Magical gene / no coat effect

Weather sensitive (speed)

How the sky changes what the horse can do. A positive and a negative allele for each kind of weather, incompletely dominant, with the size of the effect written on each allele copy. Unlinked to the jump locus — a horse can love the rain and be no better at fences in it.

Built, and not yet seen in game

The gene, its inheritance and its founder table exist and are covered by the test suite; the translator that turns it into behaviour was written against the 26.1.2 sources and is flagged unverified in its own comments. Nothing on this page has been watched happening to a horse. What to look at, and what is most likely to be wrong, is on To be verified.

What it does

A positive allele and a negative one for each kind of weather. One copy moves moving speed by the percentage written on that copy while its weather holds; two copies add both percentages. One of each very nearly cancels.

Combination	Outcome
two positive copies	both percentages, added — a real difference
one positive copy	that copy’s percentage
one of each	near enough nothing
one negative copy	that copy’s percentage, off
two negative copies	both, off — noticeable and annoying

What it is like to own

Nothing at all, most of the time. Then it rains, and the horse you have ridden for a week is a different animal. It is the only locus in the mod whose expression you cannot check on demand — you wait for weather.

Health

None directly. A badly weather-sensitive horse is slower or shorter in the stride when it rains, which is a hazard only if you were relying on it.

Gene key: horsegenetics.weather_speed
Alleles: a positive and a negative per weather type, plus n
Inheritance: incomplete dominance — copies add
Reaches the game as: an attribute effect on movement_speed, gated on raining / thundering
Epigenetic: the magnitude, per allele copy
Coat effect: none, ever

Correction: this is not a copy of swim speed

An earlier draft of this page said the gene was “nearly a copy” of swim speed on AbstractMagicFactorGene. That base class is strictly three alleles — one that pushes the quantity up, one that pushes it down, and the wild type — so it cannot express a positive and a negative allele per weather type. What it genuinely provides is the inheritance: codominance, a percentage drawn per allele copy, and both copies adding with the down allele counting negative.

So what it actually needs

Two options, and they are a real choice rather than a detail:

One locus per weather type — rain speed, storm speed, and so on — each one a genuine AbstractMagicFactorGene subclass costing almost nothing. Cheapest by far, and it multiplies the locus count by the number of weathers, twice over once the jump twin is counted.
One locus, several signed pairs — alleles Rain+, Rain−, Thndr+, Thndr− and the wild type, each carrying its own epigenetic delta and its own condition. This needs a generalisation of the factor gene to several conditioned pairs, which is new code — but it keeps the locus count at two and gives a genuinely interesting compound heterozygote: a Rain+/Thndr− horse is better in rain and worse in storms, and both halves apply independently because their conditions never both hold.

The second is what this page describes and what the design settled on. It is not free, and the estimate should say so.

Snow is not weather in Minecraft

There is no snowfall state to test — snow is rain in a cold biome. A snowing flag is therefore a biome lookup, not a weather one, and belongs on an interval sample rather than in a per-tick condition check.

Removal is already handled

The attribute path reconciles every tick and clearAttributes takes off any modifier the horse is no longer asking for — which is the half that would otherwise leave a rain bonus stuck on a horse standing in sunshine. Nothing new to write.

The two weather loci are deliberately unlinked

Speed and jump are separate genes with separate founder tables and no shared state, for the same reason swim speed and water breathing are separate: crossing a river quickly and surviving the bottom of a lake are different problems, and a breeder who wants both should have to select for both.

The roadmap said the attribute verb was dead. It is not

§1.3 claimed the attribute effect “parses and is never applied”. That stopped being true when applyAttribute landed; the verb is wired, scoped per gene so two genes may move one attribute without fighting, and flagged unverified rather than absent. This gene and eyesight both depend on it.

A locus you cannot look at

Every other performance gene can be measured whenever you like. This one can only be measured when the weather agrees, which makes it the first locus in the mod where the gene database is genuinely easier than observation. That is the point of it: it gives the testing layer something to be better at than looking.

Weather sensitive (jump) Magic swim speed Eyesight locus What to check in-game

Planned source: common/genetics/genes/WeatherSpeedGene.java