CODEWITHSUNDEEP
c++.netvb.netopencv
Subodha Charles
Subodha Charles

Reputation: 81

Returning a Mat from C++ dll to VB.Net

I have written a function in C++ which takes a Mat class object and returns a Mat after processing. I want to integrate this to a UI written in VB.NET

I wrote this code segment in C++

extern "C" _declspec(dllexport) Mat cropImage(Mat matA){
     Mat matB = processingObject.doSomething(matA);
     return matB;
}

processingObject.doSomething(matA) works fine.

How Can I use this dll in VB? I don't mind changing the C++ code to make this work.

Thanks

Update >>>>

Found a workaround for the problem. Not 100% What I was looking for though

C++

extern "C" __declspec(dllexport) int* cropImage(char* path, int& size)
{
    Mat matA = pavObj.cropped_liquid_region(path);

    int rows = matA.rows;
    int cols = matA.cols;
    int channels = matA.channels();

    int length = rows*cols*channels + 3;
    size = length;
    int* arr = new int[length];

    arr[0] = rows;
    arr[1] = cols;
    arr[2] = channels;

    Mat layer[3];
    split(matA, layer); // split into color layers BGR
    int count = 3;

    for(int i=0;i<3;i++){
        for(int j=0;j<layer[i].rows;j++){
            for(int k=0;k<layer[i].cols;k++){
                arr[count] = layer[i].at<uchar>(j, k);
                count++;
            }
        }
    }

    return arr; 
}

extern "C" __declspec(dllexport) int ReleaseMemory(int* pArray)
{
    delete[] pArray;
    return 0;
}

VB Signatures

<DllImport("mat.dll", CallingConvention:=CallingConvention.Cdecl)> _
Public Shared Function cropImage(ByVal path As String, ByRef sz As Integer) As IntPtr
End Function

<DllImport("mat.dll", CallingConvention:=CallingConvention.Cdecl)> _
Public Shared Function ReleaseMemory(ByVal ptr As IntPtr) As Integer
End Function

VB call to dll

Dim size As Integer
Dim ptr As IntPtr = cropImage(path, size)
Dim result(size) As Integer
Marshal.Copy(ptr, result, 0, size)
ReleaseMemory(ptr)

So what basically happens is that the content of the image is taken to a 1D array and passed to the managed side where the image is reconstructed again.

Upvotes: 1

Views: 560

Answers (1)

Martin J.
Martin J.

Reputation: 5108

You need to use a DllImport call on the C# side to call your

http://msdn.microsoft.com/en-us/library/aa984739(v=vs.71).aspx
How to use <DllImport> in VB.NET?
http://www.codeproject.com/Articles/552348/C-23-2fCplusinteroppluswithplusDllImport

The gist of it is, you need to import your dll like this:

<System.Runtime.InteropService.DllImport("mat.dll", _
SetLastError:=True, CharSet:=CharSet.Auto)> _
<< VB Signature of your cropImage function >>

You will also probably need to do some parameter marshalling to "translate" your Mat type between VB and C++

Upvotes: 1

Related Questions