Stealth design notes

These notes cover the stealth system in code, building on the overview on the main page.

The stealth math

The per-piece reduction is a multiplier of one eighth, applied to the visibility value the targeting system uses, so a full suit multiplies by one half. That is why the reduction is proportional across mobs. A standard hostile mob with a 16-block follow range is cut to 8 blocks, a zombie family mob at 35 to 17.5, a Blaze at 48 to 24, an Enderman at 64 to 32, and a Ghast at 100 to 50. The percentage is the constant, and the starting range only changes the numbers.

How the crouch works

Two mixins make the crouch. The first hooks TargetingConditions, the object mobs use to pick targets, and makes its test method return false when the wearer has the full suit and is crouching, so mobs never acquire you in the first place. The second hooks Mob.asValidTarget, the shared path for both getTarget and setTarget, and rejects the stealthed wearer there, which clears an existing chase the moment you crouch and stops it being re-acquired. That is why a mob mid-chase drops you instantly instead of resuming.

Why other players still see you

The crouch applies the game's Invisibility effect, in code MobEffects.INVISIBILITY, but the rendering is changed so the wearer shows as a translucent ghost rather than vanishing, the way spectators appear. The effect is granted for 200 ticks, which is ten seconds, and it is refreshed while you stay crouched, so it never lapses mid-hide. It is removed the moment you stop.

A singleplayer quirk

Removing the effect needs a per-instance flag because of how singleplayer runs. The client and the integrated server tick separate instances of the same player in one JVM, so a shared set of players to clean up after would break, since whichever side ticks first would consume the entry and leave the other side's local effect stuck. The per-instance flag also means the mod only ever removes the invisibility it applied, never one from a potion.

What it taught me

Making the mod taught me how to make a mod in Fabric. It was also the first project where I used proper version tags in the CI pipeline, with the release workflow bumping the patch version and cutting a tagged release on every push to main. I plan to carry that habit into future projects, and it started me thinking more about Git commit etiquette.