libweston: introduce notify_touch_normalized() and doc

notify_touch_normalized() is an extended form of notify_touch(), adding
normalized touch coordinates which are necessary for calibrating a
touchscreen.

It would be possible to invert the transformation and convert from
global coordinates to normalized device coordinates in input.c without
adding this API, but this way it is more robust against code changes.

Recovering normalized device coordinates is necessary because libinput
calibration matrix must be given in normalized units, and it would be
difficult to compute otherwise. Libinput API does not offer normalized
coordinates directly either, but those can be fetched by pretending the
output resolution is 1x1.

Anticipating touch calibration mode, the old notify_touch() is renamed
into a private process_touch_normal(), and the new
notify_touch_normalized() delegates to it.

Co-developed by Louis-Francis and Pekka.

v2:
- introduce struct weston_point2d_device_normalized
- rename notify_touch_cal() to notify_touch_normalized()
- remove WESTON_INVALID_TOUCH_COORDINATE

Cc: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
v1 Tested-by: Matt Hoosier <matt.hoosier@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

libweston/compositor.h

@@ -64,6 +64,12 @@ struct weston_transform {
 	struct wl_list link;
 };
 
+/** 2D device coordinates normalized to [0, 1] range */
+struct weston_point2d_device_normalized {
+	double x;
+	double y;
+};
+
 struct weston_surface;
 struct weston_buffer;
 struct shell_surface;
@@ -1543,8 +1549,24 @@ void
 notify_keyboard_focus_out(struct weston_seat *seat);
 
 void
+notify_touch_normalized(struct weston_touch_device *device,
+			const struct timespec *time,
+			int touch_id,
+			double x, double y,
+			const struct weston_point2d_device_normalized *norm,
+			int touch_type);
+
+/** Feed in touch down, motion, and up events, non-calibratable device.
+ *
+ * @sa notify_touch_cal
+ */
+static inline void
 notify_touch(struct weston_touch_device *device, const struct timespec *time,
-	     int touch_id, double x, double y, int touch_type);
+	     int touch_id, double x, double y, int touch_type)
+{
+	notify_touch_normalized(device, time, touch_id, x, y, NULL, touch_type);
+}
+
 void
 notify_touch_frame(struct weston_touch_device *device);
 

libweston/input.c

@@ -2338,17 +2338,10 @@ weston_touch_set_focus(struct weston_touch *touch, struct weston_view *view)
 	touch->focus = view;
 }
 
-/**
- * notify_touch - emulates button touches and notifies surfaces accordingly.
- *
- * It assumes always the correct cycle sequence until it gets here: touch_down
- * → touch_update → ... → touch_update → touch_end. The driver is responsible
- * for sending along such order.
- *
- */
-WL_EXPORT void
-notify_touch(struct weston_touch_device *device, const struct timespec *time,
-	     int touch_id, double double_x, double double_y, int touch_type)
+static void
+process_touch_normal(struct weston_touch_device *device,
+		     const struct timespec *time, int touch_id,
+		     double double_x, double double_y, int touch_type)
 {
 	struct weston_touch *touch = device->aggregate;
 	struct weston_touch_grab *grab = device->aggregate->grab;
@@ -2425,6 +2418,48 @@ notify_touch(struct weston_touch_device *device, const struct timespec *time,
 	}
 }
 
+/** Feed in touch down, motion, and up events, calibratable device.
+ *
+ * It assumes always the correct cycle sequence until it gets here: touch_down
+ * → touch_update → ... → touch_update → touch_end. The driver is responsible
+ * for sending along such order.
+ *
+ * \param device The physical device that generated the event.
+ * \param time The event timestamp.
+ * \param touch_id ID for the touch point of this event (multi-touch).
+ * \param double_x X coordinate in compositor global space.
+ * \param double_y Y coordinate in compositor global space.
+ * \param norm Normalized device X, Y coordinates in calibration space, or NULL.
+ * \param touch_type Either WL_TOUCH_DOWN, WL_TOUCH_UP, or WL_TOUCH_MOTION.
+ *
+ * Coordinates double_x and double_y are used for normal operation.
+ *
+ * Coordinates norm are only used for touch device calibration. If and only if
+ * the weston_touch_device does not support calibrating, norm must be NULL.
+ *
+ * The calibration space is the normalized coordinate space
+ * [0.0, 1.0]×[0.0, 1.0] of the weston_touch_device. This is assumed to
+ * map to the similar normalized coordinate space of the associated
+ * weston_output.
+ */
+WL_EXPORT void
+notify_touch_normalized(struct weston_touch_device *device,
+			const struct timespec *time,
+			int touch_id,
+			double x, double y,
+			const struct weston_point2d_device_normalized *norm,
+			int touch_type)
+{
+	if (touch_type != WL_TOUCH_UP) {
+		if (weston_touch_device_can_calibrate(device))
+			assert(norm != NULL);
+		else
+			assert(norm == NULL);
+	}
+
+	process_touch_normal(device, time, touch_id, x, y, touch_type);
+}
+
 WL_EXPORT void
 notify_touch_frame(struct weston_touch_device *device)
 {

libweston/libinput-device.c

@@ -419,6 +419,7 @@ handle_touch_with_coords(struct libinput_device *libinput_device,
 		libinput_device_get_user_data(libinput_device);
 	double x;
 	double y;
+	struct weston_point2d_device_normalized norm;
 	uint32_t width, height;
 	struct timespec time;
 	int32_t slot;
@@ -438,7 +439,14 @@ handle_touch_with_coords(struct libinput_device *libinput_device,
 	weston_output_transform_coordinate(device->output,
 					   x, y, &x, &y);
 
-	notify_touch(device->touch_device, &time, slot, x, y, touch_type);
+	if (weston_touch_device_can_calibrate(device->touch_device)) {
+		norm.x = libinput_event_touch_get_x_transformed(touch_event, 1);
+		norm.y = libinput_event_touch_get_y_transformed(touch_event, 1);
+		notify_touch_normalized(device->touch_device, &time, slot,
+					x, y, &norm, touch_type);
+	} else {
+		notify_touch(device->touch_device, &time, slot, x, y, touch_type);
+	}
 }
 
 static void