Misaki
d8a7b07624
- Refactor D3D12 backend and RenderGraph module - Update graphics RHI and core rendering components - Add Random.hlsl shader include - Regenerate API documentation and update user guides
89 lines
3.0 KiB
Markdown
89 lines
3.0 KiB
Markdown
# ECS Workflows
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This document outlines standard daily workflows for working within GhostEngine's ECS.
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## Creating Entity Queries
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To read or modify data, you first build an `EntityQuery`. You use the `QueryBuilder` struct to define inclusion and exclusion constraints.
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```csharp
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Identifier<EntityQuery> queryId = QueryBuilder.Create()
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.WithAll<Position>() // Must have Position
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.WithAny<Player, Enemy>() // Must have Player OR Enemy
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.WithNone<Dead>() // Must NOT have Dead structurally
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.WithDisabled<Renderable>() // Must have Renderable structurally, but it must be disabled
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.Build(world);
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```
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Queries are hashed and cached internally by the `ComponentManager`. Building the same query mask twice will yield the same `Identifier<EntityQuery>`.
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## Iterating Chunk Views
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Once you have a query, use `GetChunkIterator()` to traverse the unmanaged memory directly. This returns a `ChunkView` struct.
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Because the data is unmanaged, you can extract `Span<T>` and modify it with extreme speed.
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```csharp
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ref var query = ref world.ComponentManager.GetEntityQueryReference(queryId);
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foreach (var chunkView in query.GetChunkIterator())
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{
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// Get Read-Only Span
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ReadOnlySpan<Velocity> vels = chunkView.GetComponentData<Velocity>();
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// Get Read-Write Span
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Span<Position> pos = chunkView.GetComponentDataRW<Position>();
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// For loop for cache-aligned processing
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for (int i = 0; i < chunkView.EntityCount; i++)
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{
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pos[i].Value += vels[i].Value * dt;
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}
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}
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```
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> **Note:** Accessing data using `GetComponentDataRW<T>()` will automatically bump the internal version numbers for that component type in that specific chunk, allowing other systems to detect changes efficiently.
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## Entity Command Buffers (Structural Changes)
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In ECS, structural changes (adding/removing components, destroying entities) reorganize chunk memory. Doing this while iterating over chunks invalidates the memory layout.
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To safely defer structural changes, use an `EntityCommandBuffer`.
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```csharp
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// Get the world's main ECB
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var ecb = world.EntityCommandBuffer;
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foreach (var chunk in query.GetChunkIterator())
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{
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var entities = chunk.GetEntities();
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var healths = chunk.GetComponentData<Health>();
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for (int i = 0; i < chunk.EntityCount; i++)
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{
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if (healths[i].Value <= 0)
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{
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// Defer the destruction until Playback() is called
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ecb.DestroyEntity(entities[i]);
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}
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}
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}
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```
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At the end of the frame (or the end of the system group update), you must call:
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```csharp
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world.PlaybackEntityCommandBuffers();
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```
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### Multi-threading ECBs
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When using the `JobScheduler`, you can record deferred commands across multiple worker threads concurrently by requesting thread-local ECBs:
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```csharp
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int workerIndex = JobScheduler.CurrentThreadIndex;
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var threadEcb = world.GetThreadLocalEntityCommandBuffer(workerIndex);
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// Safely record structural changes from parallel jobs
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threadEcb.AddComponent<Dead>(entity);
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```
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