evdev: add helper functions to convert between units and mm

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

2 files changed, 61 insertions, 0 deletions

diff --git a/src/evdev.h b/src/evdev.h
index d70dd34..f73b88b 100644
--- a/src/evdev.h
+++ b/src/evdev.h
@@ -537,4 +537,59 @@ evdev_libinput_context(const struct evdev_device *device)
 	return device->base.seat->libinput;
 }
 
+/**
+ * Convert the pair of coordinates in device space to mm. This takes the
+ * axis min into account, i.e. a unit of min is equivalent to 0 mm.
+ */
+static inline struct phys_coords
+evdev_device_units_to_mm(const struct evdev_device* device,
+			 const struct device_coords *units)
+{
+	struct phys_coords mm = { 0,  0 };
+	const struct input_absinfo *absx, *absy;
+
+	if (device->abs.absinfo_x == NULL ||
+	    device->abs.absinfo_y == NULL) {
+		log_bug_libinput(evdev_libinput_context(device),
+				 "%s: is not an abs device\n",
+				 device->devname);
+		return mm;
+	}
+
+	absx = device->abs.absinfo_x;
+	absy = device->abs.absinfo_y;
+
+	mm.x = (units->x - absx->minimum)/absx->resolution;
+	mm.y = (units->y - absy->minimum)/absy->resolution;
+
+	return mm;
+}
+
+/**
+ * Convert the pair of coordinates in mm to device units. This takes the
+ * axis min into account, i.e. 0 mm  is equivalent to the min.
+ */
+static inline struct device_coords
+evdev_device_mm_to_units(const struct evdev_device *device,
+			 const struct phys_coords *mm)
+{
+	struct device_coords units = { 0,  0 };
+	const struct input_absinfo *absx, *absy;
+
+	if (device->abs.absinfo_x == NULL ||
+	    device->abs.absinfo_y == NULL) {
+		log_bug_libinput(evdev_libinput_context(device),
+				 "%s: is not an abs device\n",
+				 device->devname);
+		return units;
+	}
+
+	absx = device->abs.absinfo_x;
+	absy = device->abs.absinfo_y;
+
+	units.x = mm->x * absx->resolution + absx->minimum;
+	units.y = mm->y * absy->resolution + absy->minimum;
+
+	return units;
+}
 #endif /* EVDEV_H */
diff --git a/src/libinput-private.h b/src/libinput-private.h
index 472f6f3..62576b5 100644
--- a/src/libinput-private.h
+++ b/src/libinput-private.h
@@ -82,6 +82,12 @@ struct threshold {
 	int lower;
 };
 
+/* A pair of coordinates in mm */
+struct phys_coords {
+	double x;
+	double y;
+};
+
 struct tablet_axes {
 	struct device_coords point;
 	struct normalized_coords delta;