SDL2 with OpenGL for 3D (OpenGL with "windowing" requires SDL2 (or SDL1) or e.g. freeGLUT (GLUT implementation) )

sdl2-gl.c

// sdl2-gl.c (filename)
// SDL2 with OpenGL for 3D (OpenGL with "windowing" requires SDL2 (or SDL1) or e.g. freeGLUT (GLUT implementation) )

/* gcc sdl2-gl.c `sdl2-config --cflags --libs` -lopengl32 -lglu32 && ./a */

/*
https://www.libsdl.org/release/SDL-1.2.15/docs/html/guidevideoopengl.html ||
SDL_Delay( 30 ); // added  ||

ported from SDL1 to SDL2
https://wiki.libsdl.org/MigrationGuide
OpenGL: If you were already using OpenGL directly, your migration is pretty simple. Change your SDL_SetVideoMode() call to SDL_CreateWindow() followed by SDL_GL_CreateContext(), and your SDL_GL_SwapBuffers() call to SDL_GL_SwapWindow(window). All the actual calls into the GL are exactly the same.

https://stackoverflow.com/questions/49585857/error-with-sdl-window

compiled with MSYS2/MinGW64 (provides pacman) ||
pacman -Fy sdl2-config ||
pacman -S --needed mingw-w64-x86_64-SDL2 # SDL2 : sdl2-config . not : (SDL1/SDL : sdl-config)
*/

/*
 * SDL OpenGL Tutorial.
 * (c) Michael Vance, 2000
 * briareos@lokigames.com
 *
 * Distributed under terms of the LGPL.
 */

#include <SDL2/SDL.h>
#include <GL/gl.h>
#include <GL/glu.h>

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

static GLboolean should_rotate = GL_TRUE;

SDL_Window* window;


static void quit_tutorial( int code )
{
    /*
     * Quit SDL so we can release the fullscreen
     * mode and restore the previous video settings,
     * etc.
     */
    SDL_Quit( );

    /* Exit program. */
    exit( code );
}

static void handle_key_down( SDL_Keysym* keysym )
{

    /*
     * We're only interested if 'Esc' has
     * been presssed.
     *
     * EXERCISE:
     * Handle the arrow keys and have that change the
     * viewing position/angle.
     */
    switch( keysym->sym ) {
    case SDLK_ESCAPE:
        quit_tutorial( 0 );
        break;
    case SDLK_SPACE:
        should_rotate = !should_rotate;
        break;
    default:
        break;
    }

}

static void process_events( void )
{
    /* Our SDL event placeholder. */
    SDL_Event event;

    /* Grab all the events off the queue. */
    while( SDL_PollEvent( &event ) ) {

        switch( event.type ) {
        case SDL_KEYDOWN:
            /* Handle key presses. */
            handle_key_down( &event.key.keysym );
            break;
        case SDL_QUIT:
            /* Handle quit requests (like Ctrl-c). */
            quit_tutorial( 0 );
            break;
        }

    }

}

static void draw_screen( void )
{
    /* Our angle of rotation. */
    static float angle = 0.0f;

    /*
     * EXERCISE:
     * Replace this awful mess with vertex
     * arrays and a call to glDrawElements.
     *
     * EXERCISE:
     * After completing the above, change
     * it to use compiled vertex arrays.
     *
     * EXERCISE:
     * Verify my windings are correct here ;).
     */
    static GLfloat v0[] = { -1.0f, -1.0f,  1.0f };
    static GLfloat v1[] = {  1.0f, -1.0f,  1.0f };
    static GLfloat v2[] = {  1.0f,  1.0f,  1.0f };
    static GLfloat v3[] = { -1.0f,  1.0f,  1.0f };
    static GLfloat v4[] = { -1.0f, -1.0f, -1.0f };
    static GLfloat v5[] = {  1.0f, -1.0f, -1.0f };
    static GLfloat v6[] = {  1.0f,  1.0f, -1.0f };
    static GLfloat v7[] = { -1.0f,  1.0f, -1.0f };
    static GLubyte red[]    = { 255,   0,   0, 255 };
    static GLubyte green[]  = {   0, 255,   0, 255 };
    static GLubyte blue[]   = {   0,   0, 255, 255 };
    static GLubyte white[]  = { 255, 255, 255, 255 };
    static GLubyte yellow[] = {   0, 255, 255, 255 };
    static GLubyte black[]  = {   0,   0,   0, 255 };
    static GLubyte orange[] = { 255, 255,   0, 255 };
    static GLubyte purple[] = { 255,   0, 255,   0 };

