apparently this is a duplicate but it is still present in 1.14 even though the other is marked resolved
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enabling mipmapping creates a graphical issue where the outlines of blocks create a
What I expected to happen was...:
mipmapping would mipmap and not create this bug
What actually happened was...:
it created lines that look through the void
Steps to Reproduce:
1. set mipmapping to any value (all seem to have the same effect)
2. save settings
3. look for a place where the ground is >1 block lower than you and about 5 away and look for teal/orange lines depending on the in game time
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I have just started experiencing this bug. to replecate go on a super flat world with mipmap level 4 and you can see it really noticeable.

it might be caused by OpenGL 2.0
Thank you for your report!
We're actually already tracking this issue in MC-1794, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.