#include "GL/glut.h"
#include <stdlib.h>
#include <string.h>

#define TIMER 33



static float xrot;

#define TOGGLE_ROTATE 1
#define STEP_ROTATE 2
static int rotate, step;

static int ext10Available = 0;


GLUquadric *quad;


void drawObj ()
{
    glPushMatrix ();
    glTranslatef (0., 0., 2.);
    gluDisk (quad, 0., .5, 18, 1);
    glPopMatrix ();

    gluCylinder (quad, .5, .5, 2., 18, 8);

    glPushMatrix ();
    glScalef (1., 1., -1.);
    gluDisk (quad, 0., .5, 18, 1);
    glPopMatrix ();
}


static void display( void )
{
    int i;

    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity ();
    gluLookAt (0., 0., 5.,
               0., 0., 0.,
               0., 1., 0.);

    glRotatef (xrot, 1., 0., 0.);
    glTranslatef (0., 0., -1.);

    for (i=0; i<2; i++) {
        glPushMatrix ();
        glTranslatef ((i?.6:-.6), 0., 0.);

        glColor3f (1., 1., 1.);
        drawObj();

        glPushAttrib (GL_ALL_ATTRIB_BITS);
        if (i==0) {
			if (ext10Available) {
				/* Use OpenGL 1.0 polygon offset extension */
#ifdef GL_EXT_polygon_offset
				glEnable (GL_POLYGON_OFFSET_EXT);
				glPolygonOffsetEXT (1., 1./(float)0x10000);
#endif /* GL_EXT_polygon_offset */
			}
        }
        else {
            /* Use OpenGL 1.1 polygon offset feature */
#ifdef GL_VERSION_1_1
            glEnable (GL_POLYGON_OFFSET_FILL);
            glPolygonOffset (1., 1.);
#endif /* GL_VERSION_1_1 */
        }
        glPolygonMode (GL_FRONT_AND_BACK, GL_FILL);
        glEnable (GL_LIGHTING);
        glColor3f (.2, .2, 1.);
        drawObj();
        glPopAttrib ();

        glPopMatrix ();
    }

    glFlush();
    glutSwapBuffers();
}

void reshape(int w, int h)
{
    glViewport (0, 0, w, h);       
    glMatrixMode (GL_PROJECTION);  
    glLoadIdentity ();
    gluPerspective (50., (float)w/(float)h, 1., 20.);
}

static void cbMainMenu (int value)
{
    if (value == 99) {
        exit (0);
    }
    else if (value == TOGGLE_ROTATE) {
        rotate = !rotate;
    }
    else if (value == STEP_ROTATE) {
        step = 1;
    }
}


static void timer (int value)
{
    if (rotate || step) {
        step = 0;
        xrot += 1.f;
        if (xrot > 360.f) xrot -= 360.f;

        glutPostRedisplay ();
    }
    
    glutTimerFunc (TIMER, timer, 0);
}


static void init ()
{
    int mainMenu;
    const GLubyte *str;

    str = glGetString (GL_EXTENSIONS);
    ext10Available = (strstr((const char *)str, "GL_EXT_polygon_offset") != NULL);
    
    xrot = 0.;

    glDisable (GL_DITHER);
    glEnable (GL_DEPTH_TEST);
    glPolygonMode (GL_FRONT_AND_BACK, GL_LINE);


    {
        GLfloat pos[4] = {3., 5., 2., 1.};
        GLfloat white[4] = {1., 1., 1., 1.};
        GLfloat black[4] = {0., 0., 0., 0.};

        /* Set up light1 */
        glDisable (GL_LIGHTING);
        glEnable (GL_LIGHT1);
        glLightfv (GL_LIGHT1, GL_POSITION, pos);
        glLightfv (GL_LIGHT1, GL_DIFFUSE, white);
        glLightfv (GL_LIGHT1, GL_SPECULAR, black);

        /* ambient and diffuse will track glColor */
        glEnable (GL_COLOR_MATERIAL);
        glColorMaterial (GL_FRONT, GL_AMBIENT_AND_DIFFUSE);
        glMaterialfv (GL_FRONT, GL_SPECULAR, black);
    }


	quad = gluNewQuadric ();

    glutDisplayFunc (display); 
    glutReshapeFunc (reshape);
    glutTimerFunc (TIMER, timer, 0);
    
    mainMenu = glutCreateMenu (cbMainMenu);
    glutAddMenuEntry ("Toggle Rotate", TOGGLE_ROTATE);
    glutAddMenuEntry ("Step Rotate", STEP_ROTATE);
    glutAddMenuEntry ("Quit", 99);
    glutAttachMenu (GLUT_RIGHT_BUTTON);
    rotate = 1;
    step = 0;
}

void main(int argc, char** argv)
{
    glutInit (&argc,argv);
    glutInitDisplayMode (GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE); 
    glutInitWindowSize (300,300);
    glutInitWindowPosition (0,0); 
    glutCreateWindow ("Polygon Offset: 1.0 versus 1.1");

    init ();

    glutMainLoop ();
}