Missing GL version

[shogun1234]

I am completely new to glew, opengl, etc. Recently I encounter a problem where an error message shows 'Missing GL version'

The code where error is thrown

        ...
        Window* window = new Window();
 
        GLenum err = glewInit();
        if (err != GLEW_OK)
        {
                std::cout << "Glew Error: " << glewGetErrorString(err) << std::endl;
                return -1;
        }
        ...
 

After searching on the internet, it looks like glcontext is not created appropriately.


But within window variable, it has

        SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
        SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 32);
 
        _window = SDL_CreateWindow("My Game Window",
                0,
                0,
                1024, 768,
                SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
 
        _glcontext = SDL_GL_CreateContext(_window);
 

Others (http://stackoverflow.com/questions/13826150/sdl2-opengl3-how-to-initialize-sdl-inside-a-function) mentions the reference problem. I then tried copying the above code snippet to replace the line

        Window* window = new Window();
 

So the code looks like

int main(int argc, char *argv[])
{
        SDL_Window* _window;
        SDL_GLContext _glcontext
 
        SDL_Init(SDL_INIT_EVERYTHING);;
 
        SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
        SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 32);
 
        _window = SDL_CreateWindow("My Game Window",
                0,
                0,
                1024, 768,
                SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
 
        _glcontext = SDL_GL_CreateContext(_window);
 
        GLenum err = glewInit();
        if (err != GLEW_OK)
        {
                std::cout << "Glew Error: -> " << glewGetErrorString(err) << std::endl;
                return -1;
        }
        ...
}
 

However, it still throws 'Missing GL version'

Any place I may miss? What might cause such error and how to fix it?

I appreciate any suggestion.

[SneakySnake]

It seems that calling SDL_GL_* functions before context creation can mess things up (which makes sense if you think about it). I get the same error as you if I run your code.

However, if I move the SDL_GL_* calls after the context creation, I don't get any errors from glewInit().

#include <SDL2/SDL.h>
#include <GL/glew.h>

#include <iostream>

int main(int argc, char *argv[])
{
        SDL_Window* _window;
        SDL_GLContext _glcontext;
 
        SDL_Init(SDL_INIT_EVERYTHING);;
 
        _window = SDL_CreateWindow("My Game Window",
                0,
                0,
                1024, 768,
                SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
 
        _glcontext = SDL_GL_CreateContext(_window);
        
        // Now that the context is created, we can call our SDL_GL_ functions
        SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
        SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 32);
 
        GLenum err = glewInit();
        
        if (err != GLEW_OK)
        {
                std::cout << "Glew Error: -> " << glewGetErrorString(err) << std::endl;
                return -1;
        }
        
        SDL_Quit();
}

It might be an even better idea to fiddle with the context after glewInit(), so glewInit() has a clean context to work with, but I don't know anything about how glewInit() works.

[shogun1234]

Thanks for the advice. It helps me find out the cause. I google again and notice that, although the flow is correct with following order

SDL_GL_SetAttribute()
...
SDL_CreateWindow()
...
SDL_GL_CreateContext()

stated at http://wiki.libsdl.org/SDL_GL_SetAttribute

The SDL_GL_DEPTH_SIZE in the example described is 16, instead of the 32 in the source that doesn't work.

SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 32);

Changing SDL_GL_DEPTH_SIZE value from 32 to 16 or 24 gets rid of 'Missing GL version' error message.

Thanks again for your help! That's very useful.

[S6k9GNh0]

shogun1234, that's odd... that's not included in any of my examples. The DEPTH_SIZE also shouldn't affect OpenGL initialization from GLEW... Just remove that line and a sane default will be chosen, especially if you don't know what that is or don't use it.

Anyways, I would suggest setting the variable "glewExperimental" to "true". You also need to set the OpenGL version wanted.

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);

Or else you'll get a rather old compatibility version, regardless of platform or headers used. You should set attributes before creating a context or window!

Remember that SDL is a C library. In this case, none of its structures have constructors so using something like "new" on them is really, really bad and asking for a memory leak somewhere. You must use their facilities to initialize and close out a structure!