Hello Triangle

Shaders

VBO

Vertex Attributes

#include <glad/glad.h> 
#include <GLFW/glfw3.h> 
#include <string>
#include <iostream>

// our size_callback function
void size_callback(GLFWwindow* window, int width, int height) {
    std::cout << "New width: " << width << "\theight: " << height << std::endl; 
    glViewport(0, 0, width, height);
}

int main() {
    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                    CREATE GLFW WINDOW                    <|
    // |>----------<>----------<>----------<>----------<>----------<|

    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);

    GLFWwindow* window = glfwCreateWindow(640, 480, "My 3D app", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return EXIT_FAILURE;
    }
    glfwMakeContextCurrent(window);

    glfwSetFramebufferSizeCallback(window, size_callback); // we bind callback to our size_callback func. 

    // |>----------<>----------<>----------<>----------<>----------<|
    // |>               LOAD OPENGL FUNCTION POINTERS              <|
    // |>----------<>----------<>----------<>----------<>----------<|

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        exit(EXIT_FAILURE);
    }



    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                      COMPILE SHADERS                     <|
    // |>----------<>----------<>----------<>----------<>----------<|

    const char* vertexShaderSource =
        "\n #version 330 core                                   "
        "\n                                                     "
        "\n layout (location = 0) in vec2 aPos;                 "
        "\n                                                     "
        "\n                                                     "
        "\n void main() {                                       "
        "\n    gl_Position = vec4(aPos.x, aPos.y, 0.0, 1.0);    "
        "\n }                                                   ";

    const char* fragmentShaderSource =
        "\n #version 330 core                                   "
        "\n                                                     "
        "\n out vec4 FragColor;                                 "
        "\n                                                     "
        "\n                                                     "
        "\n void main() {                                       "
        "\n    FragColor = vec4(0.9f, 0.2f, 0.2f, 1.0f);        "
        "\n }                                                   ";



    // build and compile our shader program
    // ------------------------------------


    // vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);

    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }



    // fragment shader
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }



    // link shaders to a program 
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }

    // delete shader after linking program because we dont need them 
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);



    //bind shader
    glUseProgram(shaderProgram);


    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                      DEFINE VERTICES                     <|
    // |>----------<>----------<>----------<>----------<>----------<|

    // We initialize a buffer on CPU
    float vertices[]{
        -0.5f, -0.5f, // 0
         0.0f,  0.5f, // 1
         0.5f, -0.5f  // 2
    };

    unsigned int VBO;
    glGenBuffers(1, &VBO); // Generate a buffer objet and assing it's ID to VBO variable 
    glBindBuffer(GL_ARRAY_BUFFER, VBO); // We connect/bind VBO to ARRAY_BUFFER
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); // create a new data store for a buffer object 
    // glBindBuffer: Specifies the target to which the buffer object is bound


    // we give meanings to our data. Because it is just a bunch of byte
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);





    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                       RENDER LOOP                        <|
    // |>----------<>----------<>----------<>----------<>----------<|

    while (!glfwWindowShouldClose(window)) {

        glClearColor(0.2f, 0.2f, 0.2f, 1.0f); // Background color -clear color- 
        glClear(GL_COLOR_BUFFER_BIT); // clear color of current buffer 

        // we draw a triangle
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

}

Refactor

main

#include <glad/glad.h> 
#include <GLFW/glfw3.h> 
#include <string>
#include <iostream>

#include "Shader.h"

void size_callback(GLFWwindow* window, int width, int height);
GLFWwindow* create_GLFWwindow();
void init_glad();


int main() {
    GLFWwindow* window = create_GLFWwindow();
    init_glad();

    Shader shader; 
    shader.compile();
    shader.bind();

    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                      DEFINE VERTICES                     <|
    // |>----------<>----------<>----------<>----------<>----------<|

    // We initialize a buffer on CPU
    float vertices[]{
        -0.5f, -0.5f, // 0
         0.0f,  0.5f, // 1
         0.5f, -0.5f  // 2
    };

    unsigned int VBO;
    glGenBuffers(1, &VBO); // Generate a buffer objet and assing it's ID to VBO variable 
    glBindBuffer(GL_ARRAY_BUFFER, VBO); // We connect/bind VBO to ARRAY_BUFFER
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); // create a new data store for a buffer object 
    // glBindBuffer: Specifies the target to which the buffer object is bound


