Re: [PyOpenGL-Users] Coloring Nurb Surface

[Michka P. <mic...@gm...>]

Thanks for answering

Dirk :
generally the most generic and efficient way for that is to use glTexGen to
turn
your height into a texture coordinate and use a 1D texture for the colors to
interpolate between. This allows you to fully specify the color that are
interpolated and also enables you to do non-linear mappings (e.g. have a
bright
band at a specific height). Give it a try!

Ian Mallett :
I'd use a vertex shader.


The two ideas seem okay for me, but I think I am stuck : I have no influence
on the nurb displayed, because I don't know how to modify it before it is
displayed. (or after).

I tried a few things :

1) I used gluNurbsProperty(nurb, GLU_NURBS_MODE, GLU_NURBS_TESSELLATOR) and
gluNurbsCallback(nurb,GLU_NURBS_COLOR,color). I was able to print the colors
of every point in the callback function. But I can not modify them. So why
does this function exist ? And as the nurb is now tesselated, how can I
display it ?

2) I used gluNurbsSurface(nurb, knots, knots, ctrlpts, GL_MAP2_COLOR_4). In
the callback documentation for gluNurbsCallback() I have found :

This callback is effective only when the user provides  a  color map
(*GL**_**MAP1**_**COLOR**_**4* or *GL**_**MAP2**_**COLOR**_**4*).
``color'' contains four components: R,G,B,A

So where can I provide my own color map ? Documentation never says anything
about this.

My ideas :

1) I could subdivide my big nurb surface in a lot of little nurb patches,
and put a colored texture on it. Like the typical molehill.py tutorial you
can find everywhere. I think it is quite the same as Dirk's idea ?

2) I could rewrite everything with my own polygons, where I can define the
colors myself. Will not be as smooth as it is now, but should work.

Michka Popoff