Drawing A triangle with SDL2 and OpenGL - c++

Question

I am trying to make a game in C++ and using SDL2 with OpenGL.
When I try to draw a simple triangle to the opengl context with GLEW nothing is showing up. I haven't used opengl before.
Here is my code:
#define GLEW_STATIC
#include <GL/glew.h>
#include <GL/gl.h>
#include <SDL2/SDL.h>
#include <iostream>
I have Fragment and Vertex shaders but StackOverflow said I had too much code and not enough details.
int main(int argc, char *argv[])
{
SDL_Init(SDL_INIT_EVERYTHING);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
SDL_Window* window = SDL_CreateWindow("GAME", 100, 100, 800, 600, SDL_WINDOW_OPENGL);
SDL_GLContext context = SDL_GL_CreateContext(window);
glewExperimental = GL_TRUE;
glewInit();
GLuint vertexBuffer;
glGenBuffers(1, &vertexBuffer);
printf("%u\n", vertexBuffer);
float vertices[] = {
0.0f, 0.5f,
0.5f, -0.5f,
-0.5f, -0.5f
};
GLuint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER,vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexSource, NULL);
glCompileShader(vertexShader);
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
glCompileShader(fragmentShader);
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glBindFragDataLocation(shaderProgram, 0, "outColor");
glLinkProgram(shaderProgram);
glUseProgram(shaderProgram);
GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(posAttrib);
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
SDL_Event event;
while(true)
{
if (SDL_PollEvent(&event))
{
if(event.type == SDL_QUIT) break;
}
SDL_GL_SwapWindow(window);
glClearColor(0.2578125f, 0.52734375f, 0.95703125f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
}
SDL_GL_DeleteContext(context);
SDL_Quit();
return 0;
}
I compile this with g++ src/main.cpp glad/src/glad.c -I./glad/include -o main -lGL -lglfw -lGLEW -ldl -lSDL2 -ldl --std=c++14

Answer 1

The vertex specification is stored in the Vertex Array Object. glVertexAttribPointer and glEnableVertexAttribArray set states in the currently bound VAO. So you have to create and bind the VAO before the vertex specification.
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(posAttrib);