/*
 *  surface.c
 *  This program draws a NURBS surface in the shape of a 
 *  symmetrical hill.
 */
#include <GL/gl.h>
#include <GL/glu.h>
#include <stdlib.h>
#include "glaux.h"

GLfloat ctlpoints[4][4][3];

GLUnurbsObj *theNurb;

/*
 *  Initializes the control points of the surface to a small hill.
 *  The control points range from -3 to +3 in x, y, and z
 */
void init_surface(void)
{
    int u, v;
    for (u = 0; u < 4; u++) {
	for (v = 0; v < 4; v++) {
	    ctlpoints[u][v][0] = 2.0*((GLfloat)u - 1.5);
	    ctlpoints[u][v][1] = 2.0*((GLfloat)v - 1.5);

	    if ( (u == 1 || u == 2) && (v == 1 || v == 2))
		ctlpoints[u][v][2] = 3.0;
	    else
		ctlpoints[u][v][2] = -3.0;
	}
    }				
}				
			
/*  Initialize material property and depth buffer.
 */
void myinit(void)
{
  

    GLfloat mat_diffuse[] = { 0.7, 0.7, 0.7, 1.0 };
    GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat mat_shininess[] = { 100.0 };

    glClearColor (0.0, 0.0, 0.0, 1.0);
    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glDepthFunc(GL_LESS);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_AUTO_NORMAL);
    glEnable(GL_NORMALIZE);

    glClearColor(0.1,0.3,0.8,0.0);    /*  background color */
    glClear(GL_COLOR_BUFFER_BIT);

    init_surface();

    theNurb = gluNewNurbsRenderer();
    gluNurbsProperty(theNurb, GLU_SAMPLING_TOLERANCE, 25.0);
    gluNurbsProperty(theNurb, GLU_DISPLAY_MODE, GLU_FILL);
}

void display(void)
{
    GLfloat knots[8] = {0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0};

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glPushMatrix();
    glRotatef(330.0, 1.,0.,0.);
    glScalef (0.5, 0.5, 0.5);

    gluBeginSurface(theNurb);
    gluNurbsSurface(theNurb, 
	    8, knots,
	    8, knots,
	    4 * 3,
	    3,
	    &ctlpoints[0][0][0], 
	    4, 4,
	    GL_MAP2_VERTEX_3);
    gluEndSurface(theNurb);
        
    glPopMatrix();
    glFlush();
}

void myReshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective (45.0, (GLdouble)w/(GLdouble)h, 3.0, 8.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef (0.0, 0.0, -5.0);
}

/*  Main Loop 
 */
int main(int argc, char** argv)
{
    auxInitDisplayMode (AUX_SINGLE | AUX_RGB);
    auxInitPosition (0, 0, 500, 500);
    auxInitWindow (argv[0]);
    myinit();
    auxReshapeFunc (myReshape);
    auxMainLoop(display);
}