refactor(skylighting): simplify skylightingSH initialization

[jiayev]

This pull request refactors how the skylightingSH variable is initialized and used in the RunGrass.hlsl shader. The main improvement is to only declare and assign skylightingSH when skylighting is actually sampled, simplifying the code and reducing unnecessary variable declarations.

Shader logic simplification:

• Removed the static initialization of skylightingSH (unitSH_grass1 and unitSH_grass2) and now declares and assigns skylightingSH only when skylighting is sampled, making the code cleaner and reducing unnecessary assignments. (package/Shaders/RunGrass.hlsl, [1] [2]

Summary by CodeRabbit

• Bug Fixes

  • Improved grass skylighting calculation to ensure proper lighting in interior and exterior areas.

• Refactor

  • Optimized shader code structure for grass skylighting computation with reduced memory overhead.

[coderabbitai]

📝 Walkthrough

Walkthrough

The grass pixel shader's skylighting spherical-harmonics workflow is simplified by eliminating pre-initialized compile-time basis constants and directly initializing the skylightingSH variable from Skylighting::sample() calls within scoped branches.

Changes

Cohort / File(s)	Summary
Skylighting SH Initialization Refactor package/Shaders/RunGrass.hlsl	Removed static const SH basis declarations and changed initialization pattern: skylightingSH is now directly assigned from Skylighting::sample() within conditional branches instead of being pre-initialized to a basis value and conditionally reassigned.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• perf(ssgi): optimize  #1499: Directly overlaps with skylighting SH sampling and variable initialization changes in RunGrass.hlsl.
• chore: remove skylighting boost in favour of ibl #1447: Modifies related skylighting handling in RunGrass.hlsl, specifically how skylightingDiffuse is applied to directionalAmbientColor.
• fix: match grass brightness of vanilla #1801: Alters grass pixel shader skylighting and diffuse lighting computation in RunGrass.hlsl.

Suggested reviewers

• doodlum
• davo0411
• alandtse

Poem

🐰 A shader so clever, now lean and so tight,
No wasteful basis constants bloating the light,
Direct from the sample, the SH takes its place,
With scopes keeping order, we optimize grace! ✨

🚥 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 'refactor(skylighting): simplify skylightingSH initialization' accurately describes the main change—refactoring the skylightingSH variable initialization by removing static basis initialization and simplifying the assignment pattern.

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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 smallcleanup

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[github-actions]

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