minimal example for bChanged issue since SteamVR 1.7.7

actions.cpp

// g++ actions.cpp -o actions -lopenvr_api

#include <stdio.h>
#include <openvr/openvr.h>

#include <chrono>
#include <thread>

using namespace vr;

void check_error(int line, EVRInitError error) { if (error != 0) printf("%d: error %s\n", line, VR_GetVRInitErrorAsSymbol(error)); }
void check_input_error(int line, EVRInputError error) { if (error != EVRInputError::VRInputError_None) {  printf("Input error at %d: %d\n", line, error); exit (1); } }

int main(int argc, char **argv) {
	if (argc < 2) {
		printf("Usage:\n\t%s /path/to/actions.json", argv[0]);
		return 1;
	}
	const char *manifest_path = argv[1];

	EVRInitError error;
	VR_Init(&error, vr::VRApplication_Overlay);
	check_error(__LINE__, error);

	EVRInputError inputerr = VRInput()->SetActionManifestPath(manifest_path);
    if (inputerr != EVRInputError::VRInputError_None) printf("Input error %d: %d\n", __LINE__, inputerr);

	VRActionSetHandle_t test_handle = 0;
	inputerr = VRInput()->GetActionSetHandle ("/actions/test", &test_handle);
	check_input_error(__LINE__, inputerr);

	VRActionHandle_t trigger_handle = 0;
	inputerr = VRInput()->GetActionHandle ("/actions/test/in/trigger", &trigger_handle);
	check_input_error(__LINE__, inputerr);

	VRActionSetHandle_t test2_handle = 0;
	inputerr = VRInput()->GetActionSetHandle ("/actions/test2", &test2_handle);
	check_input_error(__LINE__, inputerr);

	VRActionHandle_t pose_handle = 0;
	inputerr = VRInput()->GetActionHandle ("/actions/test2/in/hand_pose", &pose_handle);
	check_input_error(__LINE__, inputerr);

	VRInputValueHandle_t right_hand_handle = 0;
	inputerr =VRInput()->GetInputSourceHandle ("/user/hand/right", &right_hand_handle);
	check_input_error(__LINE__, inputerr);

	struct VRActiveActionSet_t active_test_action_set = {};
	active_test_action_set.ulActionSet = test_handle;

	struct VRActiveActionSet_t active_test2_action_set = {};
	active_test2_action_set.ulActionSet = test2_handle;
	while (true) {

		// polling the /actions/test2 set before the /actions/test makes data.bChanged below always false
		if (true) {
			inputerr = VRInput()->UpdateActionState(&active_test2_action_set, sizeof(active_test2_action_set), 1);
			check_input_error(__LINE__, inputerr);

			/*
			InputPoseActionData_t pose_data;
			inputerr = VRInput()->GetPoseActionDataRelativeToNow(pose_handle, TrackingUniverseStanding, 0, &pose_data, sizeof(pose_data), right_hand_handle);
			check_input_error(__LINE__, inputerr);
			*/
		}

		inputerr = VRInput()->UpdateActionState(&active_test_action_set, sizeof(active_test_action_set), 1);
		check_input_error(__LINE__, inputerr);

		InputDigitalActionData_t data;
		inputerr = VRInput()->GetDigitalActionData (trigger_handle, &data, sizeof(data), right_hand_handle);
		check_input_error(__LINE__, inputerr);
		printf("Right Trigger State: %d, Changed: %d\n", data.bState, data.bChanged);

		std::this_thread::sleep_for(std::chrono::milliseconds(100));
	}
	return 0;
}

actions.json

{
   "default_bindings":[
      {
         "controller_type":"vive_controller",
         "binding_url":"bindings_vive_controller.json"
      },
      {
        "controller_type": "knuckles",
        "binding_url": "bindings_vive_controller.json"
      }
   ],
   "actions":[
      {
         "name":"/actions/test/in/trigger",
         "type":"boolean"
      },
      {
        "name": "/actions/test2/in/hand_pose",
        "type": "pose"
      }
   ],
   "action_sets": [
      {
         "name": "/actions/test",
         "usage": "leftright"
      },
      {
         "name": "/actions/test2",
         "usage": "leftright"
      }
   ],
   "localization":[
      {
         "language_tag":"en_US",
         "/actions/test/in/trigger":"Trigger",
         "/actions/test2/in/hand_pose":"Hand Pose"
      }
   ]
}

bindings_vive_controller.json

{
   "bindings" : {
      "/actions/test" : {
         "sources" : [
            {
               "path": "/user/hand/right/input/trigger",
               "mode": "button",
               "inputs": {
                  "click": {
                     "output": "/actions/test/in/trigger"
                  }
               }
            },
            {
               "path": "/user/hand/left/input/trigger",
               "mode": "button",
               "inputs": {
                  "click": {
                     "output": "/actions/test/in/trigger"
                  }
               }
            },
            {
               "output": "/actions/test2/in/hand_pose",
               "path": "/user/hand/right/pose/raw"
            },
            {
               "output": "/actions/test2/in/hand_pose",
               "path": "/user/hand/left/pose/raw"
            }
         ]
      }
   },
   "controller_type": "vive_controller",
   "description" : "Test bindings",
   "name" : "Vive Controller"
}