Flow ofExecution

#include<windows.h>
#include<gl/gl.h>
#include<gl/glu.h>
#include<gl/glut.h>
#include<cmath>

#define GL_PI 3.1415

GLfloat xRot =0.0f;
GLfloat yRot =0.0f;

BOOL bCull=false;
BOOL bDepth=false;
BOOL bOutline=false;

void ProcessMenu(int value)
{
	switch (value)
	{
	case 1:
		bDepth=!bDepth;
		break;
	case 2:
		bCull=!bCull;
		break;
	case 3:
		bOutline=!bOutline;
		break;
	default:
		break;
	}
	glutPostRedisplay();
}
void initScene()
{
	GLfloat x,y,angle;
	int iPivot=1;

	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

	if(bCull)
			glEnable(GL_CULL_FACE);
	else
			glDisable(GL_CULL_FACE);

	if(bDepth)
			glEnable(GL_DEPTH_TEST);
	else
			glDisable(GL_DEPTH_TEST);

	if(bOutline)
			glPolygonMode(GL_BACK,GL_LINE);
	else
			glPolygonMode(GL_BACK,GL_FILL);

	glPushMatrix();
	glRotatef(xRot,1.0f,0.0f,0.0f);
	glRotatef(yRot,0.0f,1.0f,0.0f);

	glBegin(GL_TRIANGLE_FAN);
		
		glVertex3f(0.0f,0.0f,75.0f);

		for(angle=0.0f;angle<=2.0f*GL_PI;angle+=GL_PI/8.0f)
		{
			x=50.0f*sin(angle);
			y=50.0f*cos(angle);

			if(iPivot%2==0)
							glColor3f(1.0f,0.0f,0.0f);
			else
							glColor3f(0.0f,1.0f,0.0f);

			glVertex2f(x,y);
			iPivot++;
		}
	glEnd();
	
	glBegin(GL_TRIANGLE_FAN);
			glVertex2f(0.0f,0.0f);

			for(angle=0.0f;angle<=2.0f*GL_PI;angle+=GL_PI/8.0f)
			{
				x=50.0*sin(angle);
				y=50.0f*cos(angle);

				if(iPivot%2==0)
								glColor3f(1.0f,0.0f,0.0f);
				else
								glColor3f(0.0f,1.0f,0.0f);
				 iPivot++;

				 glVertex2f(x,y);
			}
	glEnd();
	glPopMatrix();

	glutSwapBuffers();
}
void setupRC()
{
	glClearColor(0.0f,0.0f,0.0f,1.0f);

	glShadeModel(GL_FLAT);

	glFrontFace(GL_CW);
}
void SpecialKeys(int key, int x, int y)
	{
	if(key == GLUT_KEY_UP)
		xRot=xRot- 5.0f;

	if(key == GLUT_KEY_DOWN)
		xRot= xRot+ 5.0f;

	if(key == GLUT_KEY_LEFT)
		yRot =yRot- 5.0f;

	if(key == GLUT_KEY_RIGHT)
		yRot =yRot+ 5.0f;

	if(key > 356.0f)
		xRot = 0.0f;

	if(key < -1.0f)
		xRot = 355.0f;

	if(key > 356.0f)
		yRot = 0.0f;

	if(key < -1.0f)
		yRot = 355.0f;

	// Refresh the Window
	glutPostRedisplay();
	}


void ChangeSize(int w, int h)
	{
	GLfloat nRange = 100.0f;

	// Prevent a divide by zero
	if(h == 0)
		h = 1;

	// Set Viewport to window dimensions
    glViewport(0, 0, w, h);

	// Reset projection matrix stack
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	// Establish clipping volume (left, right, bottom, top, near, far)
    if (w <= h) 
		glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
    else 
		glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);

	// Reset Model view matrix stack
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	}
void handleKeyPress(unsigned char key,int x,int y)
{
	switch(key)
	{
	case 27:
		exit(0);
	case 32:
		exit(0);
	}
}
int main(int argc,char **argv)
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
	glutCreateWindow("I love GLUT");

	glutCreateMenu(ProcessMenu);
	
	glutAddMenuEntry("Toggle depth test",1);
	glutAddMenuEntry("Toggle cull backface",2);
	glutAddMenuEntry("Toggle outline back",3);
	glutAttachMenu(GLUT_RIGHT_BUTTON);
	
	glutSpecialFunc(SpecialKeys);
	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(initScene);
	
	setupRC();
	glutKeyboardFunc(handleKeyPress);
	
	glutMainLoop();

	return 0;
}