How to pass non static member function into glutDisplayFunc

Question

I have a class which has functionality to initialise opengl and run it in separate thread.

My problem is: openGL callbacks such as glutDisplayFunc, glutMotionFunc etc accepts void (*f) void, and I cannot pass class member function.

ways around. 1) I can declare member function as static, but in this case I need to declare all used member variables as static, and end up declaring a whole class as a static.

2) I can use some stand alone function and declare my object as global, but its too bad.

I wonder if there are some ways around so I dont need to make my opengl class static ?? (using c++)

Answer 1

You'll need to create a "thunk" or "trampoline": C API function callbacks into C++ member function code

Answer 2

Since the callbacks don't take any parameters, there is not much you can do. One possibility is to create a namespace with functions and a static data member which is your current class. The functions would just forward the function calls to the existing class. This is just basically a slightly cleaner version of your #2.

namespace GLForwader
{
    static MyGLClass* = new myGlClass();

    void glutDisplayFunc() {myGlClass->glutDisplayFunc();}
    void glutMotionFunc() {myGlClass->glutMotionFunc();}
}