so you lost some money . i am updating my knot vector, however. you are right. i don’t know much about knot vectors. i have read some about nurbs, but none of them contain a clear description on the knots. do you know such a text? i prefer onine ones, because it is not so easy for me to obtain printed ones.
the confusing part is that: the same thing happens when i am using cubic beziers. here what i am trying to draw:
i define nine points that forms a straight line:
and evaluation the curve as:
so simple isn’t it? the code should produce a straight line from (0,0) to (320,320). when i am using the number of points up to 8, the result is perfect (beginning from any point), however when this number reaches to 9, nothing is drawn… so stupid isn’t it?
and the nurbs one:
my knot vector is
using the same points, i evaluate the simple nurbs curve as:
gluNurbsCurve(pnurb , 18 , knot, 3 ,&point,9);
i don’t know if this kind of knot vector is correct, i found the logic by trial error, beginning from the 4 point curve… i am putting first n elements on the knot vector as zero and the second n as 1.0 and using the vector size as 2n where n is the number of points. it is again worked well upto 8 points, and failed at the 9th!!! i also tried to use smaller knots of the same form, but it also did’t worked…
i am agree and perfectly sure that this shouldn’t be a hardware bug, but what is it then? let’s say i am misusing the knots concept, but beziers must draw at least a straight line…
thank you for your help. I have the same code that is written years ago using PHIGS, that evaluates nurbs by code… i thought i won’t be have to add the same code to the OpenGL version… but it seems i should do that .
have a nice day. your help is really appreciated.