JARVIGManual

ADR-0036 — Environment diffuse is scene lighting

Status: Accepted Date: 2026-09-23

Context

A face turned away from the directional, point, and spot lights goes black. That is the direct BRDF, not a bug in the gizmo. Filling it with color += vec3(0.1) would hide the missing term and would not change with the normal. Reflections, probes, and object bounce are later tickets. JRV-0071 already stores linear light above 1 before exposure.

Decision

The world owns one environment light. It is not a direct-light kind, not a material input, and not a render-view setting. The first source is two uniform hemispheres of linear radiance split by world +Y, plus an intensity and an enabled flag. There is no world position.

The shader adds Lambert diffuse irradiance after the direct loop:

baseColor * (1 - metallic) * ao * intensity * mix(lower, upper, normal.y * 0.5 + 0.5)

That product is diffuseAlbedo / π times the cosine-weighted irradiance of those hemispheres. Metallic removes it. AO scales it and does not scale direct light. The contribution is written into the existing Rgba16Float scene target, before exposure and tone mapping. The GPU packet is a separate 32-byte uniform, not one of the 64 direct-light records.

Disabled, the frame matches direct-only lighting. Camera motion does not change the packet.

Alternatives Considered

  • A constant ambient add. Rejected. It does not depend on the normal and it is not irradiance.
  • A cubemap or asset-imported HDRI in this ticket. Rejected. The asset database is not ready. The hemisphere is a bootstrap source with the same lighting meaning.
  • Stuffing the environment into the direct-light storage. Rejected. It has no position, no cone, and no view-space conversion.
  • Specular IBL, probes, or triangle-to-triangle bounce. Rejected. Those are JRV-0073, JRV-0074, and JRV-0075.
  • Darkening direct lights with AO. Rejected. JRV-0053 left AO off the direct term. It now applies to this indirect term only.

Consequences

docs/rendering/environment-lighting.md is the map. A pure metal stays dark away from direct light until JRV-0073 adds the indirect specular lobe. Geometry still does not exchange light. Emissive still does not light its neighbors.

Supersedes

Nothing. ADR-0028 still owns the surface. ADR-0029 still owns direct lights. ADR-0035 still owns the HDR target and the gizmo-after-tone-map order. This decision adds the first term that enters that target besides emissive and direct light.

Superseded By