GLUT Animation example

#include <GL/freeglut.h>

int lastTime;
int delta;
float rotator = 0.0f;

void ReSizeGLScene(int width, int height)             // Resize And Initialize The GL Window
{
    if (height == 0)                              // Prevent A Divide By Zero By
    {
        height = 1;                           // Making Height Equal One
    }

    glViewport(0, 0, width, height);                    // Reset The Current Viewport
    glMatrixMode(GL_PROJECTION);                        // Select The Projection Matrix
    glLoadIdentity();                           // Reset The Projection Matrix

    // Calculate The Aspect Ratio Of The Window
    gluPerspective(45.0f, (GLfloat) width / (GLfloat) height, 0.1f, 100.0f);

    glMatrixMode(GL_MODELVIEW);                     // Select The Modelview Matrix
    glLoadIdentity();                           // Reset The Modelview Matrix
}

void renderScene(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushMatrix();
    glTranslatef(0, 0, -3);
    glRotatef(rotator, 0, 1, 0);
    glRotatef(rotator / 4, 0, 0, 1);
    glBegin(GL_TRIANGLES);
    glColor3f(0, 1, 0);
    glVertex3f(-.5, -.5, -.5);
    glVertex3f(.5, .5, -.5);
    glVertex3f(-.5, .5, -.5);

    glColor3f(1, 0, 0);
    glVertex3f(.5, -.5, -.5);
    glVertex3f(.5, .5, .5);
    glVertex3f(.5, -.5, .5);
    glEnd();
    glBegin(GL_QUADS);
    glColor3f(1, 1, 0);
    glVertex3f(.5, -.5, .5);
    glVertex3f(.5, -.5, -.5);
    glVertex3f(-.5, -.5, -.5);
    glVertex3f(-.5, -.5, .5);
    glEnd();
    glPopMatrix();
    rotator = rotator + delta / 10.0f;
    glutSwapBuffers();
    glFlush();
}
void onIdle()
{
    int time;
    time = glutGet(GLUT_ELAPSED_TIME);
    delta = time - lastTime;
    lastTime = time;
    //Sleep(50);
    glutPostRedisplay();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(320, 320);
    glutCreateWindow("OpenGL Renderer");
    glutDisplayFunc(renderScene);
    glutReshapeFunc(ReSizeGLScene);
    glutIdleFunc(onIdle);
    gluPerspective(45, 1, 2, 10);

    glEnable(GL_DEPTH_TEST);

    glutMainLoop();
    return 0;
}