Some help for openGL

I know that if I wan to use print something in openGL, I would used this

Code:

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glutDisplayFunc(renderScene);

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But now the problem is in my code, if I wan to display something in the screen, I use this.

Code:

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if (myKeys['o'] == true)
{
    glutDisplayFunc(renderScene);
}

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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:

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if (myKeys['o'] == true)
{
    myApplication::renderScene();
}

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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.

Quote:

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Originally Posted by evildotaing

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

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this error message is very clear. You have to use

Code:

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if (myKeys['o'] == true)
{
    glutDisplayFunc( &myApplication::renderScene );
}

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myApplication::renderScene() has to be a static memberfunction of myApplication.
Kurt

Quote:

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Originally Posted by ZuK

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

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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:

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static myApplication* getInstance();

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And all my codes work expect when I dun know why got problem when I want to use glutDisplayFunc.

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

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

How to do it. Help? Example of some code, I am very confused.

Quote:

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Originally Posted by Elkvis

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

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I make the function to static void(renderScene); but still not working.

Quote:

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Originally Posted by evildotaing

I make the function to static void(renderScene); but still not working.

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it should be

Code:

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static void renderScene();

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If it still won't work then post your code and full error messages.
Kurt

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

Code:

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// 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 );
}

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Kurt

Glut is expecting a function pointer to a global C-style function. You can try to use a static member function, but beware:

Quote:

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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.

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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:

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// 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

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Sometimes you don't have to be that extreme but that's something you can try.