feat: vanilla fresnel

[jiayev]

This pull request introduces a new "Vanilla Fresnel" feature, providing advanced Fresnel and GGX-based physically-based rendering (PBR) specular reflection options, with extensive configurability and integration throughout the shader pipeline. The changes add new settings, update data structures, and modify lighting calculations in both general and grass-specific shaders to support these features. Additionally, the feature is integrated into the engine's feature management and configuration systems.

Major new feature: Vanilla Fresnel

• Added a new VanillaFresnel feature with configurable settings (GGX specular, dynamic cubemap conversion, eye handling, etc.), UI controls, and serialization support (src/Features/VanillaFresnel.cpp, features/Vanilla Fresnel/Shaders/Features/VanillaFresnel.ini). [1] [2]

Shader pipeline and lighting model updates

• Integrated Vanilla Fresnel settings into the shared shader data (SharedData::VanillaFresnelSettings), and updated the buffer to include these settings (package/Shaders/Common/SharedData.hlsli, src/FeatureBuffer.cpp). [1] [2] [3]
• Modified main lighting evaluation to use GGX microfacet specular when enabled, with dynamic cubemap support and special handling for eyes and complex materials (package/Shaders/Lighting.hlsl, package/Shaders/Common/LightingEval.hlsli). [1] [2] [3] [4] [5] [6] [7]
• Added a microfacet GGX specular calculation function and conditional logic to switch between Phong and GGX models (package/Shaders/Common/LightingEval.hlsli).

Grass lighting improvements

• Updated grass lighting to support Vanilla Fresnel and GGX specular, with correct F0 and roughness parameter handling, and reflectance output (features/Grass Lighting/Shaders/GrassLighting/GrassLighting.hlsli, package/Shaders/RunGrass.hlsl). [1] [2] [3] [4] [5] [6]

Engine integration

• Registered the new feature in the engine's feature list and included its settings in the feature buffer (src/Feature.cpp, src/FeatureBuffer.cpp). [1] [2] [3]

These changes collectively enable a more physically-accurate and configurable specular reflection model, improving visual fidelity and user control over rendering behavior.

Summary by CodeRabbit

• New Features

  • Added "Vanilla Fresnel" feature with optional GGX microfacet specular, persistent settings and UI, tunable F0/roughness, auto cubemap conversion and special handling for eye passes.
  • Grass rendering now always outputs a Reflectance target and uses roughness-driven specular/reflectance values.

• Bug Fixes / Behavior

  • Adjusted lighting pipeline: specular and environment accumulation/weighting change when Vanilla Fresnel or GGX-on-grass is enabled to preserve visual consistency.

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📝 Walkthrough

Walkthrough

Adds a VanillaFresnel feature with runtime settings and UI, exposes settings to shaders, implements GGX microfacet specular helpers and a VANILLA_FRESNEL lighting path, updates material/env handling in Lighting.hlsl, and switches grass rendering to use roughness and F0 for specular/reflectance.

Changes

Vanilla Fresnel Feature

Layer / File(s)	Summary
VanillaFresnel Feature Definition & Registration src/Features/VanillaFresnel.h, src/Features/VanillaFresnel.cpp, features/Vanilla Fresnel/Shaders/Features/VanillaFresnel.ini, src/Globals.h, src/Globals.cpp, src/Feature.cpp, src/FeatureBuffer.cpp	New VanillaFresnel feature type with nested Settings, JSON serialization, ImGui settings UI, global feature instance and registration, and feature-buffer serialization integration.
Shader Constant Buffer & Permutation/State Flags package/Shaders/Common/SharedData.hlsli, package/Shaders/Common/Permutation.hlsli, src/State.h	Adds VanillaFresnelSettings to SharedData::FeatureData for shader access and introduces an IsEye extra-flag in shader permutation/state descriptors for eye-specific handling.
BRDF Microfacet Specular & LightingEval Integration package/Shaders/Common/LightingEval.hlsli	Adds MicrofacetSpecular computing GGX D, Smith joint-approx G, and Schlick F; EvaluateLighