Unity中的C#与C++交互

参考：Unity Manual-Low-level Native Plugin Interface

源码demo
演示了一个渲染三角形的例子
C++部分代码实现了对底层API的封装以及核心功能实现。

RenderingPlugin.cpp中定义了C++的接口。其中定义了一系列全局变量，用户通过接口函数对这些全局变量赋值。如：
设定纹理

// --------------------------------------------------------------------------
// SetTextureFromUnity, an example function we export which is called by one of the scripts.

static void* g_TextureHandle = NULL;
static int   g_TextureWidth  = 0;
static int   g_TextureHeight = 0;

extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API SetTextureFromUnity(void* textureHandle, int w, int h)
{
    // A script calls this at initialization time; just remember the texture pointer here.
    // Will update texture pixels each frame from the plugin rendering event (texture update
    // needs to happen on the rendering thread).
    g_TextureHandle = textureHandle;
    g_TextureWidth = w;
    g_TextureHeight = h;
}

Plugin装载与卸载

static IUnityInterfaces* s_UnityInterfaces = NULL;
static IUnityGraphics* s_Graphics = NULL;

extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API UnityPluginLoad(IUnityInterfaces* unityInterfaces)
{
    s_UnityInterfaces = unityInterfaces;
    s_Graphics = s_UnityInterfaces->Get<IUnityGraphics>();
    s_Graphics->RegisterDeviceEventCallback(OnGraphicsDeviceEvent);

    // Run OnGraphicsDeviceEvent(initialize) manually on plugin load
    OnGraphicsDeviceEvent(kUnityGfxDeviceEventInitialize);
}

extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API UnityPluginUnload()
{
    s_Graphics->UnregisterDeviceEventCallback(OnGraphicsDeviceEvent);
}

渲染线程的回调函数

static void UNITY_INTERFACE_API OnRenderEvent(int eventID)
{
    // Unknown / unsupported graphics device type? Do nothing
    if (s_CurrentAPI == NULL)
        return;

    DrawColoredTriangle();
    ModifyTexturePixels();
    ModifyVertexBuffer();
}


// --------------------------------------------------------------------------
// GetRenderEventFunc, an example function we export which is used to get a rendering event callback function.

extern "C" UnityRenderingEvent UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API GetRenderEventFunc()
{
    return OnRenderEvent;
}

DrawColoredTriangle是渲染的处理函数，分别针对不同的底层API进行封装，如

RenderAPI_D3D11.cpp
RenderAPI_D3D12.cpp
RenderAPI_OpenGL2.cpp

C#为了调用plugin专门做一层封装，见UseRenderingPlugin.cs

引用dll中的方法

    // We'll also pass native pointer to a texture in Unity.
    // The plugin will fill texture data from native code.
#if (UNITY_IPHONE || UNITY_WEBGL) && !UNITY_EDITOR
    [DllImport ("__Internal")]
#else
    [DllImport ("RenderingPlugin")]
#endif
    private static extern void SetTextureFromUnity(System.IntPtr texture, int w, int h);

#if (UNITY_IPHONE || UNITY_WEBGL) && !UNITY_EDITOR
    [DllImport ("__Internal")]
#else
    [DllImport("RenderingPlugin")]
#endif
    private static extern IntPtr GetRenderEventFunc();

调用C++中的SetTextureFromUnity函数

    private void CreateTextureAndPassToPlugin()
    {
        // Create a texture
        Texture2D tex = new Texture2D(256,256,TextureFormat.ARGB32,false);
        // Set point filtering just so we can see the pixels clearly
        tex.filterMode = FilterMode.Point;
        // Call Apply() so it's actually uploaded to the GPU
        tex.Apply();

        // Set texture onto our material
        GetComponent<Renderer>().material.mainTexture = tex;

        // Pass texture pointer to the plugin
        SetTextureFromUnity (tex.GetNativeTexturePtr(), tex.width, tex.height);
    }

渲染线程注册C++的回调函数

private IEnumerator CallPluginAtEndOfFrames()
    {
        while (true) {
            // Wait until all frame rendering is done
            yield return new WaitForEndOfFrame();

            // Set time for the plugin
            SetTimeFromUnity (Time.timeSinceLevelLoad);

            // Issue a plugin event with arbitrary integer identifier.
            // The plugin can distinguish between different
            // things it needs to do based on this ID.
            // For our simple plugin, it does not matter which ID we pass here.
            GL.IssuePluginEvent(GetRenderEventFunc(), 1);
        }
    }