refactor(epsilon constants): ♻️ standardize epsilon constants in HLSL shaders (#1227)

[IgorAlanAlbuquerque]

Add domain-specific epsilon constants to Math.hlsli and replace hardcoded values throughout the codebase for consistency and maintainability.

New constants added:

• EPSILON_GLINTS (1e-8f): For glints ellipse ratio calculations
• EPSILON_WEIGHT_SUM (1e-10f): For spherical harmonics weight normalization

Replacements:

• Skylighting.hlsli: 1e-10 → EPSILON_WEIGHT_SUM (rcp weight normalization)
• radianceDisocc.cs.hlsl: 1e-10 → EPSILON_WEIGHT_SUM (rcp weight normalization)
• Glints2023.hlsli: 1e-8 → EPSILON_GLINTS (ellipse ratio division)
• TerrainVariation.hlsli: 1e-6 → EPSILON_DIVISION (weight sum normalization)
• PBRMath.hlsli: 1e-6 → EPSILON_DIVISION (HairGaussian division guard)

Notes on deviations from the issue description:

• Common/BRDF.hlsli: 1e-6f occurrences were already replaced by EPSILON_DIVISION in PR fix: add checks to prevent NaN for BRDFs #1226. No changes needed.
• Common/PBR.hlsli: Most 1e-5 occurrences replaced by EPSILON_DOT_CLAMP. One remaining occurrence (max(luma, 1e-5) in GetHairDiffuseAttenuationKajiyaKay) was intentionally left unchanged — it guards luminance-based division, not a dot product clamp, and its value doesn't match EPSILON_DIVISION (1e-6f). Left for follow-up.
• DynamicCubemaps/DynamicCubemaps.hlsli: The hardcoded 0.00001 mentioned in the issue was not found in the current codebase. Left untouched.
• Skylighting/Skylighting.hlsli: Two occurrences of 1e-10 (unitSH / 1e-10) were intentionally left unchanged — they construct a large fallback value for the interior case, not weight normalization guards.
• ScreenSpaceGI/ScreenSpaceGI.hlsli and TerrainBlending/TerrainBlending.hlsli: The hardcoded 1e-4 values mentioned in the issue were not found in the current codebase. Left untouched.

Closes #1227

Summary by CodeRabbit

• Refactor
  • Standardized numerical precision constants across shader modules for improved consistency and maintainability in Screen Space GI, Skylighting, Terrain Variation, Glints, and PBR rendering calculations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 0d7391e4-b024-4afa-b3b5-4a96bfd7d5bc

📥 Commits

Reviewing files that changed from the base of the PR and between 354859c and 36b481b.

📒 Files selected for processing (6)

• features/Screen Space GI/Shaders/ScreenSpaceGI/radianceDisocc.cs.hlsl
• features/Skylighting/Shaders/Skylighting/Skylighting.hlsli
• features/Terrain Variation/Shaders/TerrainVariation/TerrainVariation.hlsli
• package/Shaders/Common/Glints/Glints2023.hlsli
• package/Shaders/Common/Math.hlsli
• package/Shaders/Common/PBRMath.hlsli

---

📝 Walkthrough

Walkthrough

This PR standardizes hardcoded epsilon values across multiple HLSL shader files by introducing domain-specific constants (EPSILON_GLINTS and EPSILON_WEIGHT_SUM) to Math.hlsli and replacing scattered literals with these named constants for improved consistency and maintainability.

Changes

Cohort / File(s)	Summary
Epsilon Constants Definition package/Shaders/Common/Math.hlsli	Added two new preprocessor macros: EPSILON_GLINTS (1e-8f) and EPSILON_WEIGHT_SUM (1e-10f) with minor formatting adjustments to existing macro definitions.
Weight Normalization & Division Protection features/Screen Space GI/Shaders/ScreenSpaceGI/radianceDisocc.cs.hlsl, features/Skylighting/Shaders/Skylighting/Skylighting.hlsli, features/Terrain Variation/Shaders/TerrainVariation/TerrainVariation.hlsli, package/Shaders/Common/PBRMath.hlsli	Replaced hardcoded epsilon values (1e-10, 1e-6) with named constants (EPSILON_WEIGHT_SUM, EPSILON_DIVISION) in division protection and weight normalization calculations, affecting threshold checks in reciprocal operations.
Glints Precision package/Shaders/Common/Glints/Glints2023.hlsli	Replaced hardcoded 1e-8 epsilon with EPSILON_GLINTS constant in ellipse ratio calculation for division-by-zero protection.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• skyrim-community-shaders#1226 — Implements the same epsilon standardization pattern with additional NaN prevention checks and discusses broader epsilon constant architecture.

Suggested reviewers

• alandtse
• jiayev

Poem

🐰✨ Constants hop in from the dark,
No more magic numbers scattered and stark!
EPSILON_GLINTS and WEIGHTS find their place,
In Math.hlsli's organized space!
Where precision meets purpose, oh what a delight,
The shaders now shimmer with standardized light! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Title accurately describes the main refactoring work: standardizing epsilon constants across HLSL shaders.
Linked Issues check	✅ Passed	PR addresses the core objective of issue #1227 by adding EPSILON_GLINTS, EPSILON_WEIGHT_SUM, and EPSILON_DIVISION constants and applying them across five shader files, though with documented deviations from the full scope.
Out of Scope Changes check	✅ Passed	All changes are directly related to standardizing epsilon constants in HLSL shaders as specified in issue #1227; no unrelated modifications detected.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

📝 Coding Plan

• Generate coding plan for human review comments

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[github-actions]

No actionable suggestions for changed features.

[github-actions]

✅ A pre-release build is available for this PR:
Download

[alandtse]

Thanks!