Blacked out geometry


(Alexanderesmith) #1

Some of my geometry is black instead of the color I set to it, and I'm not sure how it happened.

Surface test 2015-02-01 by AlexanderESmith on Sketchfab

Ironically enough, I'm seeing this behavior on a Surface Pro 3 (i5), in Firefox and IE. I checked to make sure the object didn't have an odd material, the normals are all pointed in the right direction, and the object's settings are as correct as I can make them in the Sketchfab settings.

Any thoughts? Can anyone confirm that this is happening? The geometry in question is the top half of the back of the surface itself.

Cheers,

Alexander E. Smith
AlexanderESmith.com


(Andy lewis) #2

Yup. I can see it in Safari, I've had the same thing happen with a couple of files recently. Afraid I can't share a link as its a private file but I'm certainly finding I'm getting some deep black, non-reflective faces.

Cheers!

AndyL


(Stephomi) #3

@alexanderesmith We are on it :).

The normals are indeed in the right direction.... but some triangles are not pointing in the right direction (clockwise order).
For us, it's important to have the normal pointing in the same "direction" of the triangle, as we can flip the normal if we are on the opposite side of the triangle (for double rendering).

I remember that we already had this problem with one of your other models. Did you use the "flip normal" option in blender (I think it flips both the triangle and the normals, not sure about it), or something else?


(Alexanderesmith) #4

Hm.

Well, I'm uploading as quads, not tris, so I don't exactly know how that could have happened. Flipping the normals was the first thing I tried.

I'm not quite getting what you're saying, it almost sounds like your saying the faces are not flipped, but rotated?

Yes, we had this issue on one of my gameboy renders. Never figured that one out, actually :/

Thanks,

Alexander E. Smith


(Stephomi) #5

example here with half of the sphere inverted (with back face culling)

Sphereflip by stephomi on Sketchfab


^ the normals are always in the same direction as the faces (tris or quads...), so it work "fine"
(back face culling is independant of normals, it just uses the face clock wise order).

The black faces issue occurs when the normals on the vertices are pointing to the opposite sides of the surrounding faces.
I tried to find the source of the problem on one of the black face on your .blend, but I couldn't pinpoint it.
(There's a mirror and a subdiv modifier but the base geometry was suspect (like overlapping faces, edges and vertex)).


#6

I've seen an issue where the mirror modifier messes with lit faces.