The requested and the actual format may differ. Requesting a given OpenGL version does not mean the resulting context will target exactly the requested version. It is only guaranteed that the version/profile/options combination for the created context is compatible with the request, as long as the driver is able to provide such a context.

For example, requesting an OpenGL version 3.x core profile context may result in an OpenGL 4.x core profile context. Similarly, a request for OpenGL 2.1 may result in an OpenGL 3.0 context with deprecated functions enabled. Finally, depending on the driver, unsupported versions may result in either a context creation failure or in a context for the highest supported version.

It is possible to request a functions object for a different version and profile than that for which the context was created. To do this either use the template version of this function specifying the desired functions object type as the template parameter or by passing in a QOpenGLVersionProfile object as an argument to the non-template function.

Note that requests for function objects of other versions or profiles can fail and in doing so will return a null pointer. Situations in which creation of the functions object can fail are if the request cannot be satisfied due to asking for functions that are not in the version or profile of this context. For example:

Code: [Select]

QOpenGLFunctions_3_3_Core* funcs = 0;
  funcs = context->versionFunctions<QOpenGLFunctions_3_3_Core>();
  if (!funcs) {
      qWarning() << "Could not obtain required OpenGL context version";
      exit(1);
  }Requesting a 3.3 core profile functions object would succeed.
Requesting a 3.3 compatibility profile functions object would fail. We would fail to resolve the deprecated functions.
Requesting a 4.3 core profile functions object would fail. We would fail to resolve the new core functions introduced in versions 4.0-4.3.
Requesting a 3.1 functions object would succeed. There is nothing in 3.1 that is not also in 3.3 core.