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EEVEE shadow from sun on incorrect face
Confirmed, HighPublicBUG

Description

System Information
Operating system: Windows 10
Graphics card: gtx 1070

Blender Version
Broken: 2.81,eba4a4bd73ba
Worked: (optional)

Short description of error

Exact steps for others to reproduce the error
Make a plane, extrude edge downwards put sun next to it and above the plane pointing towards the edge. The new plane that was extruded from edge will cast shadow on plane above it which makes absolutely no sense and is very difficult/impossible to fix/mask with trickery so I am reporting it as a bug. Here is the blend file for example:

Event Timeline

Philipp Oeser (lichtwerk) lowered the priority of this task from 90 to 80.Nov 19 2019, 11:52 AM

Would assume this is not a bug, but some limitation of cascaded shadow maps?

https://docs.blender.org/manual/en/dev/render/eevee/lighting.html#cascaded-shadow-map

Tweaking the settings [lowering suns max distance for example, playing with distribution, ..., also eevee shadow Cascade Size to maximum 4096px] helps making the artefacts less apparent.
(not seeing the Bias really having any effect here, so I am a bit on shaky ground as well)

Not being 100% sure, I will let @Clément Foucault (fclem) decide...
(I think what would be good is document the known limitations/artefacts with example images in the manual, so we can come back to these if neccessary...)

Clément Foucault (fclem) lowered the priority of this task from 80 to High.Nov 19 2019, 2:27 PM

The artifact is caused by shadowmap aliasing (low res). This is the only case where you want to increase the shadow bias.

But the real bug here is that the bias is multiplied by a really small value. If you type a really high value the bias is visible. I don't know if this is to be considered something critical to be changed prior release.

The bias is also dependent on the scale of the scene so I think there is some improvement to be made here.

I don't know if this is to be considered something critical to be changed prior release.

Tbh, I cannot judge how severe this is.
Maybe you should chat with @Nathan Letwory (jesterking) , @Dalai Felinto (dfelinto) ?