Inverted normals


#1

Has anybody else seen this problem I am getting?

Some of my objects are coming inworld inside-out, I set the normals as they should be in Blender, yet when I upload them into hifi they are all inside out, the outside is non existent, I can see thru to the inside which shouldnt render at all.

If I go back to blender and reverse the normals so that it is completely wrong according to the render and the normals markers, then upload it, it comes in reversed and looks right. I cant work like this there must be something wrong maybe a setting or something.

This doesnt happen with all models and I cant isolate a reason for it happening.
Any ideas???


#2

I has to be something in the way you’re constructing the model. (Or the creator if it’s something you didn’t create). Check for non-manifold edge (Mesh menu in Edit Mode, select non-manifold edges, and see if anything is selected. If so, that’s where your problem likely is.


#3

More precisely, go into edit mode, go into vertex-select sub-mode, make sure no vertices are selected (press A until nothing is selected) then select non-manifold from Select > Non-Manifold.

You can also select > non-manifold from edge-select mode which may or may not be useful for working out what exactly is causing the break. It won’t work from face-select mode (the menu option won’t even be there).

Some things that often trip me up by making things non-manifold:

  • accidentally having a distant vertex selected when I merge verticies.
  • accidentally having a distant vertex or edge selected when I create a face.
  • accidentally (or deliberately) deleting a vertex, edge or face and forgetting to fill the gap left behind (often when optimising a mesh by hand I can create a bit of a mess of missing bits which take multiple attempts to fix up!).

#4

Excellent answers, thanks @John_Laury for the lead and @glenalec for the fine detail, selecting non-manifold showed lots of faces and vertices selected.
So I just unselected them, havent tried to upload yet but I am very grateful for what seems like a solution.

And yes this happens with objects I am trying to convert from other sources. Only happened once with a test cube when I used the default blender cube (realizing why everyone suggests deleting this before starting, even if you want a cube.)

Thanks again, I will report my results.


#5

Not sure what you mean by “just unselected them” there. You need to have the mesh in a state where select-non-manifold ends up not selecting anything. To achieve this you will need to fill in missing faces and possibly remove verticies/edges/faces that are in the wrong place (such as creating impossible surfaces).

More Tips (as I remember them):

  • Select all and Mesh > Normals > Recalculate Outside (or Recalculate Inside) can also fix up Non-manifold issues where the face is correct but the normals have ended up on the wrong side.

  • Non manifold edges/verticies on edges of 2D shapes aren’t generally a problem (for example my lake surface is presently a 2D disk so its edges are non-manifold as they don’t connect to anything).

  • Select Loose Geometry and Select Interior Faces are also useful in tracking down where the breaks are. Their output will vary depending on which selection sub-mode you are in (vertex, edge or face).


#6

@glenalec by “just unselected them” I was thinking from what John said…
"select non-manifold edges, and see if anything is selected. If so, that’s where your problem likely is."
That they need to be not selected, but deselecting them doesnt remove the non-manifold issues, now I understand it just displays them. Thanks for the extra information, as soon as you mentioned 2d shapes a penny dropped.
My problem was the mesh was a plane, folded as an interior scene designed to only be seen from the inside, and exported from Unity3D. Blender wasnt happy.
I found the solution, Solidify all plane mesh objects, then recalculate outside, some needed to be fixed manually but the result was an acceptable inside and outside.


#7

Solidify can add alot of extra geometry. Many times, you’ll have two verts in the same place, if you were to grab one and move it and it creates a “hole” in the mesh, that’s the issue. You can often solve it by selecting both verts and merging them into one which “welds” the two faces together. Glad I was helpful, and thanks @glenalec for getting more specific!