Blender Discussions

[nervagon]

I often use the face weighted normals modifier on relatively low res geo, and I’ve been experiencing weird black shading artifacts around the edges of meshes. I googled it, and it seems that this is a known limitation with prorender that C4D users also deal with. Here is an example of a C4D user experiencing the exact same render defects:

Cinema 4D Quick Tip: Remove Shading Artifacts in ProRender - YouTube 

The best way I can describe the problem is that prorender doesn't seem to calculate vertex normals correctly which leads to ugly black edges that almost look like a toon shader.

I've attached a very simple blender 2.8rc2 test scene. Platform is windows 10. The issue persists on 2 machines, both with nvidia gtx 1080 ti and latest studio drivers.

[gelert]

Thanks for posting this from Blender Artists. I've also experienced this kind of artefact but didn't know what was causing it. Hopefully the devs can offer some insight or a fix.

[plasmapeppers]

Doing some testing in Cinema showed that this only happens when a traditional light is present in the scene. HDRIs for some reason do not trigger this kind of behavior. Here are a few interesting things I noticed: 

Using very low geo objects triggers the most noticeable shading error: 

This isn't present on higher geo objects or if phong is disabled:

Beyond simple shading errors, it appears that this issue also affects reflections - presumably because the Fresnel angle  is beyond 90 degrees (which is also probably why it is black without reflections):

And of course this isn't the case with higher density geo or phong removed:

After some further testing it appears that this isn't an RPR limitation though, but rather a physical reality of how light works. The same phong shading issues are present with just the OpenGL viewport, Standard and Physical renderers, Blender's OpenGL viewport, EEVEE, Cycles. As the viewing angle increases beyond 90 degrees, the object shouldn't be visible anymore. Yet the light rays are still hitting it, so it returns in ways that are unexpected. For the gloss renders, at 90 degrees the total light reflected is 100% as it should be.

[nervagon]

To keep things fair, I have rendered the exact same mesh using only the sun/sky lighting in both prorender and octane using the pathtracing kernel. The results in octane are clean, and as expected. The results in prorender are still broken. So this cannot be dismissed as simply a limitation inherent to unbiased pathtracers. Attached.