Some help for openGL

This is a discussion on Some help for openGL within the C++ Programming forums, part of the General Programming Boards category; I know that if I wan to use print something in openGL, I would used this Code: glutDisplayFunc(renderScene); But now ...

  1. #1
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    Some help for openGL

    I know that if I wan to use print something in openGL, I would used this
    Code:
    glutDisplayFunc(renderScene);
    But now the problem is in my code, if I wan to display something in the screen, I use this.
    Code:
    if (myKeys['o'] == true)
    {
        glutDisplayFunc(renderScene);
    }
    It would not work because I am using pointer. I received this error.

    error C3867: 'myApplication::renderScene': function call missing argument list; use '&myApplication::renderScene' to create a pointer to member


    So I edit and change to this.
    Code:
    if (myKeys['o'] == true)
    {
        myApplication::renderScene();
    }
    It work but the problem is I need to include the glutDisplayFunc too. How should I do this to code that include the glutDisplayFunc in my application class with the function render scene.

  2. #2
    ZuK
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    Quote Originally Posted by evildotaing View Post
    error C3867: 'myApplication::renderScene': function call missing argument list; use '&myApplication::renderScene' to create a pointer to member
    this error message is very clear. You have to use

    Code:
    if (myKeys['o'] == true)
    {
         glutDisplayFunc( &myApplication::renderScene );
    }
    myApplication::renderScene() has to be a static memberfunction of myApplication.
    Kurt

  3. #3
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    Quote Originally Posted by ZuK View Post
    this error message is very clear. You have to use

    Code:
    if (myKeys['o'] == true)
    {
         glutDisplayFunc( &myApplication::renderScene );
    }
    myApplication::renderScene() has to be a static memberfunction of myApplication.
    Kurt
    I code what you are saying but now I got new error again. error C2664: 'glutDisplayFunc' : cannot convert parameter 1 from 'void (__thiscall myApplication::* )(void)' to 'void (__cdecl *)(void)' Anyway I declared as this for pointer,
    Code:
    static myApplication* getInstance();
    And all my codes work expect when I dun know why got problem when I want to use glutDisplayFunc.

  4. #4
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    You simply get a calling convention conflict: the glut library is probably in C and expect a function using C calling convention, but you pass a class method that takes an implicit this pointer.
    This is what your compilers tries to tell you.
    You have to make the renderScene method a static method of the class as Kurt said it before.
    Also check that stackoverflow thread which concerns the same issue: c++ - Using OpenGL glutDisplayFunc within class - Stack Overflow

  5. #5
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    __thiscall usually only applies to non-static member functions. you need to make myApplication::renderScene static.

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    How to do it. Help? Example of some code, I am very confused.
    Last edited by evildotaing; 08-20-2012 at 04:12 AM.

  7. #7
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    Quote Originally Posted by Elkvis View Post
    __thiscall usually only applies to non-static member functions. you need to make myApplication::renderScene static.
    I make the function to static void(renderScene); but still not working.

  8. #8
    ZuK
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    Quote Originally Posted by evildotaing View Post
    I make the function to static void(renderScene); but still not working.
    it should be
    Code:
    static void renderScene();
    If it still won't work then post your code and full error messages.
    Kurt

  9. #9
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    I got this error doing making renderScene static. 1>h:\game protype project\game_v4\dm2231_lab_v4\dm2231_lab\myapplica tion.cpp(238) : error C2724: 'myApplication::renderScene' : 'static' should not be used on member functions defined at file scope

  10. #10
    ZuK
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    Code:
    // in header
    class myApplication {
        public:
        static void renderScene();
        // .....
    };
    
    // in myapp.cpp
    
    void myApplication::renderScene() {  // no static needed here
        // do whatever
    }
    
    // in main.cpp
    
    int main() {
        // update display
        glutDisplayFunc( &myApplication::renderScene );
    }
    Kurt

  11. #11
    Frequently Quite Prolix dwks's Avatar
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    Glut is expecting a function pointer to a global C-style function. You can try to use a static member function, but beware:
    static member functions can be used in the contexts where a C callback is expected, if they are extern "C". Although on most compilers it would probably work without extern "C", the standard says it doesn't have to work.
    From C++ FQA Lite: Pointers to member functions

    Of course it would be a pain to use extern "C" member functions... Here's what I normally do if I can't get this kind of thing to work. Declare a global function, and just to be safe make it extern "C", and then call whatever function you really want to handle things.
    Code:
    // in .h
    class SomeClass {
    public:
        static void handleDisplay();
    };
    
    // in .cpp
    // note: in the .cpp file, you should leave out keywords like "static" and "virtual"; that was the cause of your second error message
    void SomeClass::handleDisplay() {
        // ...
    }
    
    // You can prototype this function if you really want to, but it's not really necessary
    extern "C" {
        void handler() {  // if you put "static" here, the function is only visible from within this file
            // can use C++ code here even though it's extern "C"
            SomeClass::handleDisplay();
        }
    }
    
    // okay, now we have a real C-style function we can pass to glut
    glutDisplayFunc(handler);  // & is optional on handler
    Sometimes you don't have to be that extreme but that's something you can try.
    dwk

    Seek and ye shall find. quaere et invenies.

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