C# Marshal / Pinvoke CBitmap?

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C# Marshal / Pinvoke CBitmap?

I cannot figure out how to marshal a C++ CBitmap to a C# Bitmap or Image class.

My import looks like this:

[DllImport(@"test.dll", CharSet = CharSet.Unicode)] public static extern IntPtr GetBitmap(System.IntPtr hwnd, int nBMPWIDTH, int nBMPHEIGHT);

The H file section looks like:

Cbitmap* GetBitmap（HWND hwnd,int nBMPWIDTH,int nBMPHEIGHT）；

How do I go about converting the Cbitmap into something I can display in C#?

Many thanks.

+1 A:

The closest API in the .NET Framework is Image.FromHbitmap, but this would require you to extract the HBITMAP from the CBitmap, which you can't do in C# (at least not without knowing the internals of CBitmap). If it's possible for you to modify your C++ GetBitmap function to return the HBITMAP rather than the CBitmap wrapper, that would be the easiest solution. Is that an option for you?

itowlson 2009-11-13 03:56:17

Seconded. You'll have to get the HBITMAP from the CBitmap, which you'll have to do in C++. You technically can marshal a class, but you'd have to know it's Exact memory layout.

shf301 2009-11-13 04:29:59

I do not have access to the c++ dll source. What can I do? Thank you.

Myakka 2009-11-14 01:08:29

Create a small C++ function as follows: HBITMAP GetHandle(CBitmap* pBitmap) { return (HBITMAP)( * pBitmap); }. Then P/Invoke this, passing your CBitmap IntPtr. The returned IntPtr is the HBITMAP. (The reason for still having the CBitmap * is so you can defer freeing it until you've finished with the HBITMAP; otherwise the CBitmap destructor will trash the handle for you I believe.)

itowlson 2009-11-14 01:40:45

Would I create this C++ function in managed CLR c++? or win32? Thank you.

Myakka 2009-11-14 22:17:02

I was thinking native C++. But you're probably right that it could also be done in C++/CLI, in which case you wouldn't need to P/Invoke the wrapper because it would be a .NET-to-.NET call (and the transition to native code would happen within your C++/CLI assembly).

itowlson 2009-11-14 22:43:58

Unfortunately I have no a access to the c++ dll source. Is there a way to do it in this case? I tried a memory stream without any luck. Thank you.

Myakka 2009-11-13 12:35:04

how you plan to delete the returning object? MFC's delete operator is not available in C#.

Sheng Jiang 蒋晟 2009-11-15 20:33:16

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C# Marshal / Pinvoke CBitmap?

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