black edges occur when zoom in about vk_raytrace

[droettger]

That is a usual artifact when rendering low-poly models with interpolated per-vertex shading normals.

At high geometry curvatures, which appear along the silhouettes of this object, it can happen that the interpolated shading normal across a triangle primitive actually doesn't lie inside the same hemisphere as the direction to the viewer (negative ray direction) and that's a false condition for the lighting test. For the shading calculation that's like looking at the backface of an opaque object. (This would not happen when using the face-normals instead of the shading normals, but then you get a facetted look.)

Similar effects would arise when the sampled continuation ray in a path tracer would continue below the geometric surface of opaque materials, which also happens regularly with bump- or normal-maps.

This site has some nice images explaining interpolated shading normals:
https://www.scratchapixel.com/lessons/3d-basic-rendering/introduction-to-shading/shading-normals

The black areas are running into the dot(V, N) < 0.0 case.

[Kuranes]

@f1shel FYI
it's know topic with possible mitigation stragegies
as per the publication "Consistent Normal Interpolation", Reshetov et al., 2010
https://blog.yiningkarlli.com/2015/01/consistent-normal-interpolation.html
and an implementation here

• https://github.com/jbikker/lighthouse2/blob/dcc64b4a401b7d0db4b3e75c1f3dbcfd8adb3102/lib/rendercore_vulkan_rt/shaders/tools.glsl#L259-L279
• https://github.com/jbikker/lighthouse2/blob/dcc64b4a401b7d0db4b3e75c1f3dbcfd8adb3102/lib/rendercore_vulkan_rt/shaders/tools.glsl#L259-L279

[f1shel]

another example