Three.js: mesh both receive and cast shadow seems odd

[leoboboyan]

Description of the problem

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Three.js version

• [ ] Dev
• [x] r91
• [ ] ...

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Hardware Requirements (graphics card, VR Device, ...)

Here is an example, export from threejs.org/editor

scene.json.zip

thanks!

[donmccurdy]

This shadow doesn't look unreasonable to me, what part seems odd?

[leoboboyan]

there are so many dark streaks on the object.

when set receive shadow to false, it's gone. @donmccurdy

[Usnul]

In short:

• shadow acne (https://computergraphics.stackexchange.com/questions/2192/cause-of-shadow-acne)

Problems:

• shadow mapping algorithm is rather simple, more complex algorithms address this issue to some degree
• shadowmap resolution is too low in the acne region. This can be addressed by increading resolution or tightening the shadow camera frustum
• normals on the cylinder are not "smooth", this causes each face to be shaded as an individual surface, resulting in unpleasant artifacts when combined with shadow acne.

I suggest you research a bit into shadowmapping - it will help you understand problems like this in the future and how to deal with them better.
You might find a discussion here useful: https://github.com/mrdoob/three.js/issues/5554

[leoboboyan]

thanks a lot! @Usnul

[WestLangley]

Those are artifacts caused by self-shadowing, and the question has been answered on stackoverflow.