Hmm, the trick is that class is not part of any of the OpenGL libraries in VTK. It is a API generic class. So I’m not sure how it will get the value of the definition. It must be working for you somehow but I’m not seeing where it could get that definition. Normally it is provided by gl.h but that is not included here.
So what I am thinking is that the way to do this is to add an ivar like UsePointData, that defaults to false but can be turned on. For your code you would set it to true and then it would use your new code paths. Does that work for you?