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This is my code for reading image from camera and display(With mirrored) with GLFW+OpenGL. May it help you.

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include "shader.h"
#include <iostream>
#include <opencv2/videoio.hpp>
#include <opencv2/imgproc.hpp>


using namespace cv;


void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow* window);
unsigned char* cvMat2TexInput(Mat& img);


int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // for Mac OSX
#endif

    VideoCapture cap(0);
    if (!cap.isOpened())
    {
        std::cout << "Camera not opened!" << std::endl;
        return -1;
    }
    Mat frame;
    cap >> frame;
    int width = frame.cols;
    int height = frame.rows;
    unsigned char* image = cvMat2TexInput(frame);

    // glfw window creation
    GLFWwindow* window = glfwCreateWindow(width, height, "frame", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }


    Shader ourShader("shader.vert", "shader.frag");
    float vertices[] = {
        //     Position       TexCoord
        -1.0f,  1.0f, 0.0f, 0.0f, 1.0f, // top left
        1.0f,   1.0f, 0.0f, 1.0f, 1.0f, // top right
        -1.0f, -1.0f, 0.0f, 0.0f, 0.0f, // below left
        1.0f,  -1.0f, 0.0f, 1.0f, 0.0f  // below right 
    };
    // Set up index
    unsigned int indices[] = {
        0, 1, 2,
        1, 2, 3
    };

    unsigned int VAO, VBO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);    
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), &vertices, GL_STATIC_DRAW);
    glGenBuffers(1, &EBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), &indices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);

    unsigned int texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    while(!glfwWindowShouldClose(window))
    {
        cap >> frame;
        image = cvMat2TexInput(frame);
        if(image)
        {
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
        }
        else
        {
            std::cout << "Failed to load texture." << std::endl;
        }

        processInput(window);
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        // Draw Rectangle
        ourShader.use();
        glBindTexture(GL_TEXTURE_2D, texture);
        glBindVertexArray(VAO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}


void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    (void)window;
    glViewport(0, 0, width, height);
}

void processInput(GLFWwindow* window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

unsigned char* cvMat2TexInput(Mat& img)
{
    cvtColor(img, img, COLOR_BGR2RGB);
    flip(img, img, -1);
    return img.data;
}