elput: Fix synthetic relative motion events based on abs events

libinput won't actually give us this info, and logs an error instead.
We can't synthesize based on pointer position due to pointer
warping.

So we must track abs reports and use previous abs reports to
synthesize rel events.

src/lib/elput/elput_evdev.c

@@ -880,6 +880,23 @@ _pointer_motion_send(Elput_Device *edev)
    ecore_event_add(ECORE_EVENT_MOUSE_MOVE, ev, _event_free, ev->dev);
 }
 
+static void
+_pointer_motion_relative_fake(struct libinput_event_pointer *event, double dx, double dy)
+{
+   Elput_Event_Pointer_Motion *ev;
+
+   ev = calloc(1, sizeof(Elput_Event_Pointer_Motion));
+   EINA_SAFETY_ON_NULL_RETURN(ev);
+
+   ev->time_usec = libinput_event_pointer_get_time_usec(event);
+   ev->dx = dx;
+   ev->dy = dy;
+   ev->dx_unaccel = dx;
+   ev->dy_unaccel = dy;
+
+   ecore_event_add(ELPUT_EVENT_POINTER_MOTION, ev, NULL, NULL);
+}
+
 static void
 _pointer_motion_relative(struct libinput_event_pointer *event)
 {
@@ -937,6 +954,7 @@ _pointer_motion_abs(struct libinput_device *idev, struct libinput_event_pointer
 {
    Elput_Device *edev;
    Elput_Pointer *ptr;
+   double x, y;
 
    edev = libinput_device_get_user_data(idev);
    if (!edev) return EINA_FALSE;
@@ -944,16 +962,22 @@ _pointer_motion_abs(struct libinput_device *idev, struct libinput_event_pointer
    ptr = _evdev_pointer_get(edev->seat);
    if (!ptr) return EINA_FALSE;
 
-   ptr->seat->pointer.x =
+   x = edev->absx;
+   edev->absx =
      libinput_event_pointer_get_absolute_x_transformed(event, edev->ow);
-   ptr->seat->pointer.y =
+   ptr->seat->pointer.x = edev->absx;
+
+   y = edev->absy;
+   edev->absy =
      libinput_event_pointer_get_absolute_y_transformed(event, edev->oh);
+   ptr->seat->pointer.y = edev->absy;
+
    ptr->timestamp = libinput_event_pointer_get_time(event);
 
    /* TODO: these needs to run a matrix transform based on output */
 
    _pointer_motion_send(edev);
-   _pointer_motion_relative(event);
+   _pointer_motion_relative_fake(event, edev->absx - x, edev->absy - y);
 
    return EINA_TRUE;
 }

src/lib/elput/elput_private.h

@@ -231,6 +231,8 @@ struct _Elput_Device
 
    uint32_t ow, oh;
 
+   double absx, absy;
+
    const char *path;
    const char *output_name;
    struct libinput_device *device;