ara3d-authoring

Authoring Ara 3D Studio tools (generators & modifiers)

Ara 3D Studio users extend the app with standalone C# scripts. Drop a .cs file into the Scripts folder; Studio compiles it on save and surfaces every tool it finds in the UI with an auto-generated parameter panel. No project, no build step, no restart.

Two roles cover almost everything:

• Generator — makes new geometry from parameters. Implements IGenerator, has an Eval() that takes no geometry input.
• Modifier — transforms geometry flowing through the graph. Implements IModifier, has an Eval(input) that takes an upstream geometry object.

Everything below is the contract the host actually enforces (by reflection), followed by the attributes that shape the UI, the valid input/output types, deployment, and two worked examples.

Paths below are relative to the ara3d-sdk repo root (where this skill lives). A few cited files live in the Ara 3D Studio host app repo, not the SDK — those are marked (host repo).

1. The runtime contract (what the host requires)

The host wraps your object in EvaluatorWrapper and calls it by reflection. The rules:

1. Marker interface. Implement IGenerator or IModifier (namespace Ara3D.Studio.API). Both are empty marker interfaces — they only tag the class for discovery.
2. A public method named exactly Eval. The wrapper does type.GetMethod("Eval"). The name, casing, and public visibility all matter. Exactly one Eval per class.
3. Eval arguments define the input:
   • Generator: Eval() — zero geometry args. May take a single EvalContext.
   • Modifier: Eval(TInput) — the first parameter is the geometry it consumes. The host converts the upstream graph object to TInput (see §4).
   • Optional EvalContext may be added as an extra parameter (generator: the only arg; modifier: the second arg). Use it for RefreshUI, animation time, and host access.
4. Return type = output. Whatever Eval returns becomes the object flowing downstream and gets rendered. Must be a renderable/convertible geometry type (see §4).
5. Parameters = public fields or properties. Every public read/write field or property becomes an editable control in the panel. Read-only properties ({ get; private set; }) become non-editable read-outs.