NtKinect: Kinect V2 C++ Programming with OpenCV on Windows10

How to make Kinect V2 face recognition as DLL and use it from Unity

2016.08.25: created by
2017.10.07: revised by
Japanese English
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Prerequisite knowledge

Creating Dynamic Link Library using Face Recognition with Kinect V2

In the article " NtKinect: How to make Kinect V2 program as DLL and use it from Unity ", it is explained how to create a DLL file that uses the basic functions of OpenCV and Kinect V2 via NtKinect, and use it from other programs and Unity.

Well, the programs that recognize face, speech and gesture with Kinect V2 require some additional DLL files corresponding to each function at execution time. Here, I will explain

how to make your own NtKinect program as a DLL, when the program uses the Kinect V2 function which needs some other DLLs and setting files,
How to use your NtKinect DLL from other languages/environments as C#/Unity, for example.

In this article, we will explain how to create a DLL file for face recognition.

How to write program

Let's craete a DLL library that perform face recognition as an example of Kinect V2 functions that actually requieres other DLLs and additional files.

  1. Start using the Visual Studio 2017's project KinectV2_dll.zip of "How to make Kinect V2 program as DLL and use it from Unity" .
  2. Configure settings for include files and libraries from project's properties.
    1. In the Solution Explorer, right-click over the project name and select "Properties" in the menu.

    2. Make settings at the state of Configuration: "All Configuration", Platform: "Acvive (x64)". By doing this, you can configure "Debug" and "Release" mode at the same time. Of course, you can change the settings separately.
    3. Add the face recognition library to link.
    4. "Configuration Properties" -> "Linker" -> "General" -> "Input"


  3. Write the declaration in the header file. The name of the header file is "ProjectName.h", which is "NtKinectDll.h" in this case.
  4. The magenta color part is the prototype declaration of the function added this time.

    #define NTKINECTDLL_API __declspec(dllexport)
    #define NTKINECTDLL_API __declspec(dllimport)
    extern "C" {
      NTKINECTDLL_API void* getKinect(void);
      NTKINECTDLL_API int faceDirection(void* ptr, float* dir);
  5. Write the definition in "ProjectName.cpp" which is "NtKinectDll.cpp" in this case.
  6. At first, define USE_FACE constant before including NtKinect.h. When you define USE_FACE, the program must be linked "Kinect20.Face.lib" library.

    Then, add the function definition of int faceDirection(void *, float *). In this function, the image acquired by the RGB camera is reduced to 1/16, and is displayed with cv::imshow(). On the image, the joints are drawn in red, and a cyan rectangle is drawn around the recognized face. Notice that calling cv::waitKey(1) is needed to display the OpenCV window properly. Since the direction of the face is three float values of pitch, yaw, and roll, and 6 people may be recognized, so the data area should be allocated more than "sizeof(float) * 3 * 6" bytes on the caller side. Return value is the number of recognized faces.

    #include "stdafx.h"
    #include "NtKinectDll.h"
    #define USE_FACE
    #include "NtKinect.h"
    using namespace std;
    NTKINECTDLL_API void* getKinect(void) {
      NtKinect* kinect = new NtKinect;
      return static_cast<void*>(kinect);
    NTKINECTDLL_API int faceDirection(void* ptr,float *dir) {
      NtKinect *kinect = static_cast<NtKinect*>(ptr);
      int scale = 4;
      cv::Mat img((*kinect).rgbImage);
      for (auto person: (*kinect).skeleton) {
        for (auto joint: person) {
          if (joint.TrackingState == TrackingState_NotTracked) continue;
          ColorSpacePoint cp;
          cv::rectangle(img, cv::Rect((int)cp.X/scale-2, (int)cp.Y/scale-2,4,4), cv::Scalar(0,0,255),2);
      for (auto r: (*kinect).faceRect) {
        cv::Rect r2(r.x/scale,r.y/scale,r.width/scale,r.height/scale);
        cv::rectangle(img, r2, cv::Scalar(255, 255, 0), 2);
      int idx=0;
      for (auto d: (*kinect).faceDirection) {
        dir[idx++] = d[0];
        dir[idx++] = d[1];
        dir[idx++] = d[2];
      return (*kinect).faceDirection.size();
  7. Build with "Application configuration" set to "Release". NtKinectDll.lib and NtKinectDll.dll are generated in the folder KinectV2_dll2/x64/Release/.
  8. [Caution](Oct/07/2017 added) If you encounter "dllimport ..." error when building with Visual Studio 2017 Update 2, please refer to here and deal with it to define NTKINECTDLL_EXPORTS in NtKinectDll.cpp.

