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
220 lines
8.8 KiB
HTML
220 lines
8.8 KiB
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<article data-uid="">
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<h1 id="entity-query-usage">Entity Query Usage</h1>
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<p>This page describes practical <code>EntityQuery</code> usage patterns from the runtime ECS API.
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For full API signatures, see the generated API pages under <code>doc/api/</code>.</p>
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<h2 id="overview">Overview</h2>
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<p><code>EntityQuery</code> is the main data access surface for ECS iteration in <code>Ghost.Entities</code>.</p>
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<ul>
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<li>Build a query once using <code>QueryBuilder</code> and reuse the query handle (<code>Identifier<EntityQuery></code>) across frames.</li>
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<li>Access query data in three common ways:
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<ul>
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<li><code>ForEach</code> for simple lambda-style iteration.</li>
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<li><code>GetEntityComponentIterator<T...>()</code> when you need entity IDs with component refs.</li>
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<li><code>GetChunkIterator()</code> for cache-friendly chunk-level traversal.</li>
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</ul>
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</li>
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<li>Schedule jobs (<code>IJobChunk</code> / <code>IJobEntity<...></code>) for parallel work.</li>
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</ul>
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<h2 id="minimal-setup">Minimal Setup</h2>
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<pre><code class="lang-csharp">using Misaki.HighPerformance.Jobs;
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using Misaki.HighPerformance.LowLevel.Buffer;
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var scheduler = new JobScheduler(4);
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var world = World.Create(scheduler);
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using var scope = AllocationManager.CreateStackScope();
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using var set = new ComponentSet(scope.AllocationHandle, ComponentTypeID<Transform>.Value);
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Span<Entity> entities = stackalloc Entity[1000];
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world.EntityManager.CreateEntities(entities, set);
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var queryID = new QueryBuilder().WithAllRW<Transform>().Build(world);
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ref var query = ref world.ComponentManager.GetEntityQueryReference(queryID);
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</code></pre>
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<h2 id="pattern-1-foreach-for-simple-iteration">Pattern 1: <code>ForEach</code> for Simple Iteration</h2>
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<p>Use <code>ForEach<T...></code> when you want concise in-place updates or debug output.</p>
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<pre><code class="lang-csharp">query.ForEach<Transform>((entity, ref Transform transform) =>
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{
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transform.position += new float3(1, 0, 0);
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});
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</code></pre>
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<p>Why this pattern:</p>
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<ul>
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<li>Fast to write and easy to read.</li>
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<li>Good for gameplay logic and quick data transforms.</li>
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</ul>
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<h2 id="pattern-2-entity--component-iterator">Pattern 2: Entity + Component Iterator</h2>
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<p>Use <code>GetEntityComponentIterator<T...>()</code> when you need both identity and mutable component data.</p>
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<pre><code class="lang-csharp">foreach (var (entity, transform) in query.GetEntityComponentIterator<Transform>())
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{
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transform.Get().position += new float3(0, 1, 0);
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}
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</code></pre>
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<p>Why this pattern:</p>
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<ul>
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<li>Explicit access to the entity in each iteration.</li>
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<li>Works well when you need side lookups keyed by entity.</li>
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</ul>
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<h2 id="pattern-3-chunk-iterator-for-throughput">Pattern 3: Chunk Iterator for Throughput</h2>
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<p>Use <code>GetChunkIterator()</code> for the most cache-friendly, low-overhead traversal.</p>
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<pre><code class="lang-csharp">foreach (var chunk in query.GetChunkIterator())
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{
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var transforms = chunk.GetComponentDataRW<Transform>();
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var entitiesInChunk = chunk.GetEntities();
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for (var i = 0; i < chunk.EntityCount; i++)
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{
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transforms[i].position += new float3(0, 0, 1);
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}
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}
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</code></pre>
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<p>Why this pattern:</p>
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<ul>
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<li>Minimizes per-entity overhead.</li>
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<li>Best fit for heavy simulation and broad data transforms.</li>
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</ul>
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<h2 id="parallel-job-scheduling">Parallel Job Scheduling</h2>
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<p><code>EntityQuery</code> supports chunk and entity parallel scheduling.</p>
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<p><code>IJobChunk</code> example:</p>
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<pre><code class="lang-csharp">internal struct MoveChunkJob : IJobChunk
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{
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public void Execute(ChunkView view, ref readonly JobExecutionContext ctx)
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{
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var transforms = view.GetComponentDataRW<Transform>();
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for (var i = 0; i < view.EntityCount; i++)
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{
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transforms[i].position += new float3(5, 5, 5);
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}
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}
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}
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var handle = query.ScheduleChunkParallel(new MoveChunkJob(), batchSize: 1, JobHandle.Invalid);
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scheduler.Wait(handle);
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</code></pre>
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<p>Notes:</p>
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<ul>
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<li>Ensure all dependencies are represented in the input <code>JobHandle</code>.</li>
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<li>Wait or chain handles before reading modified data on the main thread.</li>
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<li>Prefer chunk jobs for contiguous memory access patterns.</li>
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</ul>
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<h2 id="lifecycle-and-cleanup">Lifecycle and Cleanup</h2>
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<pre><code class="lang-csharp">world.EntityManager.DestroyEntities(entities);
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world.Dispose();
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scheduler.Dispose();
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JobScheduler.ReleaseTempAllocator();
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</code></pre>
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<p>If your test or app creates worlds/schedulers manually, always clean them up in deterministic order.</p>
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