Content

Liquids

What a custom liquid is, and is not

Minecraft has two fluids and a server cannot add a third. A custom liquid is real water or lava, wearing your texture, with your rules applied to whoever is in it. It genuinely behaves like a fluid because it is one — you swim in it, boats float, it flows, other plugins see water.

Two consequences, both worth knowing before you build around it: the texture is per-pack, so every water on the server is drawn from the same picture — what a liquid gets of its own is a colour; and what tells acid from ocean is a volume, not the blocks in it.

# liquids/acid.yml
acid:
  base: water            # water | lava
  color: "#3FBF4A"       # optional
  effect: POISON
  amplifier: 1
  damage: 1.0            # per second
  fireproof: false

There are two ways to make a pool: mark out water that is already there, or build the pond in the first place with a bucket. They make the same thing.

Marking out a pool#

/rp liquid corner              stand at one corner
/rp liquid fill mypack:acid    stand at the opposite one
/rp liquid clear               removes the pool you are standing in
/rp liquid list                every pool, per world

The two corners define a box, and everything inside it that is the right fluid gets the rules.

A bucket of it#

# items/acid_bucket.yml
acid_bucket:
  material: BUCKET
  liquid: mypack:acid

Right-click a block and it puts one source block down and makes that place count as the liquid. A block placed against a pool of the same liquid joins it rather than starting a second, so a pond built click by click carries one rule, not fifty — and two builders filling the same pond from opposite ends end up with one pool between them.

What goes down is a real source block, so it flows. Water that runs out of the box is ordinary water: the colour and the rules stop at the pool, and a builder who wants a still pond digs a basin the way they would for vanilla water.

Why a box and not the blocks#

A lake is thousands of blocks that change shape as it flows. A per-block record would be wrong within a second of somebody breaking a bank, and would need rewriting every time the water moved.

A box does not move. It is a few numbers per pool, it survives a restart, and the fluid inside it can do whatever fluids do.

The cost is that a pool is rectangular and your lake probably is not. Use several overlapping boxes; a player is in whichever they are inside.

Colour#

color: takes "#3FBF4A", 0x3FBF4A, 3FBF4A or one of the sixteen dye names — RED, LIGHT_BLUE, LIME. Quote the # form, or YAML reads the rest of the line as a comment and you get no colour and no complaint.

A colour needs a restart, and it is approximate

The game tints water by biome, which is the only knob it has for this. RP Engine writes one biome per tinted liquid into a datapack in your world folder (datapacks/rpengine_liquids) every time content loads, and biomes are registered when the server starts — so a colour you added this session does not exist until you restart. The pool works in the meantime; it is just the wrong colour.

Two more things follow from it being a biome. Biomes are stored per 4×4×4 cell, so a tinted pool has a rim of tinted water around it. And the client blends biome colours across several blocks, so a pool under about 8 blocks across never reaches its full colour — a player with biome blend turned up sees less of it again.

Why the colour looks muted

The tint is multiplied by the water texture, and vanilla's is a dark blue-grey — so even #2BE04A lands as a murky green rather than the colour you picked. That is the ceiling of the mechanism, not a setting: ItemsAdder tints the same texture the same way and stops in the same place.

A pack can ship a paler water_still through overrides/ and get vivid colours out of it. RP Engine will not do that for you, because it would make every ocean on the server pale to make one pond green — that is a decision about somebody's whole world, not about a liquid.

Clearing a pool paints it back to the biome that was there when the pool was made. That is one biome for the whole box, which is all a pool records: a pool straddling two biomes comes back as the first of them.

Doing more than an effect#

effect and damage are applied by the engine every second. Everything else a server means by acid — a title, a sound, a quest step — is a PlayerLiquidEvent, which fires when somebody goes into a pool and again when they come out rather than every second they stand there.

The rules#

Field	What it does
`base`	`water` or `lava`. What it actually is
`color`	What colour it is drawn, as hex or a dye name
`effect`	A potion effect applied while inside
`amplifier`	Its level, 1-based
`damage`	Per second, on top of anything lava already does
`fireproof`	Whether a lava-based liquid stops burning you