parametric with clipped_by or in intersection has holes

[LeForgeron]

A parametric get truncated to its first intersection when used with clipped_by or inside an intersection. Other intersections seems to be dismissed.

Illustration with clipped_by

Illustration with intersection

Scenes to reproduce (beware, parametric is slow, even for that small sphere) param.tar.gz

This behaviour has been verified also on the head of master branch :white_check_mark:

[LeForgeron]

isosurface has the same kind of issue, unless "all_intersections" is added. That would be a suitable behaviour. But all_intersections is not allowed so far for parametric

[c-lipka]

We need to decide whether to address this...

• by just documenting it as intended behavior (if it isn't documented already),
• by adding an all_intersections-like mechanism to parametrics, or
• by some other clever solution.

[wfpokorny]

I vote for documenting the one intersection returned behaviour in the near term no matter. It's not now as far as I can see.

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Related: The intersection behaviour sometimes causes shadow artifacts too - though, I cannot recall particulars at the moment. It was something like code somewhere filtering the one and only first intersection and because here we have a surface no effective shadowing gets done due the normal direction as happens with shapes in similar situations. But, too long ago...

Aside: There are too in self crossing surfaces, places where having a shadow_tolerance keyword is useful.