View Full Version : nurbs trouble

03-31-2001, 06:48 AM
Hi, i'm playing with nurbs surfaces using (glu functions) and facing two problems :

1. I haven't found any example of how to texture it (it works well without textures), i'd really appreciate one, because glu always send me error messages when i'm calling gluNurbsSurface (..., GL_MAP2_TEXTURE_COORD_2); - in fact i just don't know what parameters to give, knots, control vertices...

2. When exporting nurbs from 3ds Max, it works well with 4x4 surfaces (8 & 8knots), but when it comes to larger surfaces, max doesn't give me enough knots for glu, for example 10 and 10 knots on a 6x6 surface, whereas glu requires 12. I tried to 'complete' the missing knots, but what i tried didn't really worked http://www.opengl.org/discussion_boards/ubb/wink.gif

I searched a lot over the web, but couldn't find anything, so you're my only hope http://www.opengl.org/discussion_boards/ubb/biggrin.gif
Thanks a lot.

04-07-2001, 02:50 AM
I'd be interested by a bit of source code showing how to tessellate nurbs surfaces, without using glu functions (ok, this is no more opengl related but i have to find a way)...
Thank you

04-25-2001, 09:44 AM
Are you sure, you have the same order for both nurbs? glu uses (number of controlpoints) + (order) = (number of knots). If your larger surface were a cubic nurbs (order=4), then glu only requires 10 knots, maybe you mixed up the number of controlpoints (4 resp. 6) with the order (4 in both cases).

Though it's pretty late, i hope i could give you an idea.

04-25-2001, 11:41 AM
I agree with knut.

Are you trying to use all the control points from the MAX file as the control points of your patch. I your are, then you've created a surface with a higher order than a cubic nurbs patch.

Make smaller 4*4 patches from the the array of points given from the MAX file. This will work because NURBS have C2 continuity, the control points of a series of contiguous patchs share control points. In 2D, a cubic NURBS curve with 6 control points would be created from 3 NURBS curves with points [0123], [1234] and [2345].

Someone posted the source for a bezier tesselator on the boards a couple of weeks ago.