fix: use world space vectors for snow

[midona-rhel]

Fix snow appearing on vertical surfaces facing certain directions

Snow projection was comparing model-space and world-space vectors directly, causing inconsistent results based on
object rotation. Some wall-mounted objects (like rugs) would incorrectly show snow depending on which compass
direction they faced.

Fixed by transforming the projection direction to world space before the comparison.

Easiest way I found to replicate this was to download https://www.nexusmods.com/skyrimspecialedition/mods/18223 and create a new character, speedrun into the house and look at the rug facing the east.

Summary by CodeRabbit

• Rendering
  • Improved texture projection coordinate transformation in shader processing for enhanced visual accuracy.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

A shader optimization modifies how texture projection coordinates are transformed in the non-skinned PROJECTED_UV rendering path. Instead of directly using projection coordinates, the code now constructs a world-space 3x3 matrix from world axes and multiplies it with the projection vector, altering the orientation transformation.

Changes

Cohort / File(s)	Summary
Shader projection coordinate transformation package/Shaders/Lighting.hlsl	Modified TexProj computation in PROJECTED_UV (non-SKINNED) path to use world-space matrix transformation instead of direct texture projection coordinate usage

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Single file modified with focused mathematical transformation
• Requires understanding of world-space vs. texture-space coordinate systems and their impact on rendering
• Consider verifying the matrix construction logic and confirming this produces the intended visual/performance results

Possibly related PRs

• feat: always use worldspace lighting #1266: Moves projection/lighting math to world space in runtime code, complementing this shader-side world-space transformation

Suggested reviewers

• doodlum
• jiayev
• Pentalimbed

Poem

🐰 A matrix dance in shader's light,
World-space axes spinning bright!
Projections twist from old to new,
Transforming coordinates through and through. ✨

Pre-merge checks and finishing touches

✅ 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 PR title 'fix: use world space vectors for snow' directly matches the core change: transforming projection direction to world space for snow projection calculations, addressing the issue of snow appearing on vertical surfaces due to model-space/world-space mismatch.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[github-actions]

Using provided base ref: 39aa9d7
Using base ref: 39aa9d7
Base commit date: 2025-11-30T19:11:20-08:00 (Sunday, November 30, 2025 07:11 PM)
No actionable suggestions for changed features.

[github-actions]

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