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++)

score 4 · Accepted Answer · edited May 23 '17 at 10:27

4

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

edited May 23 '17 at 10:27

Community

1
1

answered Apr 19 '10 at 20:24

Fred Larson

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18
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174

score 2 · Answer 2 · answered Apr 19 '10 at 20:26

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();}
}

score 0 · Answer 3 · answered Jun 12 '14 at 08:10

0

I've just searched around for this, since I had the same problem when cleaning up and OOP'ing our code. Turns out that the nice stuff like std::bind doesn't work here, but if you're compiling on C++11 anyway you can actually define an anonymous function to wrap your member function.

class Renderer {
  void Start();
  void Render();
}

// ...

void Renderer::Start() {
  // ...
  glutDisplayFunc([](){ Render(); });
}

answered Jun 12 '14 at 08:10

Michael Nett

375
1
10

This code snippet produces an `error: ‘this’ was not captured for this lambda function`, how do I fix this? – William Nov 12 '14 at 23:43
`error: invalid use of non-static member function glutDisplayFunc([](){ draw; });` – e-info128 Jan 14 '18 at 05:36

score 0 · Answer 4 · answered Apr 19 '10 at 20:25

A simple workaround is :

Declare a global pointer to your class and initialize it in main(), let the callback call a regular method on that instance

MyOGLClass *g_pOGL;

void oglDraw()
{
    if(g_pOGL)
        g_pOGL->oglDraw();
}

void main()
{
    // Init your class
    MyOGLClass o;

    g_pOGL = &o;

    //...

    glutMainLoop();

}

The limitation is you can have only one instance of your class, but for an OpenGL app that isn't so bad as you really need only one anyway...

How to pass non static member function into glutDisplayFunc

4 Answers4