PBR 3D viewer polish — IBL controls, material inspector

ADR 0028 Accepted ux · May 30, 2026

Related ADRs

• ADR 0017 — Monetization model + technical license enforcement

Referenced by

• ADR 0039 — Native viewers for proprietary DCC formats — clean-room, Blender-augmented, premium
• ADR 0069 — Preview rendering via headless three.js; Blender demoted to proprietary-format converter

Related roadmap phases

• Phase 1.18.B-10
• Phase 1.18.B-16
• Phase 1.18.B-8
• Phase 1.36

Tags

• ux
• ai
• 3d

Context

Phase 1.18.B-10 shipped the native 3D viewer (glTF / GLB / OBJ / FBX / Marmoset .mview, camera presets, IBL lighting, turntable poster, wireframe / UV inspect). The internal Marmoset-viewer reference and internal studio review processes both want a deeper PBR inspection layer: real-time material parameter tweaking, IBL environment switching from a curated set, per-material visibility, and direct comparison between two materials on the same mesh.

This is the polish pass that makes the viewer a real tool, not a preview.

Decision

Add Phase 1.36 — PBR 3D viewer polish — extending the existing ModelView.svelte host body with an inspector panel.

Inspector panel

A right-side panel in the asset viewer’s review mode:

• Materials list. Every material in the loaded model is listed with its texture maps. Click a material to focus it; per-material visibility toggle (hide / solo).
• Per-material parameters. Editable PBR params — base color, metallic, roughness, normal strength, emissive — with the change applied live to the WebGL scene. Resetting reverts the local override; the source asset is never written.
• Texture map preview. Each map (base color, normal, ORM / roughness, metallic, ao, emissive, opacity) has a thumbnail click- expand that opens the texture inspector (Phase 1.18.B-16) on that map specifically.
• IBL environment selector. Curated set of 8 HDR environments (studio / outdoor noon / outdoor sunset / overcast / indoor warm / indoor cool / dark room / pure white) plus a “use a project HDR” picker. Bound to the existing HDR / EXR preview pipeline.
• Material comparison. Pick two materials in the list, A / B wipe (reusing the 1.18.B-8 A/B compare primitives) over the same mesh.
• Wireframe / UV / normal overlay. Already shipped in 1.18.B-10; the inspector adds per-material wireframe (rather than whole-mesh).

Output

The inspector’s overrides can be exported as a material_review.json file attached to the post — a structured comment that says “the roughness on this material should be 0.4, not 0.7” without the reviewer needing to write prose.

Per-tier behaviour

PBR inspector is available to all tiers (same-feature, scale-only differentiation per ADR 0017). The license tier caps the count of loaded materials inspected in parallel via the tangled-derivation model.

Consequences

Positive

• The 3D viewer crosses from “preview” to “review tool” — actual art-direction work happens in-product.
• The override-as-JSON output is structured feedback that survives the conversation; engineers ingesting reviews don’t have to parse comment prose.

Negative

• WebGL parameter binding to PBR params is non-trivial; uses three.js MeshStandardMaterial properties + a small reactive store.
• IBL environments need to be packaged with the binary (~30 MB HDRs) or fetched on first use. Mitigation: fetch-on-use with cache (saves binary size).

Alternatives considered

• Just embed the Marmoset Toolbag viewer for everything. Marmoset is closed-source and would re-introduce a closed-source dependency we’ve otherwise avoided (ADR 0017). The native viewer covers most use cases; .mview shipping is already there for the cases where Marmoset is what the artist uses.
• No live material editing; review-only. Loses the highest- value flow.

Reference

• Phase 1.36 in docs/roadmap.md.
• 3D viewer (Phase 1.18.B-10, shipped).
• Texture inspector (Phase 1.18.B-16).
• A/B comparison (Phase 1.18.B-8).