what is the framework using in Blender GUI ?

Question

What is the framework using in Blender GUI? QT? Or Tk, GTK+, FOX toolkit, wxWidgets? Because Blender is cross-platform application.

Answer 1

None of those, apparently. I come to this conclusion from the fact that the Debian-packaged Blender doesn't depend on any GUI toolkit, and based on the threads at the Blender forum here and here. Note the phrase in the second thread:

There is probably zero (or at least quite little) chance of QT or GTK or any other rather heavy gui toolkit being used with Blender.

Answer 2

Blender uses OpenGL to draw all of its user interface. (Personally I'm a fan!)