Create Optimized Trains

Performance optimization addon for Create Mod trains (Forge 1.20.1).

=============================================

ATTENTION: THIS MOD IS STILL IN BETA! PLEASE BACK UP YOUR MAP BEFORE USING THE MOD!

=============================================

Features

1. LOD (Level of Detail) for Trains

FULL — Real carriages with full physics (player nearby)
MEDIUM — Simplified physics, normal rendering
LOW — No physics, no collisions, minimal contraption updates
GHOST — Ghost entity, no rendering, abstract data only

2. Carriage Grouping / Abstraction

Merges multiple carriages into a single logical entity (TrainGroup)
Stores only: length, speed, position, carriage list as NBT
Expands back when the player approaches

3. Safe Multi-threading

Secondary thread (safe):

Route calculation
Collision prediction
Schedule optimization
Priority management
LOD decisions
Predictive simulation

Main thread (required):

Actual entity movement
Create physics
Rendering
Block interaction

4. Tick Throttling (Partial Updates)

FULL: every tick
MEDIUM: every 3 ticks (configurable)
LOW: every 8 ticks
GHOST: every 20 ticks

5. Render Optimization

Disables animations for distant trains
Skips full rendering for GHOST LOD
Reduces particles and visual effects
Hides internal details when not visible

6. Proxy Entities

Lightweight entity representing the entire train
Replaces dozens of contraptions
Keeps position, speed and direction
Recreates real carriages when needed

7. Smart Chunk Loading Management

Loads only essential chunks
Unloads chunks behind the train earlier
Pre-loads chunks ahead
Anti-thrashing (prevents repeated load/unload cycles)

8. Physics Optimization

Simplified physics for distant carriages
Disables collisions between carriages at low LOD
Reduces bogie checks
Disables internal contraption physics when far away

9. Networking Optimization

Sends updates only when speed/direction changes
Batches packets (delta compression)
Reduces sync frequency for distant trains

10. Priority System

Priority by type (EXPRESS > PASSENGER > FREIGHT > LOW)
Conflict resolution at junctions
Track segment reservation
Async conflict analysis

11. Dynamic Performance Monitor

NORMAL (TPS >= 18): full fidelity
DEGRADED (15 <= TPS < 18): light optimizations
CRITICAL (TPS < 15): aggressive optimizations, reduced LOD distances

Configuration

File: create_optimized_trains-common.toml

All features are individually configurable with distances, intervals and toggles.

Backported Fixes from Create 6.0.9+

Create 6.0.9 (for Minecraft 1.21.1) introduced several important fixes that were never backported to 1.20.1. Since 1.20.1 is no longer receiving updates from the Create team, this mod backports the following fixes for users staying on 1.20.1:

Contraption Collision Box GC Pressure (#6902)

Original problem: When train doors open/close at a station, gatherBBsOffThread() combines ALL block collision shapes into a single VoxelShape using Shapes.joinUnoptimized() — an O(n²) operation that creates massive temporary objects. The garbage collector can't keep up, causing lag spikes of 1-30+ seconds depending on train complexity.

Our fix: ContraptionCollisionMixin replaces the collision gathering algorithm with the same O(n) approach used in Create 6.0.9 (commit 8f30c2c). Instead of joining VoxelShapes, it collects AABBs directly from each block's collision shape — no intermediate allocations, no GC pressure. Also includes related duplicates: #4607, #5685, #9026, #9389.

Train Stutter from carriageWaitingForChunks

Original problem: In Train.tick(), when a carriage enters an unloaded chunk, Create sets carriageWaitingForChunks which forces speed = 0 until the chunk finishes loading. On maps with many trains and limited view distance, this causes 0.5-1.5 second freezes every time a train crosses a chunk boundary.

Our fix: TrainMixin redirects all reads of carriageWaitingForChunks in tick() to always return -1, so speed is never zeroed. Combined with the Smart Chunk Loading system (pre-loading chunks ahead of the train), trains move continuously without stutter.

Collision Check Performance

Original problem: collideWithOtherTrains() runs every tick for every train, which becomes expensive on maps with 20+ trains.

Our fix: TrainMixin throttles collision checks adaptively based on server performance — every 4 ticks normally, every 8 when degraded, every 12 when critical. Each train's check is offset by its UUID hash to distribute the load evenly across ticks.

Dependencies

Minecraft 1.20.1
Forge 47.1.33+
Create Mod 6.0.8+
Flywheel 1.0.6+ (bundled with Create)