solvecraft/docs/render-cpu-advanced-integration.md

Advanced CPU recovery on the rendering branch

This document records the recovered local CPU port onto the personal branch's CPU/GPU2 snapshot. That recovery did not merge an upstream branch or change the document format. Subsequent numerical persistence and progressive publication are described below and in CPU progressive sampling. The recovery baseline is source tree 338535736593a8e49d9a6d1ccff8509dff618721, with Git HEAD 93a2922c5ee272fb605703ae84c05825b4a74607.

The recovery input is the 34-path local patch against original base 64339aedbc5e2f0d46e89dd915724deb06d5702d; its SHA-256 is 746f4e18b75ae9e6e4095e7c40812bad92c20078275979e2ccef7b3605924b77. It contains the project's original CPU prototypes and follow-ups associated with 0xlillith's prior work. This integration adds no third-party assets, code, rendering library or dependency. The source identity is provenance, not proof that its old tests passed on this new combination.

Historical recovery capabilities

The following table records the original recovery tree above, not the complete published renderer. Current Path Glass, coats, saved maps, adaptive sampling and qualification are listed in renderer parity. In particular, the current legacy box certificate accepts valid tiled box faces; it does not require exactly 12 triangles. Historical test/provenance claims below stay scoped to their recorded source.

Area	Original recovery consumer	Original recovery limits
GGX visible-normal sampling (VNDF)	CPU ImageTask rough reflections and the certified anisotropic adapter	The original single-scattering Schlick/GGX/separable-Smith model; no layered coat transport, transmission proposal or diffuse GI.
Fixed primary AA	Existing CPU image job and visible 1/4/16 sample controls	Reuse only for completed, nonselected primary hits within one fixed spatial sample. Not a progressive sample prefix.
Surface emission	Primary and reflected hits add visible linear radiance through current throughput	No mesh-light sampling, illumination of neighbors, emissive GI or calibrated watts.
Surface effects	The shared CPU hit surface feeds existing direct lights, HDR and opaque reflections	Bounded periodic roughness/bump fields in world millimetres; no geometry displacement, texture lookup or physical-material change.
Dielectric preview	Existing CPU image job branches bounded reflected/transmitted paths	Only certified thin sheets and outward, axis-aligned 12-triangle boxes; no general closed mesh, nested/touching volumes, colored transmission shadows, caustics or GI.
Recovered film component	Public FilmAccumulator API, with a complete-pass view and FilmPngTask encoder	This statistical component remains independent. The subsequent native progressive image path uses film::primary::PrimaryFilm and the shared image host.

The runtime API accepts new CPU options under raytrace: emissions, surface_effects, dielectrics and environment. The last is constant secondary radiance, separate from the captured HDR input at the top level. The subsequent CPU workspace panel exposes body reflections, constant secondary radiance, captured HDR input, directional lights and point lights. Area lights, area sampling/seed and spot cones have no dedicated panel editors, but complete saved numerical setups retain their values and pass them to engine validation. Emission, surface effects, glass and anisotropic face bindings remain runtime API inputs, outside portable setup persistence. Existing CPU primary AA, exposure, shadow and studio preset controls remain in place. The GPU material editor owns a different runtime schema selected explicitly with top-level progressive: true. CPU progressive sampling instead uses raytrace.progressive and supports the existing rectangular/continuous LED light integral with a fresh film-aware sample identity. The subsequent progressive continuation also accepts the existing certified thin-sheet/axis-aligned-box dielectric and planar anisotropy subsets, preserving all geometry, HDR, clear-coat and optical-overlap checks.

See VNDF, primary AA, emission, surface effects and dielectrics for request and numerical bounds.

Film and exact PNG contract

FilmAccumulator keeps per-pixel sample counts, linear means and Welford variance. Each checked update contains at most 256 consecutive pixels. Work and input checks precede its bounded commit, and cancellation is checked before commit. complete_pass refuses zero samples or unequal pixel counts and returns a borrowed immutable view. No partially completed pass is publishable through that API.

FilmPngTask resolves the complete linear mean with exposure, the existing Reinhard mapping and one sRGB transfer. It reuses the CPU PNG encoder, including the sRGB chunk, rather than introducing another codec. Its maximum output is 4096 pixels per dimension and four million pixels in total. A step resolves at most 256 pixels and writes at most four encoding rows. The encoded result owns its host reservation and exposes bytes by borrow.

The subsequent CPU progressive image path connects its camera-specific PrimaryFilm to sampler passes, the same cancellation token and cumulative work counter, generation checks under the host's publication lock, and retained immutable checkpoints. Only the final PNG is exportable. It does not call the statistical FilmAccumulator/FilmPngTask API described above. That independent API still expects an existing caller-owned film lease, held for the entire film lifetime; its component tests alone do not qualify the integrated progressive path.

CPU/GPU compatibility and resources

The builtin CPU image limit stays 384 MiB per job; registered GPU jobs keep their 512 MiB limit. Film snapshots use the existing host pool, reject a registered executor, and account for both borrowed film and encoding capacities before allocation. Completed PNGs retain the remaining lease. New emission, surface and dielectric option capacities are included in task and retained-request accounting. No new process, background worker, device registry or pool is introduced.

The shared OpaqueSurface type can contain GPU2's clear coat. Applying a CPU roughness field preserves that layer for direct BRDF evaluation. A coated body or face selected for CPU reflections, anisotropy or dielectrics is explicitly refused because the recovered transport estimator has no coat lobe. GPU2's own coat and dielectric path remains unchanged. Captured GPU transmission data is not reinterpreted as CPU dielectric options.

CPU admission still certifies immutable captured body identities, retains opaque body/face alpha requirements, checks finite inputs and bounded capacities, and rejects unsupported intersections between optical, emission and surface selections. Geometry, document history, physical mass properties and saved materials are not modified by these runtime inputs.

Validation status and next acceptance gate

The recovery handoff was a source-only port. At that handoff, its author ran Rust formatting, a whitespace check and a reproducible patch replay; the author did not run a Cargo build, test, Clippy, wasm check, application launch or native image acceptance for that isolated port. Existing recovered tests are retained, with new integration regressions for preservation of clear coat, refusal of unmatched coat transport and exclusion of registered executors from CPU film reservations.

Subsequent integration has executed CPU renderer, saved-document and engine regressions, default-feature host metadata/digest checks, and an earlier-snapshot Render workspace suite with CPU enabled and a real GPU required. That earlier workspace result does not qualify the new combined CPU additions. The workspace suite includes an actual CPU Render action and export of that job's retained native master; see CPU output presentation for the exercised scope. The source-only qualification above describes the original recovery handoff.

Each final combined revision still needs its repository-wide and platform checks, including wasm, plus native equal-camera image acceptance. Historical results from earlier source snapshots do not qualify later changes.

The optional CPU opaque path lighting consumer is part of the combined source and has executed renderer regressions. It adds bounded progressive diffuse/specular GI only when path is authored; existing restrictions and bytes above describe the absent-path route. Mixed glass/anisotropy/volume parity and combined document/engine/UI/native qualification remain incomplete.