SDL2/GL context defaults to v3.0 on linux mint - linux

Question

When I compile & run my code to create an opengl 3.3 or above context (identical to the windows version, with one or two extra lines), it defaults to 3.0, which will cause problems with some of my applications I want to port over.
I'm looking for a fix/explanation of this.
Source as follows:
//Using SDL and standard IO
#include <SDL2/SDL.h>
#include <stdio.h>
#include <GL/glew.h>
//Screen dimension constants
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
bool handleEvent(SDL_Event& event)
{
return true;
}
int main( int argc, char* args[] )
{
//The window we'll be rendering to
SDL_Window* window = NULL;
//Initialize SDL
if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
{
printf( "SDL could not initialize! SDL_Error: %s\n", SDL_GetError() );
}
else
{
//Create window
window = SDL_CreateWindow("SDL/GLM/OpenGL Demo", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN );
if( window == NULL )
{
printf( "Window could not be created! SDL_Error: %s\n", SDL_GetError() );
}
else
{
SDL_GLContext context = SDL_GL_CreateContext(window);
SDL_GL_MakeCurrent(window, context);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetSwapInterval(1); // set swap buffers to sync with monitor's vertical refresh rate
glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);
glewExperimental = GL_TRUE;
glClearColor(1.0,0.0,0.0,1.0);
GLenum err = glewInit();
if (err != GLEW_OK)
{
printf("glew init failed: %s!\n", glewGetErrorString(err));
}
printf("opengl version :%s\n",glGetString(GL_VERSION));
bool running = true; // set running to true
SDL_Event sdlEvent; // variable to detect SDL events
while (running)
{ // the event loop
while (SDL_PollEvent(&sdlEvent))
{
if (sdlEvent.type == SDL_QUIT)
running = false;
else
{
running = handleEvent(sdlEvent);
}
}
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
SDL_GL_SwapWindow(window);
}
SDL_GL_DeleteContext(context);
SDL_DestroyWindow(window);
}
}
SDL_Quit();
return 0;
}

Answer 1

You need to set GL attributes before you create a window, not after you create a context:
SDL_GL_SetAttribute()
Use this function to set an OpenGL window attribute before window creation.
Example:
#include <GL/glew.h>
#include <SDL2/SDL.h>
#include <iostream>
int main( int argc, char** argv )
{
SDL_Init( SDL_INIT_EVERYTHING );
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_Window* window = SDL_CreateWindow
(
"SDL2",
SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
300, 300,
SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL
);
if( NULL == window )
{
std::cerr << "Failed to create window: " << SDL_GetError() << std::endl;
SDL_Quit();
return 0;
}
SDL_GLContext context = SDL_GL_CreateContext(window);
if( NULL == context )
{
std::cerr << "Failed to create GL context: " << SDL_GetError() << std::endl;
SDL_DestroyWindow( window );
SDL_Quit();
return -1;
}
if( SDL_GL_MakeCurrent( window, context ) < 0 )
{
std::cerr << "Failed to make GL context current: " << SDL_GetError() << std::endl;
SDL_GL_DeleteContext( context );
SDL_DestroyWindow( window );
SDL_Quit();
return -1;
}
std::cout << "GL_VERSION: " << glGetString( GL_VERSION ) << std::endl;
SDL_GL_SetSwapInterval(1);
glewExperimental = GL_TRUE;
GLenum err = glewInit();
if( GLEW_OK != err )
{
std::cerr << "Failed init GLEW: " << glewGetErrorString( err ) << std::endl;
SDL_GL_DeleteContext( context );
SDL_DestroyWindow( window );
SDL_Quit();
return -1;
}
bool running = true;
while( running )
{
SDL_Event ev;
while( SDL_PollEvent( &ev ) )
{
if ( ev.type == SDL_QUIT )
running = false;
}
glClear( GL_COLOR_BUFFER_BIT );
SDL_GL_SwapWindow( window );
}
SDL_GL_DeleteContext( context );
SDL_DestroyWindow( window );
SDL_Quit();
return 0;
}

Answer 2

As it turns out, mesa drivers do not support OpenGL contexts above 3.0, so the driver will default to the maximum available, which is 3.0. In order to create a 3.x context, you must have proprietary drivers installed. Once I had installed those drivers everything worked fine.