I would like to use the wheelEmulation for a touchscreen.
I have setup all the options:

Evdev Wheel Emulation (287):	1
	Evdev Wheel Emulation Axes (288):	0, 0, 4, 5
	Evdev Wheel Emulation Inertia (289):	10
	Evdev Wheel Emulation Timeout (290):	200
	Evdev Wheel Emulation Button (291):	1     // single touch touchscreen

Once activated, whenever I touched the screen even without moving I had the scroll to bottom. So I went to the code of driver : xf86-input-evdev-2.8.0

Here is what I pointed out :
/* We don't want to intercept real mouse wheel events */
         if(pEv->type == EV_ABS) {

             int axis = pEvdev->abs_axis_map[pEv->code];
             oldValue = valuator_mask_get(pEvdev->vals, axis);
                 xf86IDrvMsg(pInfo, X_WARNING, "oldValue : %d\n",oldValue);
             valuator_mask_set(pEvdev->vals, axis, value);
             value -= oldValue; /* make value into a differential
 measurement */
         }

 the oldValue is in my case always equals to zero, which make then the
 driver not working properly.

the pEvdev vals is reset here evdev.c line 1037:
   if (pEvdev->vals)
        valuator_mask_zero(pEvdev->vals);

so I commented theses lines. But then I get funny movements.
so I put the lines here emuWheels.c line 80
else {
            ms = pEvdev->emulateWheel.expires - GetTimeInMillis();
            if (ms > 0 || wheelDone == 0) {
                /*
                 * If the button is released early enough emit the button
                 * press/release events
                 */
                if (pEvdev->vals)
                        valuator_mask_zero(pEvdev->vals);

                EvdevQueueButtonClicks(pInfo, button, 1);
            }
        }
the funny movements were off. So far so good. But now in some cases, when I first touch the touchscreen I get some scroll down movements. 
So I did modify this (emuWheel.c):
        if(pEv->type == EV_ABS) {

            int axis = pEvdev->abs_axis_map[pEv->code];
            oldValue = valuator_mask_get(pEvdev->vals, axis);
                valuator_mask_set(pEvdev->vals, axis, value);
                if(oldValue==0 || (abs(oldValue-value))>200)
                {
                       
                        return TRUE;
                }
value -= oldValue; /* make value into a differential measurement */


and this (emuWheel.c):

    /* if this axis has not been configured, just eat the motion */
    if (!axis->up_button)
        return rc;
        xf86IDrvMsg(pInfo, X_WARNING, "axis->traveled_distance %d\n",axis->traveled_distance);
        if (axis->traveled_distance == 0 || (abs(value) < 10) )
        {
                axis->traveled_distance += value;
                return rc;
        }

    axis->traveled_distance += value;


then it seems to be ok for me. Except for slow movements that do not make scroll. and that the scroll is not smooth.

I did also something else, I wanted to have click on release even after the timeout of enable wheelEmulation. So even if the timeout is there , if there were no scroll activated then the button is clicked.  I added a global variable set when there is a scroll, and reset when button is pressed.


Kind regards,
Laurent.