InputBooster 3.1.6-alpha — Minecraft 1.21.1 / 1.21.4 / 1.21.11

Alpha build. Client-side only; install it in mods/ alongside Fabric API.

Supported Minecraft versions

Each jar declares its own exact Minecraft range, requires Java 21, Fabric loader 0.19+, and Fabric API at or above the release it was compiled against.

Verified bug fixes

The same input-pipeline fixes as the modern line, ported to the 1.21.x sources:

• Native input sampling left the game thread. The poller no longer calls the platform key-state API; the game thread publishes an immutable snapshot once per rendered frame and once per tick, and the poller reads that. Sampling failures are reported once and degrade to tick-rate sampling.
• Shared key bindings. A key bound to two actions now dispatches both from the event path, matching the polling path (bit-mask resolution instead of first-match).
• POLL mode state tracking. Slots are updated in POLL mode (dispatch suppressed), so a mode switch never starts from stale state.
• Defensive copies for the key-binding arrays, so no caller can rebind an action by mutating internal state.
• Atomic click/scroll windows, so two threads cannot both accept a click in the same debounce window.

Legacy-specific notes

• Compiled and tested on a Java 21 toolchain; the jars declare a Java 21 floor. An earlier 3.1.5 jar declared >=25 and was rejected by the loader on 1.21.x.
• The 1.21.x Sodium releases used here do not ship the Config API, so these jars declare no Sodium entrypoint and always show InputBooster's own options button.

Custom keyboard handler and key mapping

Handler mode selection was not deterministic

The poller skipped the tick snapshot whenever the alpha custom handler was enabled, and nothing checked whether that handler could actually see events. On a client where the keyboard/mouse mixins did not apply this left the mod with no input source at all, silently. Source selection is now one pure decision (InputPollingThread.chooseSource, with a RAW/SNAPSHOT/IDLE result):

• native sampler usable -> raw, frame-rate sampled state;
• otherwise, custom handler disabled -> tick snapshot;
• otherwise, custom handler enabled and its hooks have delivered an event -> the handler owns input;
• otherwise (enabled but no event ever seen) -> tick snapshot plus one warning line, instead of dead input.

The active source is logged whenever it changes, a source switch resets the engine so no key is inherited as held, and the overlay's keyboard line now distinguishes "custom (alpha, live)" from "custom (alpha, no events yet)".

The player's real binding is respected, and fallbacks are named

Slot resolution still falls back to the vanilla default when a mapping cannot be read, but it no longer does so invisibly: KeyBindingSet records which slots fell back and whether the cause was a missing mapping or a failed accessor, and the fallback warning lists the affected slot names once. A mapping that resolves always keeps the key the player actually bound, including custom mouse buttons.

Registration happens exactly once

Fabric does not detect duplicate key mappings: registering the same KeyMapping twice adds a second row to the Controls screen and the player's rebind then applies to only one of them. The entrypoint now claims the single registration pass before registering, and createKeyMappings() still runs during mod construction, before registration and before any input path is wired.

Tests

The full suite (102 tests) runs on every target, including StabilityAuditTest (shared bindings, reset, aliasing, concurrent click claim, concurrent state updates, polling rates 60–1000 Hz, unavailable native state) and MixinTargetSignatureTest, which verifies every mixin hook against the resolved Minecraft jar for that exact version.