Thread: [GLUT] Pointers to class methods

I've created a little class which basically wraps up a little demo type thing I've written while following various GLUT tutorials and I need to make the calls to the "glutXFunc" (eg. glutDisplayFunc) but I'm stumped on how to give it a class method as a parameter.

Here's the function - initGLUT () - which attempts to do this:

Code:

void initGLUT ()
{
        glutInitDisplayMode (GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
        glClearColor (0.0f, 0.0f, 0.0f, 0.0f);

        glutInitWindowPosition (0, 0);
        glutInitWindowSize (640, 480);
        glutCreateWindow ("Engine Demo");
        glEnable (GL_DEPTH_TEST);

        glutDisplayFunc (engineDemo::render);  // problem line

        // haven't tackled these yet so ignore them
        glutReshapeFunc (reshape);
        glutIdleFunc (render);
        glutKeyboardFunc (normalKeys);
        glutSpecialFunc (specialKeys);
        glutMouseFunc (mousePress);
        glutPassiveMotionFunc (mousePassiveMotion);
}

The syntax is pretty tortured:

Code:

#include <iostream>
#include <string>
using namespace std;

class Dog
{
public:
	string bark(int num)
	{
		for(int i = 0; i<num; i++)
			cout<<"Woof!";

		cout<<endl;
		
		return "I finished barking.";
	}
};

void someFunc(const Dog& aDog, string(Dog::*pDogFunc)(int) )
{
	string result = (aDog.*pDogFunc)(3);
	cout<<result<<endl;
}

int main()
{
	Dog myDog;
	string(Dog::*pFunc)(int) = Dog::bark;
	someFunc(myDog, pFunc);

	return 0;
}

Ok I've given it my best shot:

Code:

void initGLUT ()
{
        void (engineDemo::*p_Render) (void) = engineDemo::render;

        glutInitDisplayMode (GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
        glClearColor (0.0f, 0.0f, 0.0f, 0.0f);

        glutInitWindowPosition (0, 0);
        glutInitWindowSize (640, 480);
        glutCreateWindow ("Engine Demo");
        glEnable (GL_DEPTH_TEST);

        glutDisplayFunc (p_Render);
        glutReshapeFunc (reshape);
        glutIdleFunc (render);
        glutKeyboardFunc (normalKeys);
        glutSpecialFunc (specialKeys);
        glutMouseFunc (mousePress);
        glutPassiveMotionFunc (mousePassiveMotion);
}

EDIT: Oh yeah, the errors:

Code:

c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(283) : error C2664: 'glutDisplayFunc' : cannot convert parameter 1 from 'void (__thiscall engineDemo::* )(void)' to 'void (__cdecl *)(void)'
        There is no context in which this conversion is possible

If you make the function inside the render class static you should be able to send it to glutDisplayFunc.

Ok I'll try that quick.

It sort of worked. There were probs except I've had to make everything in the class static and the linker threw up unresolved externals because I forgot to type static in front of all the definitions, but when I did that I now get these:

Code:

------ Build started: Project: glutProj, Configuration: Debug Win32 ------

Compiling...
glutProj.cpp
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(98) : error C2724: 'engineDemo::renderString' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(107) : error C2724: 'engineDemo::playSound' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(118) : error C2724: 'engineDemo::setOrthoProjection' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(143) : error C2724: 'engineDemo::resetPerspectiveProjection' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(151) : error C2724: 'engineDemo::render' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(188) : error C2724: 'engineDemo::reshape' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(208) : error C2724: 'engineDemo::normalKeys' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(221) : error C2724: 'engineDemo::specialKeys' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(243) : error C2724: 'engineDemo::mousePress' : 'static' should not be used on member functions defined at file scope
c:\Documents and Settings\lee\Desktop\glutProj\glutProj.cpp(265) : error C2724: 'engineDemo::mousePassiveMotion' : 'static' should not be used on member functions defined at file scope

Build Time 0:00
Build log was saved at "file://c:\Documents and Settings\lee\Desktop\glutProj\Debug\BuildLog.htm"
glutProj - 10 error(s), 0 warning(s)


---------------------- Done ----------------------

    Build: 0 succeeded, 1 failed, 0 skipped

I've never had these before.
Oh yeah I don't understand how making them static 'makes it work'?

Yes I do have it in a .h & .cpp but I'd be surprised to learn that this is the problem

Don't you want:

Code:

void Demo::playSound ()
{
        m_Result = m_FMOD_System->playSound (FMOD_CHANNEL_FREE, m_Sound, false, 0);
        if (m_Result != FMOD_OK) {
                MessageBox (0, "Error playing sound", "FMOD Error",
                                MB_OK | MB_ICONEXCLAMATION);
                exit (1);
        }
}