Cycles bug, Rhino bug, or?

See exhibit A:

Much of the shape is in light, part is in shadow.

If you look at the line (region) between the region of light and the shadow you can see something odd.

Some facets are smooth shaded and some are not.

Exhibit B shows the render mesh:

The edges of the flat facets seem to lie along the edges of thin quads (tall/thin or wide/short) in the render mesh but there are many thin quads that don’t seem to be flat shaded.

I have instances of this problem all over my model. I am uploading the 3dm file but be warned that it’s big. It’s about 295 Mb.

Smooth shading facets was solved back in the teapot age of computer graphics. As I understand it: you take the vertex normals and interpolate between them. So I wonder of Rhino is, I dunno, creating parallel vertex normals or if there is a bug in cycles and it can’t draw teapots properly because, now that I think of it, my shape is very tea-potty and it’s not drawing properly. :slight_smile:

1 Like

I have good news and bad news.

The good news: the default Rhino renderer and IRay don’t have dubious flat facets so it’s most likely to be a Cycles problem. This is good news for you McNeel guys.

The bad news, and it’s really bad news for me, is that I now have to deal with Blender tech support. I’m depressed, I’ve had bad interactions with them, I think I will just use IRay. :wink:

McNeel guys, I’m straw-clutching here, is there any possibility that the problem is on your end?

Boy I’m depressed. I think I will do some modelling now to cheer myself up.

Have you tried changing the render mesh settings using Tools > Options > Mesh then use “Smooth and slower”, or custom settings? It may be that the normals are indeed not correctly generated and using different settings will correct this.
Otherwise, extract the render mesh, hide the original object, then run RebuildMeshNormals on the render mesh, see if that helps.

Hi menno, I tend to have the Smooth and slower option on. I tried a custom mesh with minimum initial grid quads set to 5000. This makes the quads smaller, the problem is still there but it’s harder to see, things look smoother from a distance.

I tried RebuildMeshNormals and things got worse. Note the stark dividing line at the front of the shape. This is also seen in the default Rhino renderer.

Exhibit C:

I suppose that I need to import the model, and the HDRI image used to light it, into Blender and see if the problem is there.

I’m going to download the latest Blender and try this. let’s see if the problem persists in Blender.