Minecraftforge: [1.13] Specific y-levels in water behaves like you're in air.

[SilverDavidMC]

When being in water with a y-level of x.37847 or similar where your eye level is above the surface of water, the game treats it like you're in air. Instead of water behaving as a full block when water is above it, it always behaves as a surface source block. The behavior is similar to the screenshot shown, but pretend the end portal frames are water sources with air gaps.

[williewillus]

could you check if the problem happens in vanilla?

[SilverDavidMC]

Already tested. This same bug occurs in one of the 1.13 snapshots, but not the full release.

[LexManos]

Alright, this is a stupid one. This DOES happen in vanilla just very rarely.
Vanilla uses the formula: eyes < (double)(pos.getY() + state.getHeight() + 0.11111111F);
Forge uses the formula: eyes < (double)(pos.getY() + state.getHeight() + 0.1F);
Spot the difference.

getHeight() is level / 9.0f which is odd considering the max a fluid can be is 8, so 8/9 = 0.88888888F
Which is why they add the stupid number 0.11111111F, turns that into 0.99999999F. And considering vanilla uses double for positions, TECHNICALLY this can occure for 0.99999999F < Y < 1.0D

Forge's side just expands the issue because I used 0.1F, instead of 0.11111111F.

[Barteks2x]

Actually, 8.0F/9.0F + 0.11111111F == 1.0, so this is not an issue in vanilla at all. More specifically, there is no 0.99999999F. When you try to get such float, you get 1.0F

[LexManos]

That is not held out in the actual code. As I stepped through it and verified it myself before posting/pushing the fix. Unless my IDE suddenly decided to start lying to me about the value of variables. But thanks anyways.