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c#.netcomdirectxdirect3d

How to use D3D12GetDebugInterface API from c#?

I am currently trying to use Direct3D from c# and I've started by using the D3D12GetDebugInterface API. The C++ syntax of the function is as follows (copied from the Microsoft documentation):

HRESULT D3D12GetDebugInterface(
    REFIID riid,
    void   **ppvDebug
);

I'm having trouble importing the function into C#. I thought that maybe riid should be a pointer to a Guid struct, and I'm just using an IntPtr for **ppvDebug. Since **ppvDebug is a pointer to a pointer to an ID3D12Debug interface, I tried reimplementing the ID3D12Debug interface in C# code and using Marshal.PtrToStructure() to resolve the IntPtr to a usable ID3D12Debug interface instance, but that won't work. I remember reading about the ID3D12Debug interface being a COM object, but don't you need an ID for a COM object so you can import it? I haven't found any sort of COM ID anywhere in the documentation.

Anyway here's my latest attempt at getting something out of the function:

[DllImport("D3D12.dll")]
static extern int D3D12GetDebugInterface(IntPtr riid, IntPtr ppvDebug);

void func() {
    unsafe
    {
        IntPtr DebugControllerPtr = IntPtr.Zero;

        Type InterfaceType = typeof(ID3D12Debug);
        Guid ID = InterfaceType.GUID;
        IntPtr ptr = Marshal.AllocHGlobal(sizeof(Guid));
        Marshal.StructureToPtr(ID, ptr, false);

        D3D12GetDebugInterface(ptr, DebugControllerPtr);
        Marshal.FreeHGlobal(ptr);
        ID3D12Debug DebugController = null;
        Marshal.PtrToStructure(DebugControllerPtr, DebugController);
        DebugController.EnableDebugLayer();
    }
}

In case you want to see my ID3D12Debug interface:

interface ID3D12Debug
{
    void EnableDebugLayer();
}

As I said, I think Direct3D makes use of COM, which I am completely missing here, so maybe that's why it doesn't work.

Solution

  • There are usually many ways to declare interop code. Here is one that should work:

    public static void Main()
{
    D3D12GetDebugInterface(typeof(ID3D12Debug).GUID, out var obj);
    var debug = (ID3D12Debug)obj;
    debug.EnableDebugLayer(); // for example
}

[DllImport("D3D12")]
public static extern int D3D12GetDebugInterface([MarshalAs(UnmanagedType.LPStruct)] Guid riid, [MarshalAs(UnmanagedType.IUnknown)] out object ppvDebug);

[Guid("344488b7-6846-474b-b989-f027448245e0"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ID3D12Debug
{
    [PreserveSig]
    void EnableDebugLayer();
}