Tutorial1: Creating a Cross Platform OpenGL 3.2 Context in SDL (C / SDL)

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Revision as of 08:10, 21 August 2009 by JasonBorden (talk | contribs) (formatting change)
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Overview

This tutorial is designed to help explain the process of creating an OpenGL 3.2 context using libsdl.

This tutorial has the following requirements:

  • An OpenGL 3.2 compatible video card. (Currently an NVDIA G80 or ATI R600 or newer GPU)
  • An OpenGL 3.2 video driver. (Currently they are all beta versions)
  • libsdl-1.3 which is currently in development phase, but includes support for OpenGL 3 style contexts.
  • gl3.h installed in a 'GL3' directory. (e.g. mkdir /usr/include/GL3 ; mv gl3.h /usr/include/GL3)

The benefits of using libsdl are numerous, but in particular, it will allow our code to run on windows, mac, and unix / linux. My only computer which meets the above requirements runs linux, so I can guarantee compatibility with linux only. If you find problems compiling the code on other platforms, please make a note of it.

Creating a window in libsdl and binding an OpenGL 3.2 context to it uses these steps:

  • Initialize the SDL video subsystem using SDL_Init or SDL_VideoInit. (We use SDL_Init in this example)
  • Set the parameters we require for opengl using SDL_GL_SetAttribute.
  • Create a window using SDL_CreateWindow.
  • Bind an OpenGL context to the window using SDL_GL_CreateContext.

The Code

#include <stdio.h>
#include <stdlib.h>
/* Ensure we are using opengl's core profile only */
#define GL3_PROTOTYPES 1
#include <GL3/gl3.h>

#include <SDL.h>
#define PROGRAM_NAME "Tutorial1"

/* A simple function that prints a message, the error code returned by SDL,
 * and quits the application */
void sdldie(char *msg)
{
    printf("%s: %s\n", msg, SDL_GetError());
    SDL_Quit();
    exit(1);
}

/* Our program's entry point */
int main(int argc, char *argv[])
{
    SDL_WindowID mainwindow; /* Our window handle */
    SDL_GLContext maincontext; /* Our opengl context handle */

    if (SDL_Init(SDL_INIT_VIDEO) < 0) /* Initialize SDL's Video subsystem */
        sdldie("Unable to initialize SDL"); /* Or die on error */

    /* Request an opengl 3.2 context.
     * SDL doesn't have the ability to choose which profile at this time of writing,
     * but it should default to the core profile */
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);

    /* Turn on double buffering with a 24bit Z buffer.
     * You may need to change this to 16 or 32 for your system */
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

    /* Create our window centered at 512x512 resolution */
    mainwindow = SDL_CreateWindow(PROGRAM_NAME, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        512, 512, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
    if (!mainwindow) /* Die if creation failed */
        sdldie("Unable to create window");

    /* Create our opengl context and attach it to our window */
    maincontext = SDL_GL_CreateContext(mainwindow);

    /* This makes our buffer swap syncronized with the monitor's vertical refresh */
    SDL_GL_SetSwapInterval(1);

    /* Clear our buffer with a red background */
    glClearColor ( 1.0, 0.0, 0.0, 1.0 );
    glClear ( GL_COLOR_BUFFER_BIT );
    /* Swap our back buffer to the front */
    SDL_GL_SwapWindow(mainwindow);
    /* Wait 2 seconds */
    SDL_Delay(2000);

    /* Same as above, but green */
    glClearColor ( 0.0, 1.0, 0.0, 1.0 );
    glClear ( GL_COLOR_BUFFER_BIT );
    SDL_GL_SwapWindow(mainwindow);
    SDL_Delay(2000);

    /* Same as above, but blue */
    glClearColor ( 0.0, 0.0, 1.0, 1.0 );
    glClear ( GL_COLOR_BUFFER_BIT );
    SDL_GL_SwapWindow(mainwindow);
    SDL_Delay(2000);

    /* Delete our opengl context, destroy our window, and shutdown SDL */
    SDL_GL_DeleteContext(maincontext);
    SDL_DestroyWindow(mainwindow);
    SDL_Quit();

    return 0;
}

Compilation

On linux: gcc tutorial1.c -o tutorial1 -lGL $(sdl-config --cflags --libs)

If you have libsdl-1.2 and libsdl-1.3 both installed, make sure to run the appropriate version of sdl-config. For example if you installed sdl-1.3 to /usr/local:

gcc -o tutorial1 -lGL $(/usr/local/bin/sdl-config --cflags --libs)

Execution

./tutorial1 The result should be a 512x512 window centered on your display showing a red, green, then blue background.