code from the OpenGL serie of the Cherno

main.cpp

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

static
unsigned int compileShader(unsigned int type, const std::string& source)
{
    unsigned int id = glCreateShader(type);
    const char *s = source.c_str();
    glShaderSource(id, 1, &s, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE)
    {
        int len;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &len);
        char *msg = new char[len + 1];
        glGetShaderInfoLog(id, len, &len, msg);
        std::cout << msg << std::endl;
        delete msg;
        glDeleteShader(id);
        return 0;
    }
    return id;
}

static
unsigned int createShader(const std::string& vertexShader, const std::string& fragmentShader)
{
    unsigned int program = glCreateProgram();
    unsigned int vs = compileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = compileShader(GL_VERTEX_SHADER, fragmentShader);

    assert(vs != 0);
    assert(fs != 0);

    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    glDeleteShader(vs);
    glDeleteShader(fs);
    return program;
}

int main(void)
{
    GLFWwindow* window;

    if (!glfwInit())
        return 1;
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return 1;
    }
    glfwMakeContextCurrent(window);
    if (glewInit() != GLEW_OK)
    {
        std::cout << "Error" << std::endl;
        return 1;
    }
    std::cout << glGetString(GL_VERSION) << std::endl;

    float positions[6] = {
        -0.5f, -0.5f,
         0.0f,  0.5f,
         0.5f, -0.5f,
    };
    unsigned int buf;
    unsigned int i;
    glGenVertexArrays(1, &i);
    glBindVertexArray(i);
    glGenBuffers(1, &buf);
    glBindBuffer(GL_ARRAY_BUFFER, buf);
    glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);

    std::string vertexShader =
        "#version 330 core\n"
        "layout(location = 0) in vec4 position;\n"
        "void main()\n"
        "{\n"
        "   gl_Position = position;\n"
        "}\n";

    std::string fragmentShader =
        "#version 330 core\n"
        "layout(location = 0) out vec4 color;\n"
        "void main()\n"
        "{\n"
        "   color = vec4(1.0, 0.0, 0.0, 1.0);\n"
        "}\n";

    unsigned int shader = createShader(vertexShader, fragmentShader);
    glUseProgram(shader);

    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);
        // glDrawElements(GL_TRIANGLES, 3, 0

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glDeleteProgram(shader);
    glfwTerminate();
    return 0;
}