I have a little scene set-up that has a ball being broken in bits from the top to bottom. When I render though, you can see all the fracture cracks. I read somewhere you could use the normals from the original non-fractured ball on the fractured one during render time, but how do I set this up?

Thanks for any assistance!

Try the attribute transfer SOP, plug in your fractured geometry as target and the non fractured one as source and play around with the transfer parameters. be careful though, you most certainly want to transfer the attributes on start frame, so do this before sending the fractured geometry to the DOP network if you're simulating it.

cheers,
Abdelkareem

Thanks - I'll give that a try!

Another thing you could try is calculating point normals before fracture (select Point SOP -> Add Normals), and untick any “recalculate point normals” or “consolidate” -sounding checkboxes in operations after that.

eetu.

Thanks. I got a set-up that seems to work quite well now. I got a point SOP removing the fracture normals and a point SOP adding the normals from a highres unbroken version, then the atrib-transfer feeding the hi-res ones to the fracture ones. Its not perfect, but its much better.

The thing I'm a bit confused about it that I thought 3D apps had either point normals (Maya) or polygon normals (LW) but there seems to be both in houdini, so which does Mantra use to shade the object?

it's a litle bit difrent.

points don't have normals, vereces do!
faces have normals but they do not effect the shading the vertex normals do.
the “point normals” in houdini (if you can call them that)basicly effect the vertex normals of the object and thats what you see renderd.

Thanks for the explanation Tamis!

So if understand this right, without vertex normals, Mantra would not be able to compute shading such as ambient and diffuse, but would still see the geometry defined in the polygon face normals?

If there is a face, then you can say that that face always has 4 verteces.
if there is a vertex then that vertex ALWAYS has a vertex normal.

if you don't use the normals in houdini then those verteces inherit the Normal component of the face the vertex is part of.

these components always excist:
Face
Face Normal
Verteces
Verteces Normals

Thanks again!

Your explanation has cleared things up in my head

http://odforce.net/wiki/index.php/PointVsVertex [odforce.net]