[PATCH libinput] tablet: invert tilt axes when left-handed is enabled

[Peter Hutterer]

On Mon, Dec 21, 2015 at 10:12:24AM -0800, Bill Spitzak wrote:
> I find it hard to believe this is what client programs will want.  A
> painting program wants the axis of an elongated brush to be perpendicular
> to the tilt will work correctly only if *both* axes are flipped (as your
> code appears to be doing). But it will get "which edge is nearer" backward
> if it wants to draw something asymmetric in the direction the pen is
> tilted. And it also seems to make little sense to flip the vertical tilt
> for a left-handed user.
> 
> Or are you perhaps undoing some flip that the tablet is doing internally?

a tablet in left-handed mode is effectively rotated by 180 degrees to bring
the set of buttons towards the side of the nondominant hand. this inverts x
and y, if we don't also invert tilt the client program will think that the
pen is tilted in the opposite direction. 

symmetrical tablets don't have a left-handed mode.

Cheers,
   Peter
 
> On Sun, Dec 20, 2015 at 5:46 PM, Peter Hutterer <peter.hutterer at who-t.net>
> wrote:
> 
> > Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> > ---
> >  src/evdev-tablet.c |  4 ++++
> >  test/tablet.c      | 38 ++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 42 insertions(+)
> >
> > diff --git a/src/evdev-tablet.c b/src/evdev-tablet.c
> > index bf61411..50891e3 100644
> > --- a/src/evdev-tablet.c
> > +++ b/src/evdev-tablet.c
> > @@ -365,6 +365,8 @@ tablet_handle_tilt(struct tablet_dispatch *tablet,
> >         if (bit_is_set(tablet->changed_axes, a)) {
> >                 absinfo = libevdev_get_abs_info(device->evdev, ABS_TILT_X);
> >                 tablet->axes[a] = normalize_tilt(absinfo);
> > +               if (device->left_handed.enabled)
> > +                       tablet->axes[a] *= -1;
> >         }
> >         tilt.x = tablet->axes[a];
> >
> > @@ -372,6 +374,8 @@ tablet_handle_tilt(struct tablet_dispatch *tablet,
> >         if (bit_is_set(tablet->changed_axes, a)) {
> >                 absinfo = libevdev_get_abs_info(device->evdev, ABS_TILT_Y);
> >                 tablet->axes[a] = normalize_tilt(absinfo);
> > +               if (device->left_handed.enabled)
> > +                       tablet->axes[a] *= -1;
> >         }
> >         tilt.y = tablet->axes[a];
> >
> > diff --git a/test/tablet.c b/test/tablet.c
> > index a55b60a..87af814 100644
> > --- a/test/tablet.c
> > +++ b/test/tablet.c
> > @@ -1018,6 +1018,43 @@ START_TEST(no_left_handed)
> >  }
> >  END_TEST
> >
> > +START_TEST(left_handed_tilt)
> > +{
> > +#if HAVE_LIBWACOM
> > +       struct litest_device *dev = litest_current_device();
> > +       struct libinput *li = dev->libinput;
> > +       struct libinput_event *event;
> > +       struct libinput_event_tablet_tool *tev;
> > +       enum libinput_config_status status;
> > +       struct axis_replacement axes[] = {
> > +               { ABS_DISTANCE, 10 },
> > +               { ABS_TILT_X, 90 },
> > +               { ABS_TILT_Y, 10 },
> > +               { -1, -1 }
> > +       };
> > +       double tx, ty;
> > +
> > +       status =
> > libinput_device_config_left_handed_set(dev->libinput_device, 1);
> > +       ck_assert_int_eq(status, LIBINPUT_CONFIG_STATUS_SUCCESS);
> > +
> > +       litest_drain_events(li);
> > +
> > +       litest_tablet_proximity_in(dev, 10, 10, axes);
> > +       libinput_dispatch(li);
> > +       event = libinput_get_event(li);
> > +       tev = litest_is_tablet_event(event,
> > +                                    LIBINPUT_EVENT_TABLET_TOOL_PROXIMITY);
> > +       tx = libinput_event_tablet_tool_get_tilt_x(tev);
> > +       ty = libinput_event_tablet_tool_get_tilt_y(tev);
> > +
> > +       ck_assert_double_lt(tx, 0);
> > +       ck_assert_double_gt(ty, 0);
> > +
> > +       libinput_event_destroy(event);
> > +#endif
> > +}
> > +END_TEST
> > +
> >  START_TEST(motion_event_state)
> >  {
> >         struct litest_device *dev = litest_current_device();
> > @@ -2852,6 +2889,7 @@ litest_setup_tests(void)
> >         litest_add("tablet:tilt", tilt_x, LITEST_TABLET|LITEST_TILT,
> > LITEST_ANY);
> >         litest_add("tablet:tilt", tilt_y, LITEST_TABLET|LITEST_TILT,
> > LITEST_ANY);
> >         litest_add_for_device("tablet:left_handed", left_handed,
> > LITEST_WACOM_INTUOS);
> > +       litest_add_for_device("tablet:left_handed", left_handed_tilt,
> > LITEST_WACOM_INTUOS);
> >         litest_add_for_device("tablet:left_handed", no_left_handed,
> > LITEST_WACOM_CINTIQ);
> >         litest_add("tablet:normalization", normalization, LITEST_TABLET,
> > LITEST_ANY);
> >         litest_add("tablet:pad", pad_buttons_ignored, LITEST_TABLET,
> > LITEST_ANY);
> > --
> > 2.5.0
> >
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> >