway to get this raw mouse
events data to check the x and y positions. The fullscreen and windowed
mode the mouse and the touchscreen work fine. Anybody out there use a
touchscreen in DGA mode with SDL ?

I don’t think the DGA driver reports absolute mouse positions. I think
the X server is translating your motion into mouse deltas … but I’m not
sure about that.

See ya!
-Sam Lantinga, Software Engineer, Blizzard Entertainment

3

Now I’m trying to use a MicroTouch pointer with SDL in DGA mode but i
get some weird behaviour, because the mouse works fine but when i put
the

finger on the touchscreen the cursor it’s ok but he reports a wrong
position ! Then I want to know if there is someway to get this raw mouse
events data to check the x and y positions. The fullscreen and windowed
mode the mouse and the touchscreen work fine. Anybody out there use a
touchscreen in DGA mode with SDL ?

I don’t think the DGA driver reports absolute mouse positions. I think
the X server is translating your motion into mouse deltas … but I’m not
sure about that.

You’re correct. I have a little test program (‘dga.c’ from the XServer
sources)
using dga functions and i’ve seen this behaviour.

Then, it’s imposible to use a touchscreen in DGA mode as a mouse because i
don’t have a relative position when my finger is not over the touchscreen
only absolute positions.

Thanks,
Jorge

4

Hello,

It could be a little OT but is there some way to avoid getting mouse events
from SDL ?. If i have that the DGA mode send relative touchscreen/mouse
coordinates then i prefer to read the /dev/ttyS0 (touchscreen port)
directly
deactivating the XServer processing. But if i have in /etc/X11/XF86Config:

InputDevice “MousePS2” "CorePointer"
InputDevice “TouchMu” “SendCoreEvents”

i think that the XServer or some intermediate level eats the events because
i can get events from the serial port, but if i comment the second line the
events
are read fine. Anybody knows someway to deactive or unload the touchscreen
driver from the XServer in runtime and reload again later, using Xlib
functions
or SDL functions ?

Thanks,
Jorge