Jan. 9, 2003 03:04:23
Can anyone explain how the PrimitiveSplit Sop works? I don't see any influence on the input geometry by this sop. Even after reading the document, I don't really get what this sop does.
Thanks in advance.
Jan. 9, 2003 11:57:36
In Houdini the shading of polygons is determined by the point connectivity. If the vertices of two polygons share a point, they will shade smoothly. This is also used elsewhere, for example in the Subdivision and in the Triangle Strip methods.
This can be demonstrated with:
Got to Attributes, change it to Add Color, set the fields to
1 $PR==0 1
You know have a purple cube with one white face on primitive 0.
Add a tristrip. You now have totally different colours as Houdini merged some of the side polygons with the white one. To avoid this, we have to tell Houdini that the primitives should not be connected in the tristrip.
Do this by, after the primitive, adding PrimitiveSplit. Set the attribute to Cd. Note that you now have unique points along the edge where the colours change.
Add a tristrip to this - it will match your original.
You can also use this to split the points where materials change by using vm_surface as the attribute name.
Jan. 10, 2003 06:06:58
thanks so much, Brask!!
I am not quite clear about the vm_surface attribute u mentioned, what data does this attribute store? And which OP add this attribute to primitive?
One more question…Can u explain the usage of the meta-surface weight in primitive sop?
Jan. 10, 2003 12:11:15
The vm_surface attribute is added by the shader SOP. It contains the black magic to describe the shader to apply to each primitive.
The primitive meta weight option allows you to change the weight of metaballs. Put down a metaball sop, append a primitive with this option on, and you will see that you can change the weight with it.