fix(hooks): promote snow render targets to fp16 for banding

[doodlum]

Extracted from the effect11sh2 branch as the snowswap-hooks half of the "banding fix" pair.

Summary

kSNOW and kSNOW_SWAP are created at R8G8B8A8_UNORM by vanilla. The snow shader accumulates wetness/sparkle values that exceed the 8-bit range and quantize into visible banding on tessellated snow. Hook their CreateRenderTarget calls (offsets 0x406/0x41C in BSShaderRenderTargets::Create) and override the format to R16G16B16A16_FLOAT to give the snow pass enough headroom.

Mirrors the existing CreateRenderTarget_Main / CreateRenderTarget_Normals / CreateRenderTarget_NormalsSwap / CreateRenderTarget_MotionVectors pattern, sourced from the same RelocationID.

Scope note: sky noise half held back

The companion commit on effect11sh2 ("better banding fix" in Sky.hlsl) replaces a per-pixel TPDF noise term — which effect11sh2 had also added — with a multiplicative 1 + noiseGrad * 10 scheme. Neither the TPDF term nor that scheme exists on dev, where the DITHER path has been restructured around ENABLE_LL (linear lighting) since the original commit. Forward-porting the multiplicative noise into the ENABLE_LL-conditional path is a graphics tuning decision that needs runtime evaluation, so it's been left out of this PR rather than guessed at.

Test plan

• Build a Skyrim DLL and confirm tessellated snow no longer shows banding under varying sunlight.
• Confirm no visual regression on non-snow geometry (these RTs only feed the snow pass).
• Spot-check VRAM cost — going from R8 to R16 on these two RTs is small but non-zero.

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Generated by Claude Code

Summary by CodeRabbit

• New Features
  • Improved snow render target handling with enhanced visual quality through updated render format specifications.

[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 Plus

Run ID: e03e8ca3-44af-4145-bb55-6b191ae49467

📥 Commits

Reviewing files that changed from the base of the PR and between e259a92 and 82a9313.

📒 Files selected for processing (1)

• src/Hooks.cpp

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📝 Walkthrough

Walkthrough

This PR adds two new renderer hooks (CreateRenderTarget_Snow and CreateRenderTarget_SnowSwap) that override the format of snow-related render targets to R16G16B16A16_FLOAT floating-point format before delegating to the original render target creation logic. Both hooks are installed in the Hooks::Install() routine.

Changes

Snow Render Target Hooks

Layer / File(s)	Summary
Snow render target hooks src/Hooks.cpp	CreateRenderTarget_Snow and CreateRenderTarget_SnowSwap hook structs set render target format to fp16 format and delegate to original creation logic. Hooks are installed in Hooks::Install() alongside existing render target hooks.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• community-shaders/skyrim-community-shaders#1510: Directly conflicts by removing the CreateRenderTarget_Snow hook and related render-pass hooks on the same code paths.
• community-shaders/skyrim-community-shaders#2178: Related change to Hooks::Install() that modifies CreateRenderTarget_* hook registrations (removes Normals/NormalsSwap while this PR adds Snow/SnowSwap).

Suggested reviewers

• alandtse
• sicsix
• SkrubbySkrubInAShrub

Poem

🐰 Fresh snow hooks descend with float precision,
Render targets glow in fp16 vision,
Two new thunks installed with care,
Crystal clear now fills the air! ❄️

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix(hooks): promote snow render targets to fp16 for banding' clearly and concisely describes the main change—converting snow render target formats from 8-bit to 16-bit floating-point to address banding issues.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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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 claude/banding-fix-snow-rt-precision

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 OpenGrep (1.22.0)

OpenGrep fatal error (exit code 2): [00.12][ERROR]: Error: exception Unix_error: No such file or directory stat src/Hooks.cpp
Raised by primitive operation at UTmp.replace_named_pipe_by_regular_file_if_needed in file "libs/commons/UTmp.ml", line 145, characters 8-27
Called from Scan_CLI.replace_target_roots_by_regular_files_where_needed.(fun) in file "src/osemgrep/cli_scan/Scan_CLI.ml", lines 1086-1087, characters 19-65
Called from List_.fast_map in file "libs/commons/List_.ml", line 81, characters 17-20
Called from Scan_CLI.repla

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[github-actions]

No actionable suggestions for changed features.

[SkrubbySkrubInAShrub]

I lied.

[github-actions]

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