ParticleEmitterComponent uses RealityKit.VFXEmitter with a two-tier schema: top-level timing/shape/spawning on currentState, and particle properties inside mainEmitter/spawnedEmitter structs.

Details

Schema Architecture

The ParticleEmitterComponent maps to RealityKit.VFXEmitter in USDA. The schema uses a two-tier structure:

def RealityKitComponent "VFXEmitter" {
    uniform token info:id = "RealityKit.VFXEmitter"
    
    def RealityKitStruct "currentState" {
        // Emitter Tab fields (timing, shape, spawning)
        
        def RealityKitStruct "mainEmitter" {
            // Particles Tab fields (primary emitter)
        }
        
        def RealityKitStruct "spawnedEmitter" {
            // Secondary emitter (same schema as mainEmitter)
        }
    }
}

Why This Matters

This fixture set is too large to understand comfortably from prose alone. The current public source of truth should be:

• the schema page at /features/particle-emitter-component/schema
• the per-component exports under /api/components/particle-emitter-component/
• especially fixtures.csv, which flattens authored USDA rows by fixture path, UI section, struct scope, field name, and value

That is more trustworthy than repeating a hand-maintained total field count inside this note.

Sparse Authoring Pattern

The canonical baseline fixture is BASE.usda, and it shows no authored particle-emitter fields:

• All fields default to omitted in BASE.usda
• Fields are only written when they differ from their default or are explicitly set
• Variation fields (e.g., particleSizeVariation) co-author their base field when set
• Shape-specific fields (e.g., torusInnerRadius) only appear with matching shape selection
• Several other fixture files are baseline-equivalent scaffolds and should not be treated as the canonical baseline

Secondary Emitter

The spawnedEmitter struct shares the same schema as mainEmitter. The isSpawningEnabled bool on currentState gates whether spawnedEmitter fields are authored.

Notes

• The component prim is named VFXEmitter in USDA, not ParticleEmitter
• Internal USD type uses RealityKitStruct for nested state containers
• spawnedEmitter is not a separate schema; it mirrors the particle field layout used by mainEmitter
• The fixture set currently contains 108 .usda files