perf: optimise shadows

[doodlum]

Summary by CodeRabbit

• Refactor
  • Enhanced shadow filtering implementation by replacing Poisson disk-based sampling with PCF-style shadow filtering, delivering improved performance and more consistent shadow quality.
  • Streamlined dual-paraboloid shadow mapping with optimized filtering helpers.
  • Reduced shader code complexity for faster compilation and smaller file sizes.

[coderabbitai]

📝 Walkthrough

Walkthrough

Refactored shadow visibility filtering in Utility.hlsl by replacing Poisson disk-based GetPoissonDiskFilteredShadowVisibility functions with two new PCF-style helpers: SampleShadowPCF and SampleDualParaboloidShadowPCF. The new functions use 8 unrolled spiral sample offsets with rotation and radius scaling instead of seeded offset generation.

Changes

Cohort / File(s)	Summary
Shadow Filtering Refactoring package/Shaders/Utility.hlsl	Removed two GetPoissonDiskFilteredShadowVisibility overloads and added SampleShadowPCF and SampleDualParaboloidShadowPCF helpers. Updated main call sites to use new PCF sampling with SpiralSampleOffsets8 rotated samples. Removed seed-based offset generation and noise range transformation logic. Updated dual-paraboloid UV remapping formatting.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• perf: optimize utility and diffuseiblcs #1346: Directly related refactoring of shadow filtering—the prior PR modified GetPoissonDiskFilteredShadowVisibility, while this PR removes it entirely in favor of new PCF helpers.

Suggested reviewers

• alandtse
• jiayev

Poem

🐰 Shadow sampling code, hops in new ways,
Poisson disks gone, PCF saves the day,
Eight spiral samples twirl and rotate,
Filtering shadows, the hoppy new fate! 🌙

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title 'perf: optimise shadows' accurately reflects the main change—replacing Poisson disk filtering with simpler PCF-style sampling to improve performance.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch shadow-opt

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No actionable suggestions for changed features.

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

package/Shaders/Utility.hlsl (1)

620-644: ⚠️ Potential issue | 🟠 Major

PB path incorrectly clamps upper half of shadow samples — use SampleShadowPCF instead.

In the RENDER_SHADOWMASKPB case, shadowMapUv is computed across the full [0,1] range (line 628: lightDirection.xy / lightDirection.z * 0.5 + 0.5), which matches the layout of a single-paraboloid shadow map. However, line 638 calls SampleDualParaboloidShadowPCF(..., lowerHalf=false), which internally applies:

uv.y = min(uv.y, 0.5);

This caps all samples to y ≤ 0.5, collapsing the filter footprint onto a horizontal line whenever shadowMapUv.y > 0.5. The effect is visible as incorrect shadowing in the upper hemisphere of the single-paraboloid map—a horizontal seam or band where filtering breaks down.

By contrast, line 636 (SHADOWFILTER==1) samples the full unclamped range, so SHADOWFILTER==3 will produce visibly different shadows.

Fix: Use SampleShadowPCF instead, which applies no y-clamping and is designed for single-paraboloid layouts. Alternatively, pre-remap shadowMapUv.y to [0, 0.5] before the call, mirroring the RENDER_SHADOWMASKDPB pattern on line 656.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@package/Shaders/Utility.hlsl` around lines 620 - 644, In the
RENDER_SHADOWMASKPB branch you must stop using SampleDualParaboloidShadowPCF
(which clamps uv.y) and call SampleShadowPCF instead so the full shadowMapUv
range is sampled; locate the call to SampleDualParaboloidShadowPCF in the block
that computes shadowMapUv and shadowVisibility and replace it with
SampleShadowPCF passing the same sampler/params (shadowMapUv,
EndSplitDistances.x, shadowMapCompareValue, rotationMatrix, ShadowSampleParam.z,
false) or otherwise mirror the RENDER_SHADOWMASKDPB pattern (remapping uv.y to
[0,0.5]) if you prefer clamping — ensure shadowVisibility is set from
SampleShadowPCF rather than SampleDualParaboloidShadowPCF.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Outside diff comments:
In `@package/Shaders/Utility.hlsl`:
- Around line 620-644: In the RENDER_SHADOWMASKPB branch you must stop using
SampleDualParaboloidShadowPCF (which clamps uv.y) and call SampleShadowPCF
instead so the full shadowMapUv range is sampled; locate the call to
SampleDualParaboloidShadowPCF in the block that computes shadowMapUv and
shadowVisibility and replace it with SampleShadowPCF passing the same
sampler/params (shadowMapUv, EndSplitDistances.x, shadowMapCompareValue,
rotationMatrix, ShadowSampleParam.z, false) or otherwise mirror the
RENDER_SHADOWMASKDPB pattern (remapping uv.y to [0,0.5]) if you prefer clamping
— ensure shadowVisibility is set from SampleShadowPCF rather than
SampleDualParaboloidShadowPCF.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 3105647f-f37d-4c8d-9429-be58f1c721e1

📥 Commits

Reviewing files that changed from the base of the PR and between c150dfd and a970bea.

📒 Files selected for processing (1)

• package/Shaders/Utility.hlsl

[github-actions]

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