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OpenCV_API.m

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+%================================================================
+% This class abstracts the API to an external OpenCV library.
+% It implements static methods for updating the build information
+% at compile time and build time.
+
+classdef OpenCV_API < coder.ExternalDependency
+    %#codegen
+
+    methods (Static)
+
+        function bName = getDescriptiveName(~)
+            bName = 'OpenCV_API';
+        end
+
+        function tf = isSupportedContext(buildContext)
+            myTarget = {'mex','rtw'};% 验证代码生成目标为mex或者dll,lib,exe
+            if  buildContext.isCodeGenTarget(myTarget)
+                tf = true;
+            else
+                error('OpenCV_API only supported for mex, lib, exe, dll');
+            end
+
+            %             hw = buildContext.getHardwareImplementation();
+
+        end
+
+        function updateBuildInfo(buildInfo, buildContext)
+            % 输入buildInfo请参考：RTW.BuildInfo
+            % 输入buildContext请参考：coder.BuildConfig class
+            %
+            % Get file extensions for the current platform
+            %             [~, linkLibExt, execLibExt, ~] = buildContext.getStdLibInfo();
+
+            % Code to run on Linux platform
+            includeFilePath = fullfile("E:\opencv4_4_0\opencv\MinGW64_v8_OpenCV4_4_Contrib_install\include");
+            buildInfo.addIncludePaths(includeFilePath);
+
+            % Link files
+            libPath = fullfile("E:\opencv4_4_0\opencv\MinGW64_v8_OpenCV4_4_Contrib_install\x64\mingw\lib");
+            linkFiles = "libopencv_world440.dll.a";
+            linkPath = libPath;
+            linkPriority = "";
+            linkPrecompiled = true;
+            linkLinkOnly = true;
+            group = '';
+            buildInfo.addLinkObjects(linkFiles, linkPath, ...
+                linkPriority, linkPrecompiled, linkLinkOnly, group);
+
+            % include  and source path
+%             buildInfo.addIncludePaths("./");
+%             buildInfo.addSourcePaths("./");
+        end
+
+        %API for library function 'imread'
+        function outImg = imread(imagePath)
+            arguments
+                imagePath (1,1) string
+            end
+
+            outImg = coder.nullcopy(zeros(480,640,3,"uint8"));
+            if coder.target('MATLAB')
+                % running in MATLAB, use built-in addition
+                outImg = imread_opencv_mex(imagePath);
+            else
+                % Add the required include statements to the generated function code
+                coder.cinclude('opencvAPI.h');
+                % include external C++ functions
+                coder.updateBuildInfo('addSourceFiles', "opencvAPI.cpp");
+
+                % 调用OpenCV C++代码包装器
+                imgPath = [char(imagePath),0];
+                coder.ceval('imreadOpenCV', coder.rref(imgPath),coder.wref(outImg));
+            end
+        end
+    end
+end

README.md

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+# MATLAB MEX file For C/C++ code generation
+
+![logo](images/logo.PNG)
+
+## OverView
+
+In order to call external C/C++ library functions, it is generally recommended to use the [mex](https://ww2.mathworks.cn/help/matlab/ref/mex.html) built-in function to compile the source code into a mex executable file, but the disadvantage is that it is not easy to generate C/C++ code in turn if there are other matlab code mixed in. This example is just to show how to use [codegen](https://ww2.mathworks.cn/help/coder/ref/codegen.html) two-way through this process, not limited to the example itself, is a general method, another advantage is not limited to the code generation of various restrictions, fully integrated with C/C++ programming.
+
+## Requirements
+
+- MATLAB
+- Matlab Coder toolbox
+- [Supported and Compatible Compilers](https://ww2.mathworks.cn/en/support/requirements/supported-compilers.html)
+- Your External C/C++ Library(This example uses OpenCV as an example)
+
+## How to setup
+
+### 1.Configuring the compiler
+
+In the command window,configure your complier.
+
+```matlab
+mex -setup C++ 
+```
+
+### 2.Source Code Preparation
+
+Prepare your C/C++ code and MATLAB entry-point function.Prepare the implementation of the `updateBuildInfo(buildInfo, buildContext)` member function, rewritten according to the path of the external library. (header files and library files).
+
+### 3.Generate or Compile
+
+Generate or compile the files you want with the `codegen` command.
+For example:
+
+```matlab
+imagePath = "./test_480x640x3.jpg";
+input1 = coder.typeof(imagePath);
+input1.StringLength=inf;
+codegen -config:mex imread_opencv -args {input1}  -lang:c++ -report
+```

