Create an SDL2 OpenGL 2 context

sdl_opengl_context_legacy.cpp

#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>
#include <GL/glu.h>
#include <stdio.h>

//compile g++ -Wall -Wextra -g -O3 -lGL -lGLU -lSDL2 main.cpp -o opengl_sdl

int main(int argc, char* args[])
{	
	SDL_GLContext context;
	const int screenWidth = 640;
	const int screenHeight = 480;
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);
	
	SDL_Window* window = SDL_CreateWindow( "SDL OpenGL", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, screenWidth, screenHeight, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN );
    
	SDL_GLContext myopengl_context = SDL_GL_CreateContext(window);

	if(myopengl_context == NULL) printf( "Error creating OpenGL context, SDL Error: %s\n", SDL_GetError());
	if(SDL_GL_SetSwapInterval(1)<0) printf( "Error setting vsync, SDL_error: %s\n", SDL_GetError());			

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glClearColor(0.0f,0.0f,0.0f,1.0f);

	bool running = true;
	SDL_Event event;
	while(running){
        while(SDL_PollEvent(&event)){
            if(event.type == SDL_QUIT){
                running = false;
            }
        }

        glClear(GL_COLOR_BUFFER_BIT);

        glBegin(GL_QUADS);
			glVertex2f( -0.5f, -0.5f );
			glVertex2f( 0.5f, -0.5f );
			glVertex2f( 0.5f, 0.5f );
			glVertex2f( -0.5f, 0.5f );
        glEnd();

        SDL_GL_SwapWindow(window);
    }

	SDL_DestroyWindow(window);
	window = nullptr;
	SDL_Quit();
	return 0;
}