    /* Clear the color and depth buffers. */
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    /* We don't want to modify the projection matrix. */
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity( );

    /* Move down the z-axis. */
    glTranslatef( 0.0, 0.0, -5.0 );

    /* Rotate. */
    glRotatef( angle, 0.0, 1.0, 0.0 );

    if( should_rotate ) {

        if( ++angle > 360.0f ) {
            angle = 0.0f;
        }

    }

    /* Send our triangle data to the pipeline. */
    glBegin( GL_TRIANGLES );

    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( blue );
    glVertex3fv( v2 );

    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( blue );
    glVertex3fv( v2 );
    glColor4ubv( white );
    glVertex3fv( v3 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( black );
    glVertex3fv( v5 );
    glColor4ubv( orange );
    glVertex3fv( v6 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( orange );
    glVertex3fv( v6 );
    glColor4ubv( blue );
    glVertex3fv( v2 );

    glColor4ubv( black );
    glVertex3fv( v5 );
    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( purple );
    glVertex3fv( v7 );

    glColor4ubv( black );
    glVertex3fv( v5 );
    glColor4ubv( purple );
    glVertex3fv( v7 );
    glColor4ubv( orange );
    glVertex3fv( v6 );

    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( white );
    glVertex3fv( v3 );

    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( white );
    glVertex3fv( v3 );
    glColor4ubv( purple );
    glVertex3fv( v7 );

    glColor4ubv( white );
    glVertex3fv( v3 );
    glColor4ubv( blue );
    glVertex3fv( v2 );
    glColor4ubv( orange );
    glVertex3fv( v6 );

    glColor4ubv( white );
    glVertex3fv( v3 );
    glColor4ubv( orange );
    glVertex3fv( v6 );
    glColor4ubv( purple );
    glVertex3fv( v7 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( red );
    glVertex3fv( v0 );
    glColor4ubv( yellow );
    glVertex3fv( v4 );

    glColor4ubv( green );
    glVertex3fv( v1 );
    glColor4ubv( yellow );
    glVertex3fv( v4 );
    glColor4ubv( black );
    glVertex3fv( v5 );

    glEnd( );

    /*
     * EXERCISE:
     * Draw text telling the user that 'Spc'
     * pauses the rotation and 'Esc' quits.
     * Do it using vetors and textured quads.
     */

    /*
     * Swap the buffers. This this tells the driver to
     * render the next frame from the contents of the
     * back-buffer, and to set all rendering operations
     * to occur on what was the front-buffer.
     *
     * Double buffering prevents nasty visual tearing
     * from the application drawing on areas of the
     * screen that are being updated at the same time.
     */
    //SDL_GL_SwapBuffers( ); // SDL1
    // SDL2:
    SDL_GL_SwapWindow(window);

    /*
    ported from SDL1 to SDL2
https://wiki.libsdl.org/MigrationGuide
OpenGL: If you were already using OpenGL directly, your migration is pretty simple. Change your SDL_SetVideoMode() call to SDL_CreateWindow() followed by SDL_GL_CreateContext(), and your SDL_GL_SwapBuffers() call to SDL_GL_SwapWindow(window). All the actual calls into the GL are exactly the same.
    */
}

static void setup_opengl( int width, int height )
{
    float ratio = (float) width / (float) height;

    /* Our shading model--Gouraud (smooth). */
    glShadeModel( GL_SMOOTH );

    /* Culling. */
    glCullFace( GL_BACK );
    glFrontFace( GL_CCW );
    glEnable( GL_CULL_FACE );

