IL2CPP Back Coding

It is. When you put your C++ source code into Unity project, it gets compiled into the same DLL as IL2CPP generated C++ code (GameAssembly.dll).

To call it from generated Visual Studio project (which gets compiled into the ".exe" file), you'll have to mark the functions you want to call with "__declspec(dllexport)". Now, there are 2 ways to actually do the call:

1. Use LoadPackagedLibrary()/GetProcAddress() to dynamically fetch the function pointer for the desired function;
2. Add "$(OutDir)\GameAssembly.lib" to your linker settings in Visual Studio (like this), and just call it directly. Windows loader will load the function pointer for you.

 

Sure. But then you can only use the second option - GetProcAddress doesn't work nicely with classes.

Something like this:

Code (csharp):

1. #if GENERATED_PROJECT
2. #define PLUGIN_API __declspec(dllimport)
3. #else
4. #define PLUGIN_API __declspec(dllexport)
5. #endif
6.  
7. class PLUGIN_API MyClass
8. {
9. ....
10. };

And then in generated C++ project (let's say in MainPage.xaml.cpp), define "GENERATED_PROJECT" before including the header:

Code (csharp):

1. #define GENERATED_PROJECT 1
2. #include "..\Il2CppOutputProject\il2cppOutput\MyClass.h"

 

There are a couple of issues.

1. You cannot PInvoke into function pointers. You'll have to make an actual function in C++ code which you call from C#, which can then call your function pointer.

2. Don't include C++ files directly. That's a fast way to linker errors (even though it's not harmful in this case). Make a header file instead that has your function signatures and include that.

3. You'll have to annotate that function pointer with "PLUGIN_API" macro, or you will not be able to set it from a different binary.

 

Extern keywords for variables are only useful in header files. Also, for functions you call from C#, you need to mark them with extern "C" so the compile decorates their name accordingly. Lastly, the function you call from managed code needs to use __stdcall calling convention, as that's what managed code expects.

Do something like this:

In Plugin.h:

Code (csharp):

1. #if GENERATED_PROJECT
2. #define PLUGIN_API __declspec(dllimport)
3. #else
4. #define PLUGIN_API __declspec(dllexport)
5. #endif
6.  
7. extern PLUGIN_API void (*MyFunction)(int);

In Plugin.cpp:

Code (csharp):

1. #include "Plugin.h"
2.  
3. void (*MyFunction)(int);
4.  
5. extern "C" void __stdcall CallMyFunction(int number)
6. {
7.     MyFunction(number);
8. }

In Script.cs:

Code (csharp):

1. [DllImport("__Internal")]
2. private static extern void MyFunction(int number);
3.  
4. public void ButtonPressed()
5. {
6.     MyFunction(12);
7. }

In generated VS project any .cpp file:

Code (csharp):

1. #include "..\Il2CppOutputProject\il2cppOutput\Plugin.h"
2.  
3. void SetFunctionPointer()
4. {
5.     MyFunction = [](int a)
6.     {
7.          // do stuff with a
8.     };
9. }

I didn't actually test any of this, but it should work if I didn't make any syntax mistakes .

 

You can marshal delegates, but there are 2 restrictions:

1. They must point to a static method;
2. That method must be annotated with [MonoPInvokeCallback] attribute.

 

There's a good sample here:

https://forum.unity3d.com/threads/m...d-of-mono_runtime_invoke.295697/#post-1949374

 

Allocate it with AllocCoTaskMem on the C++ side, copy the characters in. Declare it as IntPtr in the P/Invoke signature to return it, then use Marshal.PtrToStringUni to extract the string and finally use Marshal.FreeCoTaskMem to free the allocated pointer.

 

Code (csharp):

1. [DllImport("__Internal")]
2. private static extern IntPtr GetString();
3.  
4. public static string GetStringFromNative()
5. {
6.     var stringPtr = GetString();
7.     var str = Marshal.PtrToStringUni(stringPtr);
8.     Marshal.FreeCoTaskMem(stringPtr);
9.     return str;
10. }

Code (csharp):

1. extern "C" wchar_t* GetString()
2. {
3.     const wchar_t* stringChars = ...; // the pointer to string characters
4.     const size_t stringLength = ...; // the length of string
5.  
6.     auto result = static_cast<wchar_t*>(AllocCoTaskMem(sizeof(wchar_t) * (stringLength + 1)));
7.     memcpy(result, stringChars, sizeof(wchar_t) * (stringLength + 1));
8.     return result;
9. }

 

See https://forum.unity.com/threads/uwp-get-swapchainpanel-grid-in-il2cpp-xaml-build.502176/