Create DLL using TrackerKCF for a Unity Project - Crash when updating the tracker with the DLL

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Hi guys !

I'd like to use some OpenCV Tracker's inside a Unity Project. To do so, I created a .dll file that I imported inside my unity project.

Here is my code to create the DLL :

cv::Ptr<cv::TrackerKCF> Tracker;
cv::Rect2d roi;

// To use image date from Unity
struct Color32
{
    uchar r;
    uchar g;
    uchar b;
    uchar a;
};

// To pass ROI's position information beetwen c# and c++
struct Square
{
    Square(int x, int y, int width, int height) : X(x), Y(y), Width(width), Height(height) {}
    int X, Y, Width, Height;
};

extern "C" bool __declspec(dllexport) __stdcall InitTracker(Color32* frameData, int cameraWidth, int cameraHeight, Square & square)
{
    Tracker = cv::TrackerKCF::create();
    cv::Mat frame(cameraHeight, cameraWidth, CV_8UC4, frameData);

    roi = selectROI("Selection", frame);
    square = Square(roi.x, roi.y, roi.width, roi.height);

    // return true if the init is OK, false otherwise
    bool success = Tracker->init(frame, roi);

    cv::rectangle(frame, roi, cv::Scalar(0, 0, 255));
    cv::imshow("Init", frame);

    return success;
}

extern "C" bool __declspec(dllexport) __stdcall UpdateTracker(Color32* frameData, int cameraWidth, int cameraHeight, Square & square)
{
    cv::Mat frame(cameraHeight, cameraWidth, CV_8UC4, frameData);
    cv::Mat copyToCheck(frame);

    cv::rectangle(copyToCheck, roi, cv::Scalar(0, 0, 255));
    cv::imshow("before Update", copyToCheck);
    cv::waitkey(0);

    bool success = Tracker->update(frame, roi);

    cv::rectangle(copyToCheck, roi, cv::Scalar(0, 0, 255));
    cv::imshow("after Uptade", copyToCheck);
    cv::waitkey(0);

    square = Square(roi.x, roi.y, roi.width, roi.height);
    return success;
}

extern "C" void __declspec(dllexport) __stdcall Close()
{
    cv::destroyAllWindows();
}

And here is my c# script :

using System;
using System.Runtime.InteropServices;

using Uk.Org.Adcock.Parallel;

using UnityEngine;

// Define the structure to be sequential and with the correct byte size (4 ints = 4 bytes * 4 = 16 bytes)
[StructLayout(LayoutKind.Sequential, Size = 16)]
public struct CvSquare
{
    public int X, Y, Width, Height;

    public CvSquare(int x, int y, int width, int height) : this()
    {
        this.X = x;
        this.Y = y;
        this.Width = width;
        this.Height = height;
    }
}

// To import the DLL's methods
internal static class TrackingCpp
{
    [DllImport("TrackingCppToDLL")]
    internal static extern void Close();

    [DllImport("TrackingCppToDLL")]
    internal static extern bool InitTracker(Color32[] frameData, int cameraWidth, int cameraHeight, ref CvSquare square);

    [DllImport("TrackingCppToDLL")]
    internal static extern bool UpdateTracker(Color32[] frameData, int cameraWidth, int cameraHeight, ref CvSquare square);
}

public class TrackingFromDLL : MonoBehaviour
{
    private Color32[] pixels32;
    private WebCamTexture _webcamTexture;
    private const int imWidth = 640;
    private const int imHeight = 480;
    private CvSquare square;

    void Start()
    {
        // initialized the webcam texture
        WebCamDevice[] devices = WebCamTexture.devices;
        _webcamTexture = new WebCamTexture(devices[0].name, imWidth, imHeight);

        // Play the video source
        _webcamTexture.Play();
    }

    void Update()
    {
        pixels32 = _webcamTexture.GetPixels32();
        int nbPixel = pixels32.Length;
        Color32[] reversePixels32 = new Color32[nbPixel];
        Parallel.For(0, imHeight, i =>
        {
            for (int j = 0; j < imWidth; ++j)
            {
                // OpenCV's pixel (0,0) is the top-left pixel
                int newPos = nbPixel - (i + 1) * imWidth + j;
                reversePixels32[newPos] = pixels32[i * imWidth + j];

                // OpenCV prefers BGRA instead of RBGA
                byte tmp = reversePixels32[newPos].b;
                reversePixels32[newPos].b = reversePixels32[newPos].r;
                reversePixels32[newPos].r = tmp;
            }
        });

        if (!isInitDone)
            isInitDone = TrackingCpp.InitTracker(reversePixels32 ...