SDL2 not creating triangle

Question

I tried to make a triangle, but it wont render when i compile and run the program.

Here is the code:

#include <iostream>
#include <gl/GL.h>
#include <SDL.h>
#include <SDL_opengl.h>

const int windowWidth = 1280, windowHeight = 720;

int main(int argc, char* argv[])
{
    // Create window //
    SDL_Window* window = SDL_CreateWindow("OpenGL Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, windowWidth, windowHeight, SDL_WINDOW_OPENGL);

    if (window == NULL)
    {
        return EXIT_FAILURE;
    }

    SDL_Event windowEvent;

    // OpenGL context //
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

    // Main loop //
    while (true)
    {
        if (SDL_PollEvent(&windowEvent))
        {
            if (windowEvent.type == SDL_QUIT)
            {
                break;
            }
        }
        // Draw //
        glClearColor(0.f, 0.f, 0.f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);

        glBegin(GL_TRIANGLES);
            glColor3f(1.f, 0.f, 0.f);
            glVertex2f(0, 0.5);
            glColor3f(0.f, 1.f, 0.f);
            glVertex2f(-0.5, -0.5);
            glColor3f(0.f, 0.f, 1.f);
            glVertex2f(0.5, -0.5);
        glEnd();

        glFlush();

        SDL_GL_SwapWindow(window);
    }

    SDL_DestroyWindow(window);
    SDL_Quit();

    return EXIT_SUCCESS;
}

Answer 1

Multiple issues:

• Call SDL_GL_SetAttribute()s before SDL_CreateWindow().
• Create a GL context with SDL_GL_CreateContext() before trying to call any GL functions.
• If you do end up using SDL_GL_CONTEXT_PROFILE_CORE you'll need to completely re-write the rest of your GL code to not use all those removed functions like glBegin()/glVertex()/glColor()/glEnd().

All together:

// g++ main.cpp `pkg-config --cflags --libs sdl2 gl`
#include <SDL.h>
#include <SDL_opengl.h>

int main(int argc, char* argv[])
{
    SDL_Window* window = SDL_CreateWindow("OpenGL Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, SDL_WINDOW_OPENGL);
    if (window == NULL)
    {
        return EXIT_FAILURE;
    }

    SDL_GLContext ctx = SDL_GL_CreateContext( window );

    // Main loop //
    while (true)
    {
        SDL_Event windowEvent;
        if (SDL_PollEvent(&windowEvent))
        {
            if (windowEvent.type == SDL_QUIT)
            {
                break;
            }
        }

        // Draw //
        glClearColor(0.f, 0.f, 0.f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);

        glBegin(GL_TRIANGLES);
            glColor3f(1.f, 0.f, 0.f);
            glVertex2f(0, 0.5);
            glColor3f(0.f, 1.f, 0.f);
            glVertex2f(-0.5, -0.5);
            glColor3f(0.f, 0.f, 1.f);
            glVertex2f(0.5, -0.5);
        glEnd();

        SDL_GL_SwapWindow(window);
    }

    SDL_GL_DeleteContext( ctx );
    SDL_DestroyWindow(window);
    SDL_Quit();

    return EXIT_SUCCESS;
}