Extruded curve renders incorrectly (Bug? Or am I forgetting something?)

Hi all
I made a simple spiral, created a bevel and taper, and when rendering there is a very strange shadow artifact: the ribbon immediately falls under shadow.



If I convert it to a mesh (alt+C) the artifact disappears (this isn’t about my lighting, i.e.). Blend attached – is there something I’m doing or not doing with the curve here? Thanks for any help!

Also, if you think this is a bug, let me know and I’ll submit it.

Attachments

weirdShadingOnCurveExtrusion.blend (492 KB)

yes I get the same weird clip and notice an odd shadow at the back too. I added a thickness modifier and it went away, I also tried it in 2.49b and it rendered ok but deformed a bit.

Perhaps this is a shader or material error?

Hey this is weird! I just added the modifier (thickness) and turned it off (poked eye shut) and it rendered fine! Don’t use a zero value though as it gets really strange. There might be a bug report in this.

Rendering it from the top makes it seem as though there is a render space issue, possibly resolved when the nodifier is applied (even if off).

What’s the “nodifier”?

Ah – Modifier. Sorry for missing that. Brilliant discovery, David. I think I’ll submit this as a bug, but I’m glad to have a painless workaround for now (apply a solidify modifier, turn it off if you don’t need it but leave it there to fix the bug).

Wait: the disabling trick doesn’t actually work. You probably only disabled it for the viewer, but not for the render. Disable it for the render and you’ll see it comes back.

Oh dear, sorry. Just give it a really small value then.

PS sorry for nispelling, it nust be ny keyboard

Update: I submitted the bug, Cambell confirmed it and fixed it. From the first post here to the fix and new revision of blender, in less than a day. Simply amazing!

Wow thats anazing!