fix(snow): use world space vectors

[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 title 'fix(snow): use world space vectors' directly aligns with the main change: transforming projection direction to world space to fix snow appearing on vertical surfaces.

✨ 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: 520945a
Using base ref: 520945a
Base commit date: 2025-12-03T01:43:28-08:00 (Wednesday, December 03, 2025 01:43 AM)
No actionable suggestions for changed features.

[github-actions]

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

[alandtse]

Please confirm testing results.

[midona-rhel]

Please confirm testing results.

I have now confirmed both brendan and mirirs issue is fixed. See the testing thread to replicate the issue, it is fairly simple, the castle you just download and add the modified esp, then go south and check that there is no snow on the walls. For anyone reviewing this see the discord testing release thread.