[Interest] Divining the opengl versions available

[Boudewijn Rempt]

Hi,

I need to know whether my users have opengl 2.1, 3.2 with compatibility profile
or 3.2 with core profile only, and I'm having a hard time getting that information
through Qt 5's opengl support. With Qt4, I used something like this:

     if (QGLFormat::openGLVersionFlags() & QGLFormat::OpenGL_Version_2_1)
         qDebug() << "OpenGL version 2.1 or higher is present.";
     if (QGLFormat::openGLVersionFlags() & QGLFormat::OpenGL_Version_3_2)
         qDebug() << "OpenGL version 3.1 or higher is present.";

But that module is deprecated, so I'm trying not to use it. But I cannot figure out
another way of checking the version by trying to create a vernsionfunctions object
and see if it's 0 or not:

         QOpenGLContext *context = 0;
         QSurfaceFormat format;

         // 3.2 Compatibility
         format.setMajorVersion( 3 );
         format.setMinorVersion( 2 );
         format.setProfile( QSurfaceFormat::CoreProfile );
         setFormat( format );
         // Create an OpenGL context
         context = new QOpenGLContext;
         context->setFormat( format );
         context->create();
         context->makeCurrent(this);
         QOpenGLFunctions_3_2_Core *f0 = context->versionFunctions<QOpenGLFunctions_3_2_Core>();
         version32Core = f0;
         delete context;

         // 3.2 Core
         format.setProfile( QSurfaceFormat::CompatibilityProfile );
         setFormat( format );
         // Create an OpenGL context
         context = new QOpenGLContext;
         context->setFormat( format );
         context->create();
         context->makeCurrent(this);
         QOpenGLFunctions_3_2_Compatibility *f1 = context->versionFunctions<QOpenGLFunctions_3_2_Compatibility>();
         version32Compatibility = f1;
         delete context;

         // 2.1
         format.setMajorVersion( 3 );
         format.setMinorVersion( 2 );
         setFormat( format );
         // Create an OpenGL context
         context = new QOpenGLContext;
         context->setFormat( format );
         context->create();
         context->makeCurrent(this);
         QOpenGLFunctions_2_1 *f2 = context->versionFunctions<QOpenGLFunctions_2_1>();
         version32Core = f2;
         delete context;

But that sometimes fails as well, on some Linux systems where I know that the system supports
3.2 + compatibility profile, I don't get the functions object either. What's the correct way
to see which version is supported?

Boudewijn