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Save only lens parameters on existing CPU/GPU jobs while keeping unrelated draft settings dirty. Retain pinned checkpoints through preview and status, and release host-only snapshots outside the status lock. Use the admitted PNG bound for registered-executor checkpoint slots. Preserve executor work credits, final publication and regrade ownership. Add regression coverage and align help, translations and capability documentation.
105 lines
6.9 KiB
Markdown
105 lines
6.9 KiB
Markdown
# CPU bounded Atmosphere
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This implementation and its renderer, host-ownership, document/engine and pointer
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regressions are in published source `00edaf6a`/tree `38a7f0af`, tested by CI7.
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Full CI7 remains red. Native Atmosphere/Glass image quality and performance are
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not established by the opaque Sample Plate capture. See
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[qualification](render-parity.md#qualification).
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CPU Indirect lighting may consume the existing `HomogeneousVolume` contract: one
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world-space axis-aligned box, scalar extinction in inverse millimetres, RGB
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single-scattering albedo, and HG phase bias using propagation directions. It is the
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same bounded fog domain used by GPU Atmosphere, not a weather model, density grid,
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heterogeneous medium, spectral solver or emissive volume.
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The portable field is `CpuJob.volume`; the runtime field is
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`raytrace.volume`. Both preserve `min_mm`, `max_mm`, `extinction_per_mm`,
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`scattering_albedo` and `anisotropy`. Coordinates stay within ±1e9 mm, each extent
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is at least 1e-6 mm, extinction is 0–1000/mm, each albedo component is 0–1 and phase
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bias is −0.95–0.95. Existing image, geometry, cumulative work, memory, ray-distance,
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codec, 4096-byte host task and 1024-byte completion metadata caps remain unchanged.
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Those layout assertions compiled in the published CI7 source; the passing scoped
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renderer suite does not establish native Atmosphere image quality or performance.
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Positive extinction requires explicit progressive CPU Indirect lighting. It cannot
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combine with Glass, selected-medium subsurface scattering or surface Denoise.
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Existing selected-reflection/anisotropy Path restrictions remain in force. No
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setting is silently cleared, no fixed saved sampling is adopted automatically, and
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an unsupported request fails with its authored values retained. CPU has one Path
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attempt per film ordinal; GPU-specific Fresnel-stratum controls are not introduced
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as CPU transport parameters. Zero extinction stays authored while bypassing all
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new worker phases, random dimensions and heap owners. Omitted volume keeps the old
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serialized CPU wire. Literal fixed layout/admission byte identity with an older
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binary is not claimed.
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## Physical transport and model visibility
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A perspective ray uses its actual eye or sampled pupil as the optical start, so
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fog before the model near plane is not lost. Its original model near interval is
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retained. For orthographic projection, the optical start is the earlier of that
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original model near plane and the fog box's signed line entry; the model interval
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moves by the same ray parameter. The pixel line, camera, captured geometry, model
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bounds and framing never move. Far optical queries include the box even when it
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extends ahead of or beyond the model, or when the scene contains no model at all.
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A box extending beyond an actual admitted infinite-ray distance refuses explicitly.
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The single finite path samples an exponential flight within the forward ray/box
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segment, before its closest visible model or analytic-emitter endpoint. A collision
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applies RGB scattering albedo once, contributes foreground coverage, counts one
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Path event and evaluates direct lighting with the HG phase function. Continuation
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uses the shared exact HG sampler. Surviving sampled paths carry no-event probability
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in their endpoint density without multiplying throughput a second time. Absorption
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is represented by the complementary probability and scattering albedo; it is not
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an additional double attenuation.
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The existing bounded directional, point/spot, rectangle/LED and constant/HDR
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lighting continuations provide next-event samples. Volume vertices use their
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physical position and HG response/PDF; opaque vertices retain the completed
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Effects→Maps→Aging closure. Visibility is blocked by the same opaque geometry and
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other analytic emitters, and its box segment supplies transmittance to both the
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NEE contribution and matching phase/BSDF competitor density. Source sample counts
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and finite-depth endpoints retain complementary MIS. No new BRDF/PDF/clamp body or
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refracting-boundary approximation is added. The composed Sun/Sky stages use the same
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medium-aware response/PDF and physical source helper; combined phase/escape and
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SSS-delta regressions are included in the executed published renderer suite.
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Active-volume opaque launches use the existing exact producing-plane exclusion.
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A cooperative primitive-range walk charges one neighboring primitive per step,
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avoiding a surface normal offset that would change the fog length. Interior volume
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launches have no surface offset. An actual collision that aliases a source,
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endpoint or box boundary refuses rather than moving geometry or clipping radiance.
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## Work, retained ownership and prepared oracles
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One optional context lives in the already prepaid finite Path state. Actual State
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size pays pending source/event/range/MIS metadata; there is no ray tree, extra film,
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image plane, source image or decoder allocation. The inline runtime volume field
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adds a fixed request-header charge on every retained job, even for absent CPU
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options. Ordinary capture/preflight share the fixed metadata helper; regrade pays
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its own header once in the Record request lease and does not rebill the source
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HDR/texture bytes. This lease survives work release and an absent frame until the
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last status handle drops. Held frame/presentation metadata retains its existing
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separate lifetime. The composed Sun/Sky and inline volume headers are summed once.
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Every new worker operation debits before changing state. Box/free-flight/phase
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math is bounded, range discovery visits one primitive per debit, and traversal
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uses the existing cooperative cursors. Cancellation or work exhaustion cannot
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publish a late sample, checkpoint or master.
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Prepared regressions use independent exponential CDF, analytic slab/box lengths,
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HG formula/direction and light-sampling loops for depths 1/2/16. They cover pure
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absorption, a real perspective near prefix and pupil, orthographic foreground and
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background union, empty-scene coverage, single/multiple scattering, white-furnace
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energy, opaque blockers, finite rectangle and real nonconstant HDR sources with
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1/4/16/64 samples, survival-density MIS, exact physical source/range debits, every
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PNG prefix, raw FLOAT EXR/alpha, finishing, adaptive pilot separation, worker quanta,
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cancellation and retained-header release. Typed saved/runtime and cold-container
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Start/Undo tests preserve the camera, geometry and engineering materials. The
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shared Atmosphere adapter is composed with the celestial editor: one prospective
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method transaction preserves Volume, Sun, Sky, the analytic rig, camera and full
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authored sampling/output intent. A known volume-only edit retains mute/solo/light
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selection only with exact source provenance; unknown source replacement clears it.
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Actual pointer, save/Undo/cold and combined native Start/raw-master assertions are
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included in the published UI test module and CI7 execution. This is regression
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coverage, not native Atmosphere image-quality acceptance or a green full gate.
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