    /* Set the clear color. */
    glClearColor( 0, 0, 0, 0 );

    /* Setup our viewport. */
    glViewport( 0, 0, width, height );

    /*
     * Change to the projection matrix and set
     * our viewing volume.
     */
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity( );
    /*
     * EXERCISE:
     * Replace this with a call to glFrustum.
     */
    gluPerspective( 60.0, ratio, 1.0, 1024.0 );
}

int main( int argc, char* argv[] )
{
    /* Information about the current video settings. */
    ///const SDL_VideoInfo* info = NULL; // SDL1
    /* Dimensions of our window. */
    int width = 0;
    int height = 0;
    /* Color depth in bits of our window. */
    ///int bpp = 0; // SDL1
    /* Flags we will pass into SDL_SetVideoMode. */
    ///int flags = 0; // SDL1

    /* First, initialize SDL's video subsystem. */
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
        /* Failed, exit. */
        fprintf( stderr, "Video initialization failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }

    /* Let's get some video information. */
    //info = SDL_GetVideoInfo( );
    /*
    if( !info ) {
        // This should probably never happen.
        fprintf( stderr, "Video query failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }*/

    /*
     * Set our width/height to 640/480 (you would
     * of course let the user decide this in a normal
     * app). We get the bpp we will request from
     * the display. On X11, VidMode can't change
     * resolution, so this is probably being overly
     * safe. Under Win32, ChangeDisplaySettings
     * can change the bpp.
     */
    width = 640;
    height = 480;
    ///bpp = info->vfmt->BitsPerPixel; // SDL1

    /*
     * Now, we want to setup our requested
     * window attributes for our OpenGL window.
     * We want *at least* 5 bits of red, green
     * and blue. We also want at least a 16-bit
     * depth buffer.
     *
     * The last thing we do is request a double
     * buffered window. '1' turns on double
     * buffering, '0' turns it off.
     *
     * Note that we do not use SDL_DOUBLEBUF in
     * the flags to SDL_SetVideoMode. That does
     * not affect the GL attribute state, only
     * the standard 2D blitting setup.
     */
    SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
    SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );


    /*
    ported from SDL1 to SDL2
https://wiki.libsdl.org/MigrationGuide
OpenGL: If you were already using OpenGL directly, your migration is pretty simple. Change your SDL_SetVideoMode() call to SDL_CreateWindow() followed by SDL_GL_CreateContext(), and your SDL_GL_SwapBuffers() call to SDL_GL_SwapWindow(window). All the actual calls into the GL are exactly the same.
    */
window = SDL_CreateWindow("Game Engine", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, SDL_WINDOW_OPENGL);
SDL_GL_CreateContext(window);

    /*
     * We want to request that SDL provide us
     * with an OpenGL window, in a fullscreen
     * video mode.
     *
     * EXERCISE:
     * Make starting windowed an option, and
     * handle the resize events properly with
     * glViewport.
     */
    //flags = SDL_OPENGL | SDL_FULLSCREEN; // SDL1

    /*
     * Set the video mode
     *
    if( SDL_SetVideoMode( width, height, bpp, flags ) == 0 ) {
         *
         * This could happen for a variety of reasons,
         * including DISPLAY not being set, the specified
         * resolution not being available, etc.
         *
        fprintf( stderr, "Video mode set failed: %s\n",
             SDL_GetError( ) );
        quit_tutorial( 1 );
    }*/

    /*
     * At this point, we should have a properly setup
     * double-buffered window for use with OpenGL.
     */
    setup_opengl( width, height );

    /*
     * Now we want to begin our normal app process--
     * an event loop with a lot of redrawing.
     */
    while( 1 ) {
        /* Process incoming events. */
        process_events( );
        /* Draw the screen. */
        draw_screen( );


        ///////--------------------- MY ADD
        SDL_Delay( 30 );
    }

    /*
     * EXERCISE:
     * Record timings using SDL_GetTicks() and
     * and print out frames per second at program
     * end.
     */

    /* Never reached. */
    return 0;
}