tablet: add support for relative x/y motion deltas

Instead of an explicit tablet mode that device must be changed into, let the
caller decide which coordinates are preferred. The tablet mode may be
application-specific and usually depends on the tool as well.

This patch adds an interface to get a motion delta for the x/y axes in
pixel-like coordinates. libinput provides some magic to convert the tablet
data into something that resembles pixels from a mouse motion.
For unaccelerated relative motion, the caller should use the mm values from
the tablet and calculate deltas manually.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Jason Gerecke <jason.gerecke@wacom.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/src/libinput.h b/src/libinput.h
index 1cf690b..500224d 100644
--- a/src/libinput.h
+++ b/src/libinput.h
@@ -1583,6 +1583,40 @@ libinput_event_tablet_tool_get_y(struct libinput_event_tablet_tool *event);
 /**
  * @ingroup event_tablet
  *
+ * Return the delta between the last event and the current event.
+ * If the tool employs pointer acceleration, the delta returned by this
+ * function is the accelerated delta.
+ *
+ * This value is in screen coordinate space, the delta is to be interpreted
+ * like the return value of libinput_event_pointer_get_dx().
+ * See @ref tablet-relative-motion for more details.
+ *
+ * @param event The libinput tablet event
+ * @return The relative x movement since the last event
+ */
+double
+libinput_event_tablet_tool_get_dx(struct libinput_event_tablet_tool *event);
+
+/**
+ * @ingroup event_tablet
+ *
+ * Return the delta between the last event and the current event.
+ * If the tool employs pointer acceleration, the delta returned by this
+ * function is the accelerated delta.
+ *
+ * This value is in screen coordinate space, the delta is to be interpreted
+ * like the return value of libinput_event_pointer_get_dx().
+ * See @ref tablet-relative-motion for more details.
+ *
+ * @param event The libinput tablet event
+ * @return The relative y movement since the last event
+ */
+double
+libinput_event_tablet_tool_get_dy(struct libinput_event_tablet_tool *event);
+
+/**
+ * @ingroup event_tablet
+ *
  * Returns the current pressure being applied on the tool in use, normalized
  * to the range [0, 1].
  *