imread_opencv.m

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+function outImg = imread_opencv(imagePath)%#codegen
+% Brief: Write a function imreadOpencv that calls the external library function.
+% Details:
+%    Read a uint8 image of size 480*640
+%
+% Syntax:
+%     outImg = imread_opencv(imagePath)
+%
+% Inputs:
+%    imagePath - [1,1] size,[string] type,image path
+%
+% Outputs:
+%    outImg - [480,640] size,[uint8] type,Description
+%
+% codegen command:
+%    imagePath = "./test_480x640_uint8.jpg";
+%    input1 = coder.typeof(imagePath);
+%    input1.StringLength=inf;
+%
+%    codegen -config:mex imread_opencv -args {input1}  -lang:c++ -report
+%
+% Usage Example:
+%    imagePath = "./test_480x640_uint8.jpg";
+%    result = imread_opencv(imagePath);
+%
+%
+% Example:
+%    None
+%
+% See also: None
+
+
+arguments
+    imagePath (1,1) string
+end
+outImg = OpenCV_API.imread(imagePath);
+end

opencvAPI.cpp

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+#include "opencvAPI.h"
+
+// 对应OpenCV的cv::Mat转MATLAB uint8类型或logical图像
+void convertCVToMatrix(cv::Mat &srcImg, int rows, int cols, int channels, unsigned char dst[]) {
+    CV_Assert(srcImg.type() == CV_8UC1 || srcImg.type() == CV_8UC3);
+    size_t elems = rows * cols;
+    if (channels == 3) {
+        cv::Mat channels[3];
+        cv::split(srcImg.t(), channels);
+
+        memcpy(dst, channels[2].data, elems * sizeof(unsigned char));              //copy channel[2] to the red channel
+        memcpy(dst + elems, channels[1].data, elems * sizeof(unsigned char));      // green
+        memcpy(dst + 2 * elems, channels[0].data, elems * sizeof(unsigned char));  // blue
+    } else {
+        srcImg = srcImg.t();
+        memcpy(dst, srcImg.data, elems * sizeof(unsigned char));
+    }
+}
+
+
+void imreadOpenCV(const char *imagePath, unsigned char outImg[]) {
+    std::string imgPath(imagePath);
+    cv::Mat srcImg = cv::imread(imgPath, cv::IMREAD_COLOR);
+    if (srcImg.empty()) {
+        std::runtime_error("read image is empty!");
+    }
+
+    convertCVToMatrix(srcImg, srcImg.rows, srcImg.cols, srcImg.channels(), outImg);
+}

opencvAPI.h

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+
+#ifndef _OPENCVAPI_ALLPLATFORM_
+#define _OPENCVAPI_ALLPLATFORM_
+
+// base
+#include <iostream>
+#include <string>
+#include <fstream>
+#include <vector>
+
+// OpenCV
+#include <opencv2/core.hpp>
+#include <opencv2/imgcodecs.hpp>
+#include <opencv2/imgproc.hpp>
+
+
+// "marshalling"
+void convertCVToMatrix(cv::Mat &srcImg, int rows, int cols, int channels, unsigned char dst[]);
+
+void imreadOpenCV(const char *imagePath, unsigned char outImg[]);
+
+#endif