I have a problem with my NURBS function. I am trying to make a spline between 7 controlpoints with an order of 4.
I made bezier and non/ uniform b-spline that works great.

But my NURBS functions makes strange approximations.
In my display function i call makeNURBS() that is supposed to make the spline...but something goes wrong.
I would appreciate a little help since im kinda stuck. Below i have first pasted the important function, and then below again the whole cpp file is listed.

Hope for a little input Thanx in advance.
Regards TheBlackAdder

Code :
void makeNURBS(void)
{
	GLfloat NURBctrlpoints [7][4] = {
	{-10.,0.,0.,1.},
	{-10.,5.,0.,1.},
	{-5.,5.,0.,1.},
	{0.0,10.0,0.0,1.0},
	{5.,5.,0.,1.},
	{10.,5.,0.,1.},
	{10.,0.,0.,1.}};
 
	//GLfloat knots[]={0.0,0.0,0.0,0.0,1.0,2.0,3.0,4.0,4.0,4.0,4.0};
	GLfloat knots[]={0.0,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0};
	gluBeginCurve(theNurb);
	gluNurbsCurve(theNurb,11,knots,3,(GLfloat*)NURBctrlpoints,4,GL_MAP1_VERTEX_4);
	gluEndCurve(theNurb);
}
Here is the whole cpp file:
Code :
 
 
#include <GL/glut.h>
//#include <stdlib.h>
void makeBezier(void);
void makeUniformBSpline(void);
void makeNonUniformBSpline(void);
void makeNURBS(void);
 
GLfloat ctrlpoints [7][3] = {
	{-10.,0.,0.},
	{-10.,5.,0.},
	{-5.,5.,0.},
	{0.,10.,0.},
	{5.,5.,0.},
	{10.,5.,0.},
	{10.,0.,0.}};
 
 
	GLUnurbsObj * theNurb;
void init(void)
{
   theNurb = gluNewNurbsRenderer();
	glClearColor(1.0, 1.0, 1.0, 0.0);
   glShadeModel(GL_FLAT);
	gluNurbsProperty (theNurb, GLU_SAMPLING_METHOD, GLU_DOMAIN_DISTANCE);
	gluNurbsProperty (theNurb, GLU_U_STEP, 100);
}
 
void display(void)
{
   int i;
 
   glClear(GL_COLOR_BUFFER_BIT);
   glColor3f(0.0, 0.0, 0.0);
   glMatrixMode(GL_MODELVIEW);
	glLoadIdentity ();
	gluLookAt (0., 5., 1., 0., 5., 0., 0., 1., 0.);
 
	glPushMatrix();
 
/* The following code displays the control points as dots and line strip. */
   glPointSize(5.0);
   glColor3f(1.0, 0.0, 0.0);
   glBegin(GL_POINTS);
      for (i = 0; i < 7; i++) 
         glVertex3fv(&amp;ctrlpoints[i][0]);
   glEnd();
 
 
glColor3f(0.0, 0.0, 0.0);
glBegin(GL_LINE_STRIP);
    for (i = 0; i < 7; i++) 
      glVertex3fv(&amp;ctrlpoints[i][0]);
glEnd();
 
	glColor3f(1.0,0.0,0.0);
	makeBezier();
	glColor3f(0.0,1.0,0.0);
	makeUniformBSpline();
	glColor3f(0.0,0.0,1.0);
	makeNonUniformBSpline();
	glColor3f(0.5,0.5,0.5);
	makeNURBS();
 
   glPopMatrix();
   glFlush();
}
 
void makeBezier(void)
{
   	GLfloat knots[]={0.0,0.0,0.0,0.0,1.0,1.0,1.0,1.0};
	GLfloat bezierCurve[]={
		ctrlpoints[0][0],ctrlpoints[0][1],ctrlpoints[0][2],
		ctrlpoints[1][0],ctrlpoints[1][1],ctrlpoints[1][2],
		ctrlpoints[2][0],ctrlpoints[2][1],ctrlpoints[2][2],
		ctrlpoints[3][0],ctrlpoints[3][1],ctrlpoints[3][2],
 
		ctrlpoints[3][0],ctrlpoints[3][1],ctrlpoints[3][2],
		ctrlpoints[4][0],ctrlpoints[4][1],ctrlpoints[4][2],
		ctrlpoints[5][0],ctrlpoints[5][1],ctrlpoints[5][2],
		ctrlpoints[6][0],ctrlpoints[6][1],ctrlpoints[6][2]	
	};
 
	gluBeginCurve(theNurb);
		gluNurbsCurve(theNurb,8,knots,3,bezierCurve,4,GL_MAP1_VERTEX_3);
	gluEndCurve(theNurb);
 
	gluBeginCurve(theNurb);
		gluNurbsCurve(theNurb,8,knots,3,bezierCurve+4*3,4,GL_MAP1_VERTEX_3);
	gluEndCurve(theNurb);
}
 
void makeUniformBSpline(void)
{
   	GLfloat knots[]={0.0,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0};
	gluBeginCurve(theNurb);
	gluNurbsCurve(theNurb,11,knots,3,(GLfloat*)ctrlpoints,4,GL_MAP1_VERTEX_3);
	gluEndCurve(theNurb);
}
void makeNonUniformBSpline(void)
{
	GLfloat knots[]={0.0,0.0,0.0,0.0,1.0,2.0,3.0,4.0,4.0,4.0,4.0};
 
	gluBeginCurve(theNurb);
	gluNurbsCurve(theNurb,11,knots,3,(GLfloat*)ctrlpoints,4,GL_MAP1_VERTEX_3);
	gluEndCurve(theNurb);
}
 
void makeNURBS(void)
{
	GLfloat NURBctrlpoints [7][4] = {
	{-10.,0.,0.,1.},
	{-10.,5.,0.,1.},
	{-5.,5.,0.,1.},
	{0.0,10.0,0.0,1.0},
	{5.,5.,0.,1.},
	{10.,5.,0.,1.},
	{10.,0.,0.,1.}};
 
	//GLfloat knots[]={0.0,0.0,0.0,0.0,1.0,2.0,3.0,4.0,4.0,4.0,4.0};
	GLfloat knots[]={0.0,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0};
	gluBeginCurve(theNurb);
	gluNurbsCurve(theNurb,11,knots,3,(GLfloat*)NURBctrlpoints,4,GL_MAP1_VERTEX_4);
	gluEndCurve(theNurb);
}
 
void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (w <= h)
      gluOrtho2D (-12.0, 12.0, -12.0*(GLfloat)h/(GLfloat)w, 
               12.0*(GLfloat)h/(GLfloat)w);
   else
      gluOrtho2D(-12.0*(GLfloat)w/(GLfloat)h, 
               12.0*(GLfloat)w/(GLfloat)h, -12.0, 12.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}
 
void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
//         exit(0);
         break;
   }
}
 
int main(int argc, char** argv)
{
   glutInit(&amp;argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display);
   glutReshapeFunc(reshape);
   glutKeyboardFunc (keyboard);
   glutMainLoop();
   return 0;
}