Passing a Handle to a Bitmap from a C++ DLL to a C# app using the Dll

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Passing a Handle to a Bitmap from a C++ DLL to a C# app using the Dll

Randy Feingersh 21

I'm trying to pass a handle to a bitmap from a non- CLI C++ Dll that I wrote to a C# app.

Sorry it's been a while and I could use some guidance on how to approach this. I"ve seen lost of stuff on passing Bitmaps from C# to non-CLI C++ dll but nothing going the other way.

Any suggestion will be much appreciated. I can modify the C++ Dll if need be.

Thanks

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Answer 1

Viorel 122.6K

If you have a HBITMAP, you can represent it as an IntPtr in C# and use Image.FromHBitmap to make an image object.

For example, you can define an exported function that returns HBITMAP. In C#, use [DllImport] attribute to access the external function. The return type will be IntPtr. It depends on details about your code.

Randy Feingersh 21 Reputation points

2021-02-03T21:54:06.117+00:00

Thanks!!
Very simple and much appreciated.
Randy Feingersh 21 Reputation points

2021-02-10T02:46:15.19+00:00

Using your suggestions I have now been successful in sending a handle to a Bitmap in my unmanaged C++ dll to the calling C# app.

But there is a memory leak each time the C# uses the Image.FromHBitmap even though the C++ unmanaged DLL Deletes the Bitmap Handle before allocating another one.
It would seem that the Bitmap needs to be deleted in the C# app but I don't know how to do that.

Thanks
prog 1 Reputation point

2022-04-14T02:12:13.703+00:00

It should be noted that the pixel format changes when converting to hbitmap.

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Passing a Handle to a Bitmap from a C++ DLL to a C# app using the Dll

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