black edges occur when zoom in

[f1shel]

Hi, thanks for this greate project!

I encountered a problem which seems like a bug.

Take the robot-toon scene for example, when you zoom in to observe the model, some black lines will occur around the contour, as shown in the figure below.

This will also happen to other contours. Is that a bug?

[f1shel]

another example

[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