What is the GTK equivalent of
SetWindowLongPtr((HWND)handle,GWLP_WNDPROC,(LONG_PTR)eventCallback);
I want to draw custom stuff in a slider/trackbar/fader control.
There is the "draw" signal, RTM g_signal_connect (widget, "draw", G_CALLBACK (your_callback), fancy_extra_state_data_you_may_need_or_not);