مساعدة بسيطة في رسم دائرة

السلام عليكــم ورحمـة الله وبركاتــه ،،

حاولت ارسم دائرة عن طريق التناظر

لكن صار فيه مشكلة في استدعاء دالة و انا نسيت شوي c++

فأتمنى تصححون كودي

رسالة الخطأ:

error C2664: 'glutDisplayFunc' : cannot convert parameter 1 from 'void' to 'void (__cdecl *)(void)'

#include <glut.h>


class screenPt
{
private:
	GLint x,y;
public:
	screenPt()
	{
		x=y=0;
	}
	void setCoords(GLint xCoordValue,GLint yCoordValue)
	{
		x=xCoordValue;
		y=yCoordValue;
	}
	GLint getx()const
	{
		return x;
	}
	GLint gety()const
	{
		return y;
	}


void incrementx()
{
	x++;
}
void decrementy()
{
	y--;
}

void setPixel(GLint xCoord,GLint yCoord)
{
	glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_POINTS);
	   glVertex2i(xCoord,yCoord);
	   glEnd();

}


	void Init()
{
	glClearColor(1,1,1,1);
	glColor3f(1,0,0);
	glPointSize(2);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	gluOrtho2D(-200,200,-250,250);
}
	void circleMidpoint(GLint xc,GLint yc,GLint radius)
{
	screenPt circPt;
	GLint p=1-radius;
	circPt.setCoords(0,radius);
	//circlePlotPoints(GLint ,GLint,screenPt);
	circlePlotPoints(xc,yc,circPt);
	while (circPt.getx() < circPt.gety())
	{
		circPt.incrementx();
		if (p<0)
			p+=2*circPt.getx() +1;
		else{
			circPt.decrementy();
			p+=2*circPt.getx() - circPt.gety()+1;
		}
		circlePlotPoints(xc,yc,circPt);
	}
}
void circlePlotPoints(GLint xc,GLint yc, screenPt circPt)
{
	setPixel (xc + circPt.getx() , yc + circPt.gety());
	setPixel (xc - circPt.getx() , yc + circPt.gety());
	setPixel (xc + circPt.getx() , yc - circPt.gety());
	setPixel (xc - circPt.getx() , yc - circPt.gety());
	setPixel (xc + circPt.gety() , yc - circPt.getx());
	setPixel (xc - circPt.gety() , yc + circPt.getx());
	setPixel (xc + circPt.gety() , yc - circPt.getx());
	setPixel (xc - circPt.gety() , yc - circPt.getx());
}

};
int main(int argc,char** argv)
{
	screenPt sp;

	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowSize(400,400);
	glutInitWindowPosition(200,200);
	glutCreateWindow("My first OpenGl program");
	sp.Init();
	glutDisplayFunc(sp.circleMidpoint('y','t','y'));

	 glFlush();
	glutMainLoop();
	return 0;
}