Question

How to draw a point in the middle of the screen using OpenGL with GLFW and GLEW in C++

Answer 1

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>

// Vertex Shader source code
const char* vertexShaderSource = R"(
#version 330 core
layout (location = 0) in vec3 aPos;
void main() {
    gl_Position = vec4(aPos, 1.0);
}
)";

// Fragment Shader source code
const char* fragmentShaderSource = R"(
#version 330 core
out vec4 FragColor;
void main() {
    FragColor = vec4(1.0, 1.0, 0.0, 1.0); // Yellow color
}
)";

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

int main() {
    // Initialize GLFW
    if (!glfwInit()) {
        std::cerr << "Failed to initialize GLFW - glfwInit()\n";
        return -1;
    }
    
    // Create a GLFW window
    GLFWwindow* window = glfwCreateWindow(800, 600, "OpenGL Point", nullptr, nullptr);
    if (!window) {
        std::cerr << "Failed to create GLFW window - glfwCreateWindow()\n";
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    
    // Initialize GLEW
    if (glewInit() != GLEW_OK) {
        std::cerr << "Failed to initialize GLEW - glewInit()\n";
        return -1;
    }
    
    // Build and compile the shader program
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr);
    glCompileShader(vertexShader);

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr);
    glCompileShader(fragmentShader);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // Set up vertex data and buffers
    float pointVertices[] = {
        0.0f, 0.0f, 0.0f // Coordinates of the point - center of the screen
    };

    GLuint VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(pointVertices), pointVertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    
    // Render loop
    while (!glfwWindowShouldClose(window)) {
        // Input - Press ESCAPE to exit
        if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
            glfwSetWindowShouldClose(window, true);

        // Render
        glClear(GL_COLOR_BUFFER_BIT);

        // Draw the point
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        glDrawArrays(GL_POINTS, 0, 1);

        // Swap buffers and poll events
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // Clean up
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);

    glfwDestroyWindow(window);
    glfwTerminate();

    return 0;
}


/*
run


*/

 

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