ZOA Rendering HDRP

HdrpRenderPipelineAdapter implements IRenderPipelineAdapter, reports "hdrp" and "High Definition Render Pipeline", and constructs an HdrpMaterialVariantResolver. Registering it with RenderPipelineAdapterRegistry and calling SetActive is all it takes to redirect every semantic resolution in the project.

HdrpMaterialMapping carries a shader name alongside the asset path, so a mapping can point at HDRP/Lit today and at HDRP/Hair or HDRP/Eye where a project needs the specialised shaders. HdrpFxMapping is wider than its URP counterpart: it holds both a VFX Graph asset path and a particle prefab path, because HDRP effects commonly exist in both forms. TryResolve returns the VFX Graph path, with the prefab available through GetMapping when the caller needs it.

Availability is a static switch here too: a test calls HdrpRenderPipelineAdapter.SetAvailability(false) to drive RenderingValidator into its RENDER_003 branch.

HdrpRenderPreviewService implements IRenderPreviewService over an internal dictionary of active contexts. CreatePreview mints a GUID-keyed PreviewContext for a visual profile and records it; ReleasePreview removes it from the dictionary and disposes it, which flips the context's IsActive to false.

The service is strict about preconditions and forgiving about cleanup. CreatePreview throws InvalidOperationException when HDRP is not available and ArgumentException when the profile id is invalid, but ReleasePreview accepts null without complaint. GetActiveContextCount and ReleaseAllPreviews exist so tooling can assert it is not leaking previews between editor sessions.

HdrpValidationService takes both resolvers in its constructor and validates by round-tripping. ValidateMappings iterates every registered material and effect id, resolves it, and records an issue when resolution fails or comes back with an empty asset path. The four codes it can produce are MATERIAL_RESOLUTION_FAILED, MATERIAL_EMPTY_PATH, FX_RESOLUTION_FAILED, and FX_EMPTY_PATH.

HdrpValidationReport wraps the resulting issues with the questions a build step actually asks: IsValid when there are no errors, HasWarnings, ErrorCount, WarningCount, and a ToString summary. ValidateVisualProfile is narrower, checking the profile id and warning when breaking visual deltas are on record that the profile has not been reviewed against.

The validation service seeds itself with nine HdrpVisualDelta entries covering ambient occlusion, global illumination, shadows, particle transparency, post-processing, subsurface scattering, hair, eyes, and cloth. Each records the URP behaviour, the HDRP behaviour, a severity, and a workaround.

Severity is the useful part. Cosmetic means the difference does not affect gameplay, Functional means it may affect play or experience, and Breaking means content or code has to change. Global illumination is the one entry marked Breaking, and ValidateVisualProfile raises PROFILE_HAS_BREAKING_DELTAS as a warning on any profile that has not been reviewed against it.

AddVisualDelta and ClearVisualDeltas extend or reset the list. ClearVisualDeltas restores the nine defaults; it does not leave the catalogue empty.

HDRP expresses fog density as a mean free path: the distance in metres at which transmittance falls to roughly one over e. URP and the built-in pipeline use a density coefficient instead, so applying a pipeline-neutral VisualEnvironmentState means converting between the two.

HdrpEnvironmentMapping.TryGetMeanFreePath is that conversion, and it lives in the engine-free assembly so it can be unit-tested without HDRP installed. For both exponential modes the mean free path is the inverse of the density, since both reach one over e at one over d. Linear mode is approximated as the end distance divided by three. The value is clamped between MinMeanFreePathMeters of 1 and MaxMeanFreePathMeters of 5000, and the method returns false when the state authors no applicable fog so the caller leaves the HDRP override untouched.

Under HDRP the pipeline-agnostic RenderSettings pass drives neither fog nor exposure, so HdrpVisualEnvironmentApplier covers both. It registers itself before scene load when GraphicsSettings.currentRenderPipeline is an HDRenderPipelineAsset, and owns a global volume named "[ZOA] VisualEnvironment (HDRP)" at priority 1000 carrying ColorAdjustments and Fog overrides.

Exposure maps to ColorAdjustments.postExposure, not to HDRP's Exposure override. HDRP's Exposure in Fixed mode sets an absolute EV100, which would misread ExposureEv's offset intent. ColorAdjustments shares URP's offset semantic, so the value maps one to one across both pipelines.

Two things are documented as unmapped. Ambient is skipped because HDRP derives ambient from its sky and static lighting sky, not from RenderSettings.ambientLight. The semantic skybox id is skipped because HDRP sky is volume-authored.