RenderMan & RISpec, Curve Normals?

comp.graphics.rendering.renderman - RenderMan interface & shading language.


RenderMan & RISpec >> Curve Normals?

by noizFACTORY@gmail.com » Thu, 29 May 2008 14:11:45 GMT

Hello all,

I just started getting into renderman and was interested in doing a
test for using curves as textured ribbons. While that part wasn't so
hard to figure out, what is kind of bothering me is that the curves
always seem to face the camera (like sprite particles do).

While this is expected, it won't let me achieve the desired effect. I
searched through the net for info and what I learnt was that I need to
export surface normals data for the curves to orient them correctly at
render time. Is that possible for curves? If so, how would I go about
doing that?

I would really appreciate it if anyone can point me in the right
direction (relevant reading materials or papers are also fine).

Best,
Sachin
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RenderMan & RISpec >> Curve Normals?

by Olivier3001 » Thu, 29 May 2008 20:53:32 GMT


On May 29, 2:11 am, " XXXX@XXXXX.COM " < XXXX@XXXXX.COM >


Just like other primitives, you attach the "N" variable to it:
Curves "cubic" [4] "nonperiodic"
"P" [-0 0 0 -0.2 1 0 0.2 2 0 -0.1 3 0]
"N" [0.3 0 -1 0.7 0 -1]

Note that N is varying, not vertex.
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RenderMan & RISpec >> Curve Normals?

by noizFACTORY@gmail.com » Fri, 30 May 2008 17:15:10 GMT


Thank you for the reply Olivier.

For a curve system generated by a package like Shave and A Haircut or
Maya Hair, how do you think I can go about attaching the N variable to
the output curves? Would I do that using the delightGeoAttributes node
(as I'm using 3dfm)?
I'm looking to replicate the following method that's suggested in the
MayaMan help docs:

The special name Width is specified then the curve is given width data
that will change over the length of the curve. If you use the special
name Normal then the curve is given normal data. All other names are
passed unfiltered. Vector arrays, other than Normal, are passed as an
array of colors which is convenient when the data name is Cs,
conversion to any other data type is trivial to handle in the shader.

To set width and normal data on a open nurbs curve with 5 control
points execute a mel script like this:

setAttr MayaManAttributes1.MayaManCurveWidth -type doubleArray 5 1 2
3 2 1
setAttr MayaManAttributes1.MayaManCurveNormal -type vectorArray 5 0 1
0 0 0 1 0 -1 0 0 0 -1 0 1 0

-Sachin
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