Dried ghast's model is very unoptimized, causing rendering lag and other problems

Relates to: MC-260296 MC-262427 MC-262452 MC-262461 MC-262470 MC-262527 MC-262641 MC-262652 MC-262689 MC-262953 MC-267127 MC-267281 MC-267315 MC-267864 MC-279350 MC-279354 MC-279617

The bug

Dried ghasts have a model that is defined rather wastefully. A total of 42 quads are used for defining the geometry (icluding 6 that are never visible normally - see MC-296951), as well as six texture files per hydration state (one of which is 32×32 - see MC-296819). If we’re more intelligent about how we define the faces, we can obtain an outwardly visually identical result using only 28 faces instead of 42, which improves performance by a lot in areas with many dried ghasts. The texture mapping is also more visually obvious, using only five 16×16 texture files instead of six (and also eliminates a bunch of unused pixels - see MC-297324).

How to reproduce

A resource pack that reworks the models and textures used by dried ghasts is attached to this ticket.

To demonstrate the improved performance:

1. Set your render distance to 12, and optionally also disable VSync

2. Create this superflat world: 20*minecraft:dried_ghast;minecraft:the_void

3. Enter Spectator mode, then use F3+2 to show performance graphs

4. /tp @s 0 0 0 0 90

5. Observe the performance with and without this resource pack

Expected results

Good performance in vanilla.

Actual results

We can do so much better, as the resource pack proves.

How to fix

It should be possible to rip out vanilla’s current textures and models for dried ghasts and replace them with these - the outcome looks identical but the performance isn’t awful. Mojang have my full permission (and very strong encouragement) to use the game assets included in the resource pack as they see fit to resolve this issue.