Sign in to follow this  

Problem in Circle drawing using glNurbsCurve

This topic is 4106 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi , I have a hexagon gving me six control points.I need to draw a circle using glNurbsCurve. Following is a snippet of my code : void drawNurbsCurve(float** ObjectCtrPts , int iTotalCtrlPts) { //GLUnurbsObj *pNurb = NULL; int i = 0 ; //int iKnotCount = ORDER + iTotalCtrlPts ; int iKnotCount = 13; int kStride = 2; GLfloat Knots[13] = {0.0,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0,11.0,12.0} ; { glNewList(3, GL_COMPILE); // Begin the NURB definition glColor3f(0.2,0.8,0.5); gluBeginCurve(pNurb); //Enable the following glEnable(GL_MAP1_VERTEX_3); // Send the Non Uniform Rational BSpline gluNurbsCurve(pNurb, 13, Knots, kStride, &ObjectCtrPts[0][0] , 4, GL_MAP1_VERTEX_3); gluEndCurve(pNurb); glBegin(GL_POINTS); glColor3f(1.0,1.0,1.0); glVertex3f(0.0f, 0.0f , 0.0f); glEnd(); glEndList(); } I am passing Object control points as follows: ObjCtrPts[][] = { 1.0 , 0.0 ; 0.5, sqrt(3)/4 ; -0.5, sqrt(3)/4; - 1.0 , 0.0 ; -0.5, -sqrt(3)/4}; 0.5, -sqrt(3)/4 } And I am using function call as : gluNurbsCurve(pNurb, 13, Knots, kStride, &ObjectCtrPts[0][0] , 4, GL_MAP1_VERTEX_3); Where my order is 4 , num of knots is 13 ( since control points are 9, for drawing a circle) and knotcount is 13. I am using GL_MAP1_VERTEX_3 RESULT : Getting two perpendicular lines meeting at coordinate (0.0f , 0.0f) i.e at origin. When i use GL_MAP_VERTEX_4 I get a straigh line starting from Control point number 1 and goes out of screen(viewport). I want to get a circle.Where am I going wrong.I searched the RED Book and other sites on google but could not get any help.Hope I will be fortunate this time.

Share this post


Link to post
Share on other sites
I had played with nurb surface rendering quite some time ago . The following points may be of some help.

Try the following :
1. You are trying to compile gluNurbCurve into a display list.
Try calling in directly in the main render loop.
This is to check if the control points you have supplied are correct.
If they still do not render correctly there may be a problem with the
control points.

2. When i had to compile a gluNurbs* into a display lists , i first set the
rendering call back for the nurbs renderer .. and then call the
gluNurbsSurface() function. If you are not aware of callbacks ..the redbook
explains them .. shouldnt be a problem. my nurbs surface rendering calls then
get compiled properly into a display list and works properly with the callback
mechanism.

you also need to look into the call gluNurbsProperty() function call that helps you set the quality with which the nurb is to tesselated.

Good Luck

Share this post


Link to post
Share on other sites

This topic is 4106 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this