Basic Procedure of Drawing Something in OpenGL 3.3

OpenGL330Basics.cpp

#include <gl/glew.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

GLuint vao;
GLuint vbo;
GLuint shader_program;
GLint uniform_color;
GLint uniform_MVP;

struct point {
    GLdouble x;
    GLdouble y;
};

void main() {
    //////////////// Create buffer objects ////////////////////
    glGenVertexArrays(1, &vao);
    glGenBuffers(1, &vbo);
    
    /////////////// Create shader program //////////////////////
    static const GLchar * vertex_shader_source[] = 
    {
        "#version 330 core                                                  \n"
        "                                                                   \n"
        "layout(location = 0) in vec2 position;                             \n"
        "                                                                   \n"
        "uniform mat4 MVP;                                                  \n"
        "                                                                   \n"
        "void main(){	                                                    \n"
        "   gl_Position =  MVP * vec4(position.xy, 0, 1);                   \n"
        "}                                                                  \n"
    }
    
    static const GLchar * fragment_shader_source[] = 
    {
        "#version 330 core                                                  \n"
        "                                                                   \n"
        "uniform vec4 vertexColor;                                          \n"
        "                                                                   \n"
        "out vec4 color;                                                    \n"
        "                                                                   \n"
        "void main(){	                                                    \n"
        "   color = vertexColor;                                            \n"
        "}                                                                  \n"
    }
    
    GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex_shader, 1, vertex_shader_source, NULL);
    glCompileShader(vertex_shader);
    
    GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER;
    glShaderSource(fragment_shader, 1, fragment_shader_source, NULL);
    glCompileShader(fragment_shader);
    
    shader_program = glCreateProgram();
    glAttachShader(shader_program, vertex_shader);
    glAttachShader(shader_program, fragment_shader);
    glLinkProgram(shader_program);
    
    glDeleteShader(vertex_shader);
    glDeleteShader(fragment_shader);
    
    glUseProgram(shader_program);
    uniform_MVP = glGetUniformLocation(shader_program, "MVP");
    uniform_color = glGetUniformLocation(shader_program, "vertexColor");
    
    /////////////// Set up data and automatic vertex attribute filling //////////////////// 
    static const point border[4] = {{-1.0f, -1.0f}, {1.0f, -1.0f}, {1.0f, 1.0f}, {-1.0f, 1.0f}};
    
    glBindVertexArray(vao);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(border), border, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 2, GL_DOUBLE, GL_FALSE, 0, (void*)0);
    
    /////////////// Send data to uniforms ///////////////////////////
    glm::mat4 MVP = glm::mat4(1.0f);
    MVP = glm::scale(MVP, glm::vec3(0.9f, 0.9f, 1.0f));
    glUniformMatrix4fv(uniform_MVP, 1, GL_FALSE, &MVP[0][0]);
    
    GLfloat color[4] = {1.0f, 0.0f, 0.0f, 1.0f}; // Red
    glUniform4fv(uniform_color, 1, color);
    
    /////////////// Finally draw! ///////////////////
    glDrawArrays(GL_LINE_LOOP, 0, 4);
    
    ////////////// Delete stuff after you're done ///////////////
    glDeleteBuffers(1, &vbo);
    glDeleteVertexArrays(1, &vao);
    
    glDeleteProgram(shader_program);
    
}