  9. Please click here for this sample project NtKinectDll2.zip
  10. Since the above zip file may not include the latest "NtKinect.h", Download the latest version from here and replace old one with it.

Confirm the operation of the generated DLL file

Let's create a simple project to confirm that the generated DLL file works properly.

  1. Start using the Visual Studio 2017's project CheckDLL.zip of "How to make Kinect V2 program as DLL and use it from Unity" .
  2. Replace NtKinectDll.h in the project with a new one.
  3. Copy the new NtKinectDll.h onto the old NtKinectDll.h in the folder where the project source files as stdafx.cpp or CheckDLL.cpp are located.

  4. Replace the DLL and LIB file in the project's folder.
  5. Copy the new NtKinectDll.dll and NtKinectDll.lib onto the old ones the folder where the project source files as stdafx.cpp or CheckDLL.cpp are located.

  6. Copy the files related to face recognition to the project folder.
  7. Copy all the file under the $(KINECTSDK20_DIR)Redist\Face\x64\。 to the folder where the project source files as stdafx.cpp or CheckDLL.cpp are located. With the standard settings, $(KINECTSDK20_DIR) should be C:\Program Files\Microsoft SDKs\Kinect\v2.0_1409\ . ("V2.0_version number" depends on the version of SDK you are using).


  8. Change the contents of CheckDLL.cpp as follows.
  9. Allocate 18 float data to call faceDirection(void*,float*);.

    The second argument of the function is the data area for the face orientation up to 6 people.

    #include "stdafx.h"
    #include <iostream>
    #include <sstream>
    #include "NtKinectDll.h"
    using namespace std;
    int main() {
      void* kinect = getKinect();
      float dir[6*3];
      while (1) {
        int ret = faceDirection(kinect, dir);
        if (ret) {
          for (int i=0; i<ret; i++) {
    	cout << i << " pitch: " << dir[i*3+0] << "  "
    	     << "yaw: " << dir[i*3+1] << "  "
    	     << "roll: " << dir[i*3+2] << endl;
        } else {
          cout << "unknown" << endl;
      return 0;
  10. When you run the program, the recognized face directions are displayed on the console screen. Face can be recognized only when its skeleton is recognized. In the rightHandState() function of the DLL, Joints and faces are drawn with red and cyan squares on the RGB image, and the image is displayed in a window. You can see whether your skeleton and face is recognized or not by the window.

  11. Please click hre for this sample project CheckDLL2.zip

Use NtKinect DLL from Unity

Let's use NtKinectDll.dll in Unity.

  1. For more details on how to use DLL with Unity, please see the official manual .
  2. The data of Unity(C#) is managed and the data of DLL (C++) is unmanged. Managed means that the data is moved by the gabage collector. Unmanaged means that the data is not moved by the gabage collector. In order to pass data between C# and C++, it is necessary to convert the data state. To do this, the functions of System.Runtime.InteropServices.Marshal Class in C# can be used.
  3. For details on how to pass data between different languages, refer to the " Interop Marshaling " section of the " Interoperating with Unmanaged Code " at MSDN.
  4. Start a new Unity project.

  5. Copy NtKinectDll.h, NtKinectDll.lib, NtKinectDll.dll to the project folder Assets/Plugins/x86_64/ . And copy all the file under the $(KINECTSDK20_DIR)Redist\Face\x64\ to the project folder Assets/Plugins/x86_64/ .

  6. Place 6 Cubes in the scene, change their names as "Cube 0" to "Cube 5", and change their positions. You can leave the default position of the camera.
  7. From the upper menu, "Game Object"-> "3D Object" -> "Cube"

    Move the 6 Cubes as follows. There is no need to move the camera, since the camera views all the 6 Cubes from the default position.

    name Position Rotation Scale
    x y z x y z x y z
    Cube0 -5 0 0 0 0 0 1 1 1
    Cube1 -3 0 0 0 0 0 1 1 1
    Cube2 -1 0 0 0 0 0 1 1 1
    Cube3 1 0 0 0 0 0 1 1 1
    Cube4 3 0 0 0 0 0 1 1 1
    Cube5 5 0 0 0 0 0 1 1 1
    Main Camera 0 1 -10 0 0 0 1 1 1
  8. Place the Empty Object in the scene, and change its name to NtKinect.

  9. Create C# script under the Project's Assets/Scripts/
  10. From the top menu, "Assets"-> "Create" -> "C# Script" -> Filename is "NtKinectBehaviour"

    The pointers in C++ are treated as System.IntPtr in C#.

    using UnityEngine;
    using System.Collections;
    using System.Runtime.InteropServices;
    public class NtKinectBehaviour : MonoBehaviour {
        [DllImport ("NtKinectDll")] private static extern System.IntPtr getKinect();
        [DllImport ("NtKinectDll")] private static extern int rightHandState(System.IntPtr kinect);
        [DllImport ("NtKinectDll")] private static extern int faceDirection(System.IntPtr kinect, System.IntPtr data);
        private System.IntPtr kinect;
        int bodyCount = 6;
        GameObject[] obj;
        int counter;
        void Start () {
            kinect = getKinect();
    	obj = new GameObject[bodyCount];
    	obj[0] = GameObject.Find("Cube0");
    	obj[1] = GameObject.Find("Cube1");
    	obj[2] = GameObject.Find("Cube2");
    	obj[3] = GameObject.Find("Cube3");
    	obj[4] = GameObject.Find("Cube4");
    	obj[5] = GameObject.Find("Cube5");
        public static Quaternion ToQ (float pitch, float yaw, float roll) {
    	yaw *= Mathf.Deg2Rad;
    	pitch *= Mathf.Deg2Rad;
    	roll *= Mathf.Deg2Rad;
    	float rollOver2 = roll * 0.5f;
    	float sinRollOver2 = (float)System.Math.Sin ((double)rollOver2);
    	float cosRollOver2 = (float)System.Math.Cos ((double)rollOver2);
    	float pitchOver2 = pitch * 0.5f;
    	float sinPitchOver2 = (float)System.Math.Sin ((double)pitchOver2);
    	float cosPitchOver2 = (float)System.Math.Cos ((double)pitchOver2);
    	float yawOver2 = yaw * 0.5f;
    	float sinYawOver2 = (float)System.Math.Sin ((double)yawOver2);
    	float cosYawOver2 = (float)System.Math.Cos ((double)yawOver2);
    	Quaternion result;
    	result.w = cosYawOver2 * cosPitchOver2 * cosRollOver2 + sinYawOver2 * sinPitchOver2 * sinRollOver2;
    	result.x = cosYawOver2 * sinPitchOver2 * cosRollOver2 + sinYawOver2 * cosPitchOver2 * sinRollOver2;
    	result.y = sinYawOver2 * cosPitchOver2 * cosRollOver2 - cosYawOver2 * sinPitchOver2 * sinRollOver2;
    	result.z = cosYawOver2 * cosPitchOver2 * sinRollOver2 - sinYawOver2 * sinPitchOver2 * cosRollOver2;
    	return result;
        void Update () {
    	float[] data = new float[bodyCount * 3];
    	GCHandle gch = GCHandle.Alloc(data,GCHandleType.Pinned);
    	int n = faceDirection(kinect,gch.AddrOfPinnedObject());
    	counter = (n != 0) ? 10 : System.Math.Max(0,counter-1);
    	for (int i=0; i<bodyCount; i++) {
    	    if (i<n) {
    		obj[i].transform.rotation = ToQ(data[i*3+0],data[i*3+1],data[i*3+2]);
    		obj[i].GetComponent<Renderer>().material.color = new Color(1.0f,0.0f,0.0f,1.0f);
    	    } else if (counter == 0) {
    		obj[i].transform.rotation = Quaternion.identity;
    		obj[i].GetComponent<Renderer>().material.color = new Color(1.0f,1.0f,1.0f,1.0f);
  11. Add "NtKinectBehaviour.cs" script to "NtKinect" as a Component.

  12. When you run the program, as many cubes as the number of recognized faces turn red and rotate according to the face directions. Exit with 'q' key.
  13. Even if the face is being recognized, it often happens that face recognition fails momentaly. In such a case the cube moves severely and it is difficult to see, so we are doing a simple error handling to make tracking failure only when the recognition fails ten consecutive times (with the variable counter ). To handle correctly, we should receive faceTrackingId and judge for each face, but I keep it simple way to avoid complicated explanation code.

    [Notice] We generates an OpenCV window in DLL to display the skeleton recognition state. Note that when the OpenCV window is focused, that is, when the Unity game window is not focused, the screen of Unity will not change. Click on the top of Unity's window and make it focused, then try the program's behaviour.

  14. Please click here for this Unity sample project CheckNtKinectDll2.zip