Just as I thought my model was almost finished, I noticed a couple of weird shadows.

I attached a kind of minimal example.

As you can see, almost everything about these books is straight, but the shadow is curved.
The lighting (which should not matter, I believe) is a “distant” directional light.

Does anyone know what can cause this kind of weird behaviour?

Kind regards,
Tempestas Ludi

Hi tempestas, it would be a lot easier to diagnose with a hip file.

That's pretty cool, how'd you do that?

While waiting for my post to be accepted by a moderator, I narrowed it down to a sort of minimal example.

The problem seems to lie in joining two non-parallel-or-perpendicular lines and then extruding them. This is also what I did in the first example with the books.

Is it possible that this is because of interpolation of normals? I would expect not, since shadows should be cast regardless of normals, but who knows…

I used the join operation in the books example because I wanted to have a shape that consisted of a couple of straight parts and a couple of curves. Is there a better way to do this? Or is this the best way?

Kind regards,
Tempestas Ludi

Ps. Does anyone know what causes the upper edges in my minimal example to display like thin, flat, polygons? I struggled quite a bit with those in a couple of previous projects.

it is your normals and vm_smoothP property that uses them to interpret P as smoothed for shadow casting to resolve some artifacts

you can get rid of it if you either make your model not rely that much on interpolated normals, especially if the surface should be flat
or add vm_smoothP (named Fix Shadow Terminator) render property to your object and turn it off

Thanks! That works splendidly.

Could you maybe also shed some light on the flaps that appear on the upper edges?

Tempestas Ludi

tempestas
Could you maybe also shed some light on the flaps that appear on the upper edges?

those are isolated curves shaded as ribbons
as your Extrude SOP has Front Face and Back Face set to Output
therefore you will end up with your curves duplicated at the base, then extruded Side Faces, then again duplicated curves at the end

so just set Front Face and Back Face to No Output

Ah, right. Thanks!