Low-level native plug-in interface

Native Plug-ins in Unity can receive callbacks when certain events happen. You can use this to implement low-level rendering in your plug-in so it can work with Unity’s multithreaded rendering.

接口注册表

To handle main Unity events, a plug-in must export UnityPluginLoad and UnityPluginUnload functions. IUnityInterfaces enables the plug-in to access these functions, which you can find in IUnityInterface.h in the plug-in API:

# include "IUnityInterface.h"
# include "IUnityGraphics.h"
// Unity 插件加载事件
extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API
    UnityPluginLoad(IUnityInterfaces* unityInterfaces)
{
    IUnityGraphics* graphics = unityInterfaces->Get<IUnityGraphics>();
}

Access to the graphics device

Use the IUnityGraphics interface, which you can find in IUnityGraphics.h, to give a plug-in access to generic graphics device functionality. This script demonstrates how you can use the IUnityGraphics interface to register a callback:

#include "IUnityInterface.h"
#include "IUnityGraphics.h"
    
static IUnityInterfaces* s_UnityInterfaces = NULL;
static IUnityGraphics* s_Graphics = NULL;
static UnityGfxRenderer s_RendererType = kUnityGfxRendererNull;
    
// Unity plugin load event
extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API
    UnityPluginLoad(IUnityInterfaces* unityInterfaces)
{
    s_UnityInterfaces = unityInterfaces;
    s_Graphics = unityInterfaces->Get<IUnityGraphics>();
        
    s_Graphics->RegisterDeviceEventCallback(OnGraphicsDeviceEvent);
        
    // Run OnGraphicsDeviceEvent(initialize) manually on plugin load
    // to not miss the event in case the graphics device is already initialized
    OnGraphicsDeviceEvent(kUnityGfxDeviceEventInitialize);
}
    
// Unity plugin unload event
extern "C" void UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API
    UnityPluginUnload()
{
    s_Graphics->UnregisterDeviceEventCallback(OnGraphicsDeviceEvent);
}
    
static void UNITY_INTERFACE_API
    OnGraphicsDeviceEvent(UnityGfxDeviceEventType eventType)
{
    switch (eventType)
    {
        case kUnityGfxDeviceEventInitialize:
        {
            s_RendererType = s_Graphics->GetRenderer();
            //TODO: user initialization code on graphics device initialization. 
            For example, D3D11 resource creation.
            break;
        }
        case kUnityGfxDeviceEventShutdown:
        {
            s_RendererType = kUnityGfxRendererNull;
            //TODO: user graphics API code to call on graphics device shutdown.
            break;
        }
        case kUnityGfxDeviceEventBeforeReset:
        {
            //TODO: user graphics API code to call before graphics device reset.
            break;
        }
        case kUnityGfxDeviceEventAfterReset:
        {
            //TODO: user graphics API code to call after graphics device reset.
            break;
        }
    };
}

Plug-in callbacks on the rendering thread

You can use multithreading to render in Unity, if the platform and number of available CPUs allows for it.

Note: When you use multithreaded rendering, the rendering API commands happen on a thread that’s completely separate from the thread that runs MonoBehaviour scripts. The communication between the main thread and the render thread means that your plug-in might not start rendering immediately, depending on how much work the main thread has pushed to the render thread.

To render from the plug-in, call GL.IssuePluginEvent from your managed plug-in script. This causes Unity’s rendering pipeline to call the native function from the render thread, as demonstrated in the code example below. For example, if you call GL.IssuePluginEvent from the Camera’s OnPostRender function, the function will call a plug-in callback immediately after the camera has finished rendering.

Native plugin code:

// Plugin function to handle a specific rendering event
static void UNITY_INTERFACE_API OnRenderEvent(int eventID)
{
    // User rendering code
}
    
// Freely defined function to pass a callback to plugin-specific scripts
extern "C" UnityRenderingEvent UNITY_INTERFACE_EXPORT UNITY_INTERFACE_API
    GetRenderEventFunc()
{
    return OnRenderEvent;
}

Managed plug-in code:

#if UNITY_IPHONE && !UNITY_EDITOR
[DllImport ("__Internal")]
#else
[DllImport("RenderingPlugin")]
#endif
private static extern IntPtr GetRenderEventFunc();
    
// Queue a specific callback to be called on the render thread
GL.IssuePluginEvent(GetRenderEventFunc(), 1);

The signature for the UnityRenderingEvent callback is provided in IUnityGraphics.h in the Native Rendering Plugin sample.

使用 OpenGL 图形 API 的插件

There are two kinds of OpenGL objects:

• Objects shared across OpenGL contexts, such as texture, buffer, renderbuffer, samplers, query, shader, and program objects.
• Per-OpenGL context objects, such as vertex array, framebuffer, program pipeline, transform feedback, and sync objects.

Unity uses multiple OpenGL contexts. When initializing and closing the Editor and the Player, Unity relies on a master context, but when rendering it uses dedicated contexts. That is, you can’t create per-context objects during kUnityGfxDeviceEventInitialize and kUnityGfxDeviceEventShutdown events.