a2a1e5916d
Replace over-cap full sorting with a retained exact top-k heap while preserving the accepted tie-order fallback. Differential tests lock randomized and Town Network-scale output, and the measured 463-light path cuts selector CPU by 29 percent without warmed allocations.
61 lines
2.3 KiB
Markdown
61 lines
2.3 KiB
Markdown
# Slice H-b — exact bounded point-light selection
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## Result
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`LightManager.BuildPointLightSnapshot` no longer sorts every qualifying light
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when more than 128 lights are eligible. It keeps the best 128 in a retained
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worst-first heap, sorts only those 128 for submission, and performs no
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allocation after warm-up.
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The optimization preserves the accepted pre-slice output exactly:
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- dynamic lights still precede static lights;
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- each pool is still ordered by squared player distance;
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- the visible-cell, lit-state, and directional-light filters are unchanged;
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- in-budget snapshots remain in registration order;
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- equal-rank overflow frames which could expose .NET's unstable sort retain
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the previous complete-sort path and exact object-reference order.
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The retail oracle and readable pseudocode are in
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`2026-07-25-slice-h-b-light-top-k-pseudocode.md`. Retail's own selector is a
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bounded ordered insertion into separate static and dynamic pools. This slice
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ports the bounded-work principle without claiming to close AP-85's larger
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pool/cap/lifecycle divergence.
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## Evidence
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Focused conformance covers:
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- exact randomized differential comparison against the previous full-sort
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oracle;
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- equal-distance overflow and cap-boundary behavior;
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- lit, directional, dynamic, static, and visible-cell filtering;
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- a deterministic 463-light Town Network-scale candidate set;
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- zero warmed allocations on both bounded and equal-rank fallback routes.
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A Release diagnostic microbenchmark ran 100,000 snapshot builds with 463
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eligible uniquely ranked lights:
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| Route | Elapsed | Managed allocation |
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|---|---:|---:|
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| previous complete sort | 1,377.578 ms | 0 bytes |
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| retained bounded selector | 976.993 ms | 0 bytes |
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That sample is a 1.410x throughput improvement, or about 29.1% less CPU time
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inside selection. It is a narrow microbenchmark rather than a whole-frame FPS
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claim; its purpose is to prove that the replacement removes work rather than
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merely moving it.
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## Safety boundary
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No shader, light parameters, candidate membership, draw order, or production
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scene ownership changed. AP-85 remains open because retail's exact
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7-dynamic/40-static pools and DBObj-resident cell lifecycle are outside this
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performance-only slice.
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G4's independent visual rollback remains:
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```text
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git revert ef1d263337997bb030eadb7b8e71d73dc659907a
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```
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