SDL2 OpenGL + Normal renderer example

main.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>

void init_opengl()
{
    glShadeModel( GL_SMOOTH );
    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
    glClearDepth( 1.0f );
    glEnable( GL_DEPTH_TEST );
    glDepthFunc( GL_LEQUAL );
    glHint( GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST );
}

void init_viewport(int width, int height)
{
    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, width, height, 0, -10, 10.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void render(SDL_Renderer *renderer, SDL_Texture *tex)
{
    SDL_RenderClear(renderer);
    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glLoadIdentity();

    glColor4f( 1.0f, 0.0f, 0.0f, 0.5f );
    glBegin( GL_TRIANGLES );
      glVertex3f(  0.0f,  100.0f, 1.0f );
      glVertex3f( 200.0f, 200.0f, 1.0f );
      glVertex3f(  100.0f, 200.0f, 1.0f );
    glEnd( );

    SDL_Rect dst;
    dst.x = 200;
    dst.y = 200;
    dst.w = 100;
    dst.h = 100;
    SDL_RenderCopyEx(renderer, tex, NULL, &dst, 0, NULL, 0);

    SDL_RenderPresent(renderer);
}

int main(int argc, char *argv[])
{
    SDL_Init(SDL_INIT_VIDEO);

    SDL_Window* window;
    SDL_Renderer* renderer;

    SDL_CreateWindowAndRenderer(800, 600, SDL_WINDOW_OPENGL, &window, &renderer);

    SDL_Surface *surface = SDL_CreateRGBSurface(0, 128, 128, 32, 0, 0, 0, 0);
    Uint32 blue = SDL_MapRGBA(surface->format, 0, 255, 0, 128);
    SDL_FillRect(surface, NULL, blue);
    SDL_Texture *tex = SDL_CreateTextureFromSurface(renderer, surface);
    SDL_FreeSurface(surface);

    init_opengl();
    init_viewport(800, 600);

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

      render(renderer, tex);
      SDL_Delay(1000);
    }

    SDL_DestroyTexture(tex);
    SDL_Quit();

    (void) argc;
    (void) argv;
    return 0;
}