The bug
Some places produce illogical shadows:
1.Strange shadows are created when placing blocks in the middle of a U-shaped structure.
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2.The fence arm in this structure is unusually dark.
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3.When the block is on the east or south of the wall.
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4.Strange shadows at the end of the fluid. Fixed in 1.17-pre2
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Related issues
is duplicated by
relates to
Attachments
Comments

Removed some screenshots that cannot be reproduced in 18w03b.

Affects 20w28a, requesting ownership

Walls, fences, glass, slabs and stairs don't seem to be affected anymore, but solid blocks, cobwebs, transparent blocks (such as the beacon, leaves (depending on your graphics) and the honey block seem to be affected) and also the blocks that emit light are. (As of 1.16.1/20w28a)

In 20w29a

Please provide a description of the issue.
@unknown, this ticket is describing the odd smooth lighting behavior that produces shadows in illogical places. For example, in one of the screenshots attached to this report (MC-95515.png), you can see that shadows are produced right beside some light sources, and this doesn't make much sense, as a light source is present, therefore no shadow should be produced. I hope this helps clears any confusion. Also can confirm that this issue is present in 21w05b.
Can confirm in 21w06a.
Can confirm in 21w07a.
Can confirm in 21w11a.
Can confirm in 21w13a.

I can no longer reproduce any of this in 1.17-pre2 except for the water issue.
I suspect it might have something to do with ambient occlusion.