Crate vectis_crdt 

vectis-crdt

CRDT engine for collaborative whiteboards.

vectis (lat.) = arrow, vector.

Architecture

See [ARCHITECTURE.md] at the crate root for a comprehensive technical description of every design decision, algorithm, and trade-off.

Quick overview

The whiteboard state is two independent CRDTs:

• rga::RgaArray — YATA-style Replicated Growable Array for z-order. Each item is a stroke (not a point), so n is in the hundreds, not millions.
• stroke::LwwRegister — Last-Write-Wins register per stroke property (color, width, opacity, transform). Independent registers enable granular concurrent merges without conflict.

The root entry point is document::Document. The Wasm-facing API lives in [wasm_bridge::WasmDocument] (feature wasm).

Feature flags

Feature	Default	Description
wasm	yes	Enables wasm-bindgen and the JS API
compress	no	Enables LZ4 compression for updates > 200 B

Module map

Module	Role
types	ActorId, LamportTs, OpId, VectorClock
rga	YATA-style RGA, RgaArray, RgaItem, ItemState
stroke	StrokePoint, StrokeData, Aabb, LwwRegister, StrokeProperties
document	Document root, all CRDT operations, LwwMap
gc	Incremental tombstone GC with MVV gating and origin re-parenting
encoding	Binary wire format: LEB128 varints + LE floats
causal_buffer	Buffers out-of-order remote ops until causally deliverable
awareness	Ephemeral cursor positions (TTL-based, not CRDT)
compression	LZ4 feature-gated threshold compression
error	VectisError, VectisResult
[wasm_bridge]	WasmDocument: zero-copy JS API (feature wasm)

Modules

awareness

Ephemeral awareness state — cursor positions and actor presence.

causal_buffer

Causal ordering buffer.

compression

LZ4 compression layer for the wire format.

document

encoding

Binary encoding/decoding for operations and state.

error

gc

rga

stroke

types