Changelog: Celeris v0.2.0 (1.21 – 26.3)

Celeris gains a batch physics engine: other mods hand it thousands of entity bodies, and it simulates them off-heap, in parallel, on a native SIMD kernel, following vanilla's own movement rules. Like the rest of Celeris it adds no gameplay by itself; Velox is the first mod built on it.

Key Features & Changes

• Batch Physics Engine: Bodies live in one cache-aligned, off-heap Structure-of-Arrays batch; gravity, terrain collision and drag run fused per 1024-body chunk across worker threads.
• Native Kernel: C++ with AVX2/FMA, AVX-512 and NEON variants chosen from the CPU at startup, bundled for Windows, Linux and macOS.
• No Flags Required: Without FFM (Minecraft 1.21.x without --enable-preview) or without a native library for the platform, the same engine runs on a pure-Java kernel over Java arrays, with the same results. The JVM flags only make it faster.
• Vanilla Rules: Item movement follows Minecraft 1.21.1's Entity.move on plain terrain, and the native and Java kernels agree bit for bit; anything the engine does not model (fluids, partial blocks, special blocks) is handed back to vanilla for that tick.
• Entity Broadphase: Finds overlapping bodies (merge or push candidates) in one O(n) pass.
• Entity Bridge: Keeps entities and their simulated bodies in sync without per-tick allocation.

Performance

• About 30 ns per body per tick on one core with the native kernel, and about 10 ns with 4 cores (50 000 items).
• The pure-Java kernel needs no flags and is roughly 1.5x slower than the native one. For the native kernel on Minecraft 1.21.x add --enable-preview --enable-native-access=ALL-UNNAMED; on 26.x it is used without flags.