[MC-81654] Water and lava top texture does not get rendered in some cases

The bug

It seems that the top of water doesn't get rendered if there is transparent block (this also includes slabs for example) in a 1 block radius one block higher than the water. This makes water look pretty strange if it is tilted.

How to reproduce (general steps)

Fill a 3 x 4 area of a solid block like stone
Place water or lava below middle block at the edge of a 3 blocks side
Move inside the lava or water block and rotate in the direction of the area you filled

How to reproduce (commands)

Use the following commands without moving

Optional to make sure the water or lava block does not move you
```
/gamemode spectator
```
```
/tp ~ ~ ~ 0 0
```
```
/fill ~-1 ~2 ~ ~1 ~2 ~3 stone
```
```
/setblock ~ ~1 ~ water
```

Attachments

MC-81654.mp4

Water top texture missing no transparent block (1.8.7).png

Water top texture transparent block (1.8.7).png

Comments 14

bemoty 2017-08-18T01:15:41Z

Can confirm for MC 1.12.1.

bemoty 2019-11-10T16:41:07Z

Confirmed for 1.14.4.

wobst.michael 2020-06-10T23:08:59Z

Can this still be reproduced in 1.16-pre3?

j_p_smith 2020-06-14T18:37:24Z

Confirmed in 1.15.2, as well in 1.16 Pre-release 5 with graphics set to "Fabulous!"

Avoma 2021-01-15T14:22:57Z

Can confirm in 20w51a. Here's the updated 4th reproduction steps as flowing_water no longer exists in the latest version.

/setblock ~ ~1 ~ water

4 more comments

Avoma 2021-03-27T15:03:51Z

Can confirm in 21w11a.

Avoma 2021-04-17T14:25:43Z

Can confirm in 21w15a.

Avoma 2022-05-10T17:21:35Z

Can confirm in 1.18.2 and 22w18a.

Avoma 2022-10-24T13:56:38Z

Can confirm in 1.19.2 and 22w42a.

douira 2024-11-04T20:00:53Z

I've conduced a test, and removing the `FluidState.shouldRenderBackwardUpFace` check makes this issue go away, however it also substantially changes how flooded caves look from the inside and generates twice as much geometry for their water surfaces. To both make sure inside upper water faces are generated for flowing water and flooded caves don't regress, a better heuristic for distinguishing these cases is needed, i.e. this bug is kinda complicated.

I've attached a comparison image.

[media]