BUG: normals flippin' out

Hi McNeel team,

Normals direction is very important for our work. And we use special backface color on most of the time while modeling to see normals direction, open faces, etc.

I’ve noticed many tools in RHino think that normals are not important and they seem to somethings decide normal direction in new surfaces created to be completely arbitrary. And then there are tools that are outright disrespectful and flip the normals of what’s already there, like this _Cap command.

That’s a big no-no. OK?



what happens on that model if you explode all then immediately join all?

That won’t fix it. Keep in mind in this case the model is still an open polysurface before and after the _Cap command.

Here a similar file that you can use to replicate the problem.

cap_flipping_bug_gf_201027.3dm (402.1 KB)

I’m just making sure that when you do explode and join that the normals are at least unified in one direction on the part.

As it sits, we do not have a good way to force all the normals to be “out” on open surfaces or polysurfaces by default. Closed polysurfaces SHOULD be out by default, are you seeing cases where they are not?

they are

I disagree, I’m not asking for an ‘out’ or ‘in’ of an open polysurface. I understand that a computer does not know what I expect to be ‘out’ or ‘in’.

All I’m asking:

“If I have an input polysurface, and I ask you (Rhino) to cap its planar holes just pay attention at its normals and DO NOT change them”

This has to be a simple, non controversial, non conflicting code change.

In general I see many tools that pay absolutely no attention to existing input surfaces’ normals, and I 'd argue they always should. NetworkSrf, and BlendSrf have similar limitations AFAIK.


Hi, Gustavo,

I’ve looked at cap_flipping_bug_gf_201027.3dm in Rhino 7. You are correct that Cap is incorrectly reversing the orientation of the input polysurface. Cap should preserve the orientation of the input polysurface and add caps with compatible orientations. This is a bug and I’ve added an issue to our bug tracking system so it will get fixed.


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Thx! We are a good team Dale!