    // we give meanings to our data. Because it is just a bunch of byte
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);



    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                       RENDER LOOP                        <|
    // |>----------<>----------<>----------<>----------<>----------<|

    while (!glfwWindowShouldClose(window)) {

        glClearColor(0.2f, 0.2f, 0.2f, 1.0f); // Background color -clear color- 
        glClear(GL_COLOR_BUFFER_BIT); // clear color of current buffer 

        // we draw a triangle
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

}



void size_callback(GLFWwindow* window, int width, int height) {
    std::cout << "New width: " << width << "\theight: " << height << std::endl;
    glViewport(0, 0, width, height);
}

GLFWwindow* create_GLFWwindow(){
    // |>----------<>----------<>----------<>----------<>----------<|
    // |>                    CREATE GLFW WINDOW                    <|
    // |>----------<>----------<>----------<>----------<>----------<|

    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);

    GLFWwindow* window = glfwCreateWindow(640, 480, "My 3D app", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        //return EXIT_FAILURE;
    }
    glfwMakeContextCurrent(window);

    glfwSetFramebufferSizeCallback(window, size_callback); // we bind callback to our size_callback func. 

    return window;
}

void init_glad(){
    // |>----------<>----------<>----------<>----------<>----------<|
    // |>               LOAD OPENGL FUNCTION POINTERS              <|
    // |>----------<>----------<>----------<>----------<>----------<|

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        exit(EXIT_FAILURE);
    }

}

Shader Class

#pragma once
#include <string>

class Shader
{
	unsigned int ID{};
	unsigned int compile_shader(std::string source, unsigned int shader_type);
	void compile_program(unsigned int vs, unsigned int fs);

public:
	void compile();
	void bind();
	void unbind();
};

#include "Shader.h"
#include "glad/glad.h"

#include <iostream>

void Shader::compile(){

    std::string vertexShaderSource =
        "\n #version 330 core                                   "
        "\n                                                     "
        "\n layout (location = 0) in vec2 aPos;                 "
        "\n                                                     "
        "\n                                                     "
        "\n void main() {                                       "
        "\n    gl_Position = vec4(aPos.x, aPos.y, 0.0, 1.0);    "
        "\n }                                                   ";

    std::string fragmentShaderSource =
        "\n #version 330 core                                   "
        "\n                                                     "
        "\n out vec4 FragColor;                                 "
        "\n                                                     "
        "\n                                                     "
        "\n void main() {                                       "
        "\n    FragColor = vec4(0.9f, 0.2f, 0.2f, 1.0f);        "
        "\n }                                                   ";

    unsigned int vs = compile_shader(vertexShaderSource, GL_VERTEX_SHADER);
    unsigned int fs = compile_shader(fragmentShaderSource, GL_FRAGMENT_SHADER);
    compile_program(vs, fs);
}

unsigned int Shader::compile_shader(std::string source, unsigned int shader_type)
{
    const char* source_code = source.c_str();
    unsigned int shaderID = glCreateShader(shader_type);
    glShaderSource(shaderID, 1, &source_code, NULL);
    glCompileShader(shaderID);

    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(shaderID, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(shaderID, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::" << (shader_type == GL_VERTEX_SHADER ? "VERTEX" : "FRAGMENT") << "::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    return shaderID;
}

void Shader::compile_program(unsigned int vs, unsigned int fs){
    // link shaders to a program 
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vs);
    glAttachShader(shaderProgram, fs);
    glLinkProgram(shaderProgram);

    // check for linking errors
    int success;
    char infoLog[512];
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }

    // delete shader after linking program because we dont need them 
    glDeleteShader(vs);
    glDeleteShader(fs);

    ID = shaderProgram;

}

void Shader::bind(){
    glUseProgram(ID);
}

void Shader::unbind(){
    glUseProgram(0);
}

https://www.khronos.org/opengl/wiki/Vertex_Specification