Mixing DirectX headers with C mod project not working

Question

I'm trying to add a DirectX 11 renderer (not sure if that is even doable in a "simple" manner) to the Return To Castle Wolfenstein source code and I'm having some problems. I have a rendering class in a header that I included in the project, and whenever I include it in one of the RTCW files I get this error:

1>c:\program files (x86)\windows kits\8.1\include\um\directxmath.h(17): fatal error C1189: #error: DirectX Math requires C++

Now I am wondering what would be a way to use DirectX math functions/classes (and all DirectX classes actually) in a C project such as the RTCW code? Is it possible to change the entire project settings so it compiles as C++? I am using Visual Studio 2017.

This is my renderer class declaration in XD3D.h header:

#include <d3d11.h>
#include <DirectXMath.h>
#include "XGeomObject.h"
#include "XCamera.h"

using namespace DirectX; 

#define GPA(d3dModule, func) GetProcAddress(d3dModule, func)

class XD3DRenderer
{
protected:
    HMODULE                     m_XD3DModule;
    ID3D11Device*               m_pD3DDevice;
    ID3D11DeviceContext*        m_pDeviceContext;
    IDXGISwapChain*             m_pSwapChain;
    ID3D11RenderTargetView*     m_pRenderTargetView;
    ID3D11Texture2D*            m_pBackBuffer;
    ID3D11Texture2D*            m_pDepthStencilBuffer;
    ID3D11DepthStencilState*    m_pDepthStencilState;
    ID3D11DepthStencilState*    m_pDisabledDepthStencilState;
    ID3D11RasterizerState*      m_pRasterState;
    ID3D11DepthStencilView*     m_pDepthStencilView;

    HWND                        m_wnd;
    int                         m_screenWidth, m_screenHeight;
    bool                        m_fullScreen;
    D3DXMATRIX                  m_world, m_view, m_proj;
    bool                        m_lightMapsOn;

public:
    XD3DRenderer();
    XD3DRenderer(HWND wnd, int screenwidth, int screenheight,bool fullscreen);
    ~XD3DRenderer();

    ID3D11Device* GetD3DDevice() { return m_pD3DDevice; }
    ID3D11DeviceContext* GetDeviceContext() { return m_pDeviceContext; }

    bool LoadDriver();
    bool CreateD3DDevice(HWND wnd, int screenwidth, int screenheight, bool fullscreen );
    bool CreateRenderTargetView();
    bool CreateDepthBuffer();
    bool CreateDepthStencilView();
    bool CreateDisabledDepthStencilState();

    bool Setup();
    bool ClearScene(const D3DXCOLOR& col);
    bool Render(XGeomObject*, XCamera*);
    bool ShowScene();
    void TurnOnZBuffer();
    void TurnOffZBuffer();
};

And I include it in the C project in the RTCW win_glimp.c file like this:

#include <assert.h>
#include "../renderer/tr_local.h"
#include "../qcommon/qcommon.h"
#include "resource.h"
#include "glw_win.h"
#include "win_local.h"

#include "../renderer/XD3D.h"


extern void WG_CheckHardwareGamma( void );
extern void WG_RestoreGamma( void );

... rest of win_glimp.c file omitted.

Answer 1

The #error pragma is there because DirectXMath uses a bunch of C++ functionality that C doesn’t have.

Direct3D itself is a COM API and can be used that way via C, if you like (there are helpful macros for calling functions in many headers). But DirectXMath is not and cannot be used directly in C code. You could create a wrapper: write a C header that declares all the functions you need to use, implement them in a C++ source file that includes DirectXMath and is separately compiled as C++ (or a static library).

But you may be better off finding a C math library and saving yourself the trouble.

You could change the whole game project to compile as C++, but that may not work: if the project uses C features that don’t exist in C++, you’ll have to fix those errors instead. And the change may introduce subtle behavioral differences in places that may be hard to track down. It would not be my first choice for so large a codebase.

Answer 2

Well, I was able to find a math library that does not require C++. The D3DX (Direct3D 9) library does the same thing as the DirectXMath, basically.

d3dx9math.h is needed.

Reference:

https://msdn.microsoft.com/en-us/library/windows/desktop/bb147179(v=vs.85).aspx