Hi!

I have a bunch of non-connected primitives. Some have their normals in the wrong direction and I'm trying to change that.

I tried tranfering the prim normals from another mesh to this one with a wrangle (xyzdist), but the normals just dont change. I also tried setting the point normals and transfer these point normals to my primitives (attribute transfer sop) but it still doesn't change.

For fun, I used a primitive wrangle and did:


…but it still doesn't modify the prim normals. Why is that?

-Olivier

Hi, Olivier,

I just tried the wrangle you quoted and it works for me (looking at the geo spreadsheet). However, there seems to be a bug in the normal display in 3d-view, those don't get updated. They don't get updated when you use a normal-node and invert primitive normals. So you may have to use the spreadsheet for the moment until the bug is fixed (I filed it).


Marc

Ok, so I was looking in the viewport to see if my prim normals changed and didn't notice any change. But if I look in the geometry spreadsheet, it does change!

It's all good!

-Olivier

you can't change geometric primitive normals, they are defined by winding of the geometry (making primitive v@N won't affect them, but it can be used for shading)
so if you want to flip or reverse normals of a certain polygon group, use Reverse SOP (also possible with Primitive SOP if you set Poly/Hull/Vertex to Reverse)

lso Poly Doctor or Facet SOP have options to fix winding of the olygons (orientation) in case you have connected polygons with mixed winding

> making primitive v@N won't affect them, but it can be used for shading

… well, according to the geo spreadsheet, you can change them.

Marc

malbrecht
> making primitive v@N won't affect them, but it can be used for shading

… well, according to the geo spreadsheet, you can change them.

Marc

yes, you can and as mentioned that attribute and values will be used in shading as shading normals similar to vertex and point v@N
but having primitive v@N attribute will not change implicit geometric primitive normal that is defined by topology, in any software for that matter, Houdini uses left handed winding rule

The word “implicit” is the most important in your statement:
The 3d viewport “display primitive normals” does not mention “implicit” (nor does it say “defined by winding order of points in the primitive”), so one must assume that the same “attribute quality” as with point normals or vertex normals is meant, not an implicit (as in “NOT attribute”) quality.

It may not be a “bug”, but it clearly looks like an irritating if not misleading description in the UI.

Marc