Minecraft generates mipmapped textures for signs, but does not use them

Relates to: MC-276568 MC-277447 MC-277450 MC-277470

The bug

When loading the game's resources, Minecraft generates mipmapped textures for all types of sign. However, it does not use them at all, wasting game resources.

How to reproduce

A resource pack is attached to this ticket.

1. Download and apply the attached resource pack

2. /fill ~ ~ ~ ~5 ~60 ~60 oak_sign[rotation=12]

3. /fill ~ ~ ~ ~5 ~60 ~60 oak_planks

4. Compare

Expected results

The signs would fade into a smooth gray in the distance, much like the planks.

Actual results

No such thing happens and we get incredibly grainy Moire patterns.

How to fix

Either make signs use mipmapping like other blocks (easily doable if they get converted over to use proper block models), or don't generate these mipmapped textures for signs at all. Several other atlases (gui, map decorations, mob effects, paintings, particles) don't generate mipmapped versions of themselves, so why should signs if they're not going to be used?