ABS_MT_POSITION_X and Y counted more than once when multi-touching

[Leslie Zhai]

Hi mtdev developers,

I use mtdev "read_mtdev.cpp" in the test.tar.bz2 to get ABS_MT_POSITION_X and ABS_MT_POSITION_Y sample "2s_zoom_in_sample.txt" for each ABS_MT_SLOT when multi-touching.

But ABS_MT_POSITION_X and Y counted more than once for each slot "sample_plot.cpp", the plot chart shown as "2slots_zoom_in.png".

When ./sample_plot 2s_zoom_in_sample.txt 0
to only show slot[0] as "slot0_zoom_in.png", there are three blue lines, but instead should be only one.

When ./sample_plot 2s_zoom_in_sample.txt 1
to only show slot[1] as "slot1_zoom_in.png", there are also three red lines, but instead should be only one too.

My question is whether or not I process the ABS_MT_POSITION_X and Y for EV_ABS motion event type in "m_process_absolute_motion_event" uncorrectly?
I read the source code "xf86-input-evdev" http://cgit.freedesktop.org/xorg/driver/xf86-input-evdev/tree/src/evdev.c
It mentioned that

MT axes are counted twice - once as ABS_X (which the kernel keeps for
backwards compatibility), once as ABS_MT_POSITION_X. So we need to keep a
mapping of those axes to make sure we only count them once

It means I have to filter or remove some _X and _Y from the sample ? HOWTO : other issue;

You can use scons http://www.scons.org to build the test case.
"sample_slot.cpp" use Vtk http://www.vtk.org to render plot chart, you might need to install libvtk.

[Leslie Zhai (xiangzhai83)]

Lenovo-IdeaPad-Yoga use protocol B
https://www.kernel.org/doc/Documentation/input/multi-touch-protocol.txt

so when ABS_MT_SLOT new contact packets received, ABS_MT_POSITION_X/Y cache should be clear.