#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>

/*
 * nonuniform rational B-spline circle
 *
 * 4/7/03 pjf
 *
 */


#define NP 9
#define NKNOTS 12
#define ORDER 3
#define STRIDE 4

GLfloat p[9][4] = {{ 0.5,0,0,1 },
                   {0.5,0.5,0,.707},
                   {0,0.5,0,1},
                   {-0.5,0.5,0,.707},
                   {-0.5,0,0,1},
                   {-0.5, -0.5, 0,.707},
                   {0, -0.5, 0,1},
                   {0.5, -0.5, 0,.707},
                   {0.5,0,0,1}};


GLfloat knots[12] = { 0,0,0,1,1,2,2,3,3,4,4,4 };

GLUnurbsObj *nurb;

int ww,hh;


void CALLBACK nurbsError(GLenum errorCode) {
 const GLubyte *s = gluErrorString(errorCode);
 fprintf(stderr,"NURBS error: %s\n",s);
 exit(-1);
 }


/* display callback */
void display() {
 int i;
 glClear(GL_COLOR_BUFFER_BIT);
 glColor3f(1.0,1.0,1.0);

 gluBeginCurve(nurb);
 gluNurbsCurve(nurb,NKNOTS,knots,
               STRIDE,&p[0][0],ORDER,GL_MAP1_VERTEX_4);
 gluEndCurve(nurb);

 // now draw boxes around control points
 for (i=0;i<NP;i++) {
  float colors[4][3] = { { 1.0,0.0,0.0},{0.0,1.0,0.0},{0.0,0.0,1.0},{0.5,0.5,0.5}};
  GLfloat x = p[i][0]/p[i][3] - 0.02;
  GLfloat y = p[i][1]/p[i][3] - 0.02;
  GLfloat z = p[i][2]/p[i][3];
  glColor3f(colors[i%4][0],colors[i%4][1],colors[i%4][2]);
  glBegin(GL_LINE_LOOP);
   glVertex3f(x,y,z);
   glVertex3f(x+0.04,y,z);
   glVertex3f(x+0.04,y+0.04,z);
   glVertex3f(x,y+0.04,z);
  glEnd();
  }
 glFlush();
 }


/* called initially (before first call to display()) and whenever the
   window is resized */
void reshape(int w, int h) {
  fprintf(stderr,"reshape: new size %d x %d.\n",w,h);
  // must update viewport and clipping planes
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-1.0,1.0,-1.0,1.0,-1.0,1.0);
  glMatrixMode(GL_MODELVIEW);
  ww=w; hh=h;
}

void mouse(int btn, int state, int x, int y) {
 }

void motion(int x, int y) {
 }
 
void init(void) {
 int i;
 /* nothing to do! */
 nurb = gluNewNurbsRenderer();
 // could use gluNurbsProperty() to change the NURB's settings here
 gluNurbsProperty(nurb,GLU_SAMPLING_TOLERANCE,1.0);

 for(i=0;i<NP;i++) { // weight the points
  p[i][0]  *= p[i][3];
  p[i][1]  *= p[i][3];
  p[i][2]  *= p[i][3];
  }
 }

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutCreateWindow(argv[0]);
    glutReshapeFunc(reshape);
    glutDisplayFunc(display);
    glutMouseFunc(mouse);
    glutMotionFunc(motion);
    init();
    glutMainLoop();
    return 0;
}