Implement evdev relative axis inversion

3 files changed, 22 insertions, 2 deletions

diff --git a/backends/evdev.c b/backends/evdev.c
index 565eb17..7a7913d 100644
--- a/backends/evdev.c
+++ b/backends/evdev.c
@@ -205,8 +205,13 @@ static int evdev_configure_instance(instance* inst, char* option, char* value) {
 			fprintf(stderr, "Failed to allocate memory\n");
 			return 1;
 		}
+		data->relative_axis[data->relative_axes].inverted = 0;
 		data->relative_axis[data->relative_axes].code = libevdev_event_code_from_name(EV_REL, option + 8);
-		data->relative_axis[data->relative_axes].max = strtoul(value, &next_token, 0);
+		data->relative_axis[data->relative_axes].max = strtoll(value, &next_token, 0);
+		if(data->relative_axis[data->relative_axes].max < 0){
+			data->relative_axis[data->relative_axes].max *= -1;
+			data->relative_axis[data->relative_axes].inverted = 1;
+		}
 		data->relative_axis[data->relative_axes].current = strtoul(next_token, NULL, 0);
 		if(data->relative_axis[data->relative_axes].code < 0){
 			fprintf(stderr, "Failed to configure relative axis extents for %s.%s\n", inst->name, option + 8);
@@ -313,6 +318,9 @@ static int evdev_push_event(instance* inst, evdev_instance_data* data, struct in
 			case EV_REL:
 				for(axis = 0; axis < data->relative_axes; axis++){
 					if(data->relative_axis[axis].code == event.code){
+						if(data->relative_axis[axis].inverted){
+							event.value *= -1;
+						}
 						data->relative_axis[axis].current = clamp(data->relative_axis[axis].current + event.value, data->relative_axis[axis].max, 0);
 						val.normalised = (double) data->relative_axis[axis].current / (double) data->relative_axis[axis].max;
 						break;
@@ -374,6 +382,11 @@ static int evdev_handle(size_t num, managed_fd* fds){
 				read_flags = LIBEVDEV_READ_FLAG_SYNC;
 			}
 
+			//exclude synchronization events
+			if(ev.type == EV_SYN){
+				continue;
+			}
+
 			//handle event
 			if(evdev_push_event(inst, data, ev)){
 				return 1;
diff --git a/backends/evdev.h b/backends/evdev.h
index d719631..f89e362 100644
--- a/backends/evdev.h
+++ b/backends/evdev.h
@@ -25,6 +25,7 @@ static int evdev_shutdown();
 #endif
 
 typedef struct /*_evdev_relative_axis_config*/ {
+	uint8_t inverted;
 	int code;
 	int64_t max;
 	int64_t current;
diff --git a/backends/evdev.md b/backends/evdev.md
index 995b44c..88dfc85 100644
--- a/backends/evdev.md
+++ b/backends/evdev.md
@@ -38,12 +38,18 @@ If an axis is not used for output, this configuration can be omitted.
 For real devices, all of these parameters for every axis can be found by running `evtest` on the device.
 
 To use the input from relative axes in absolute-value based protocols, the backend needs a reference frame to
-convert the relative movements to absolute values.
+convert the relative movements to absolute values. To invert the mapping of the relative axis, specify the `max` value
+as a negative number, for example:
+
+```
+relaxis.REL_X = -1024 512
+```
 
 If relative axes are used without specifying their extents, the channel will generate normalized values
 of `0`, `0.5` and `1` for any input less than, equal to and greater than `0`, respectively. As for output, only
 the values `-1`, `0` and `1` are generated for the same interval.
 
+
 #### Channel specification
 
 A channel is specified by its event type and event code, separated by `.`. For a complete list of event types and codes