ChunkTest

This repository contains an idea how to implement chunks using the Unity Job and ECS tech stack.

Idea

The system handles a fixed number of chunks in memory and loads/unloads before or after gameplay simulation as needed. Like with entities removing a chunk during simulation is not allowed. There is an example LivenessManager which performs those actions in the project.

The Map holds a primary NativeArray<ChunkData> of chunk information and as many secondary NativeArray<T> as needed to store per-tile data. A Tile is very much like an Entity and per-tile data are very much like components.

The ChunkData contains an index into the per-tile arrays pointing to the first tile that belongs to the chunk, the following CHUNK_WIDTH * CHUNK_HEIGHT tiles also belong to that chunk. ChunkData also has an index to the chunks to the left, top, right and bottom of it in the NativeArray<ChunkData> (or -1 if there is no chunk). This effectively forms a 2D linked list where a System can perform lookups into the 4 cardinal directions by chasing the indices in ChunkData. At worst a system should have to look into the data of 4 different chunks, if the entity is positioned near a corner.

An Entity should always have an updated index on which chunk it is before dispatching ECS systems, so that jobs can use that index as a starting point for queries into the tile data. If the entity chunk index is set as a SharedComponentData, the ECS should group entities with the same value next to each other, so that chunks remain hot in memory source.

Code Outline

public class Map
{
    // Chunk Information
    public NativeArray<ChunkData> Chunks;

    // Per-tile collision data
    public NativeArray<CollisionData> CollisionData;

    // Per-tile custom data
    public NativeArray<MyOtherTileData> OtherTileData;
}

public struct ChunkData
{
    // Index into per-tile data arrays
    public int TileIndex;

    // Index into chunk to the left in ChunkData
    public int Left;

    // Index into chunk to the top in ChunkData
    public int Top;

    // Index into chunk to the right in ChunkData
    public int Right;

    // Index into chunk to the bottom in ChunkData
    public int Bottom;
}

public struct CollisionData
{
    /*
     * Bits:
     * 0 - Collides Left
     * 1 - Collides Top
     * 2 - Collides Right
     * 3 - Collides Bottom
     */
    public byte CollisionMask;
}

public struct MyOtherTileData
{
    public float MyOtherTileValue;
}

Resources

• RustConf 2018 - Closing Keynote - Using Rust For Game Development by Catherine West

Licence

MIT, except for some art assets by kenney.nl (see licence in folders)