将C++ OpenCV的图像Mat传送到Unity3D并且渲染显示

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Unity3D中，我需要从C++的DLL中获取摄像头取得的图像数据(uchar *)，并且用Rawimage显示出来。

程序包括C++的DLL接口部分和Unity3D C#的接口部分。

使用VS 2015建立一个空白的Visual C++ Win32控制台应用程序，使用.NET Framework 4.7.2，应用程序类型为DLL。

C++ CameraDll.cpp:

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#include "Camera.h"

#define DLLExport __declspec(dllexport)

extern "C" {
	DLLExport Camera* CreateCamera(int width, int height, int fps) {
		Camera* obj = new Camera(width, height, fps);
		return obj;
	}

	DLLExport void DestroyCamera(Camera* obj) {
		delete obj;
		obj = NULL;
	}

	DLLExport bool GetImage(Camera* obj, unsigned char *& data, int &size) {
		return obj->GetImage(data, size);
	}
}

C++ Camera.cpp:

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...
bool Camera::GetImage(unsigned char*& rgb24_pixels, int& size) {
	...
	rgb24_pixels = img.data;
	size = img.cols * img.rows * img.channels();
	return true;
}
...

编译Release x64后，将dll文件放到Unity项目的Assets\Plugins文件夹中。Unity中建立Create Empty对象，添加一个脚本Camera.cs。

C# Camera.cs

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using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using UnityEngine;
using UnityEngine.UI;
using System.Runtime.InteropServices;

public class Camera : MonoBehaviour
{
    [DllImport("Camera")]
    private static extern IntPtr CreateCamera(int width, int height, int fps);

    [DllImport("Camera")]
    private static extern void DestroyCamera(IntPtr obj);

    [DllImport("Camera")]
    private static extern bool GetImage(IntPtr obj, ref IntPtr data, ref int size);
    
    private int width_ = 640;
    private int height_ = 480;
    private int fps_ = 30;
    
    private IntPtr Camera_ = IntPtr.Zero;
    private IntPtr data_ = IntPtr.Zero;
    private int size_ = 0;
    private byte[] buffer_ = null;

    private RawImage background_ = null;
    private Texture2D tex_ = null;

    // Start is called before the first frame update
    void Start()
    {
    	background_ = GameObject.FindWithTag("BackgroundImage").GetComponent<RawImage>(); 

    	Camera_ = CreateCamera(width_, height_, fps_);
    }

    void OnDestroy()
    {
    	if (Camera_ != IntPtr.Zero)
    	{
    		DestroyCamera(Camera_);
    		Camera_ = IntPtr.Zero;
    	}
    }

    // Update is called once per frame
    void Update()
    {
    	if (Camera_ == IntPtr.Zero) return;

    	bool flag = GetImage(Camera_, ref data_, ref size_);

    	if (!flag || size_ <= 0) return;

    	if (buffer_ == null) {
    		buffer_ = new byte[size_];
    	}

    	if (tex_ == null) {
    		tex_ = new Texture2D(width_, height_, TextureFormat.RGB24, false, false);
    	}

		System.Runtime.InteropServices.Marshal.Copy(data_, buffer_, 0, size_);
		tex_.LoadRawTextureData(buffer_);
		tex_.Apply();

		background_.texture = tex_;

		// byte[] bytes = tex_.EncodeToPNG();
		// File.WriteAllBytes("Image.png", bytes);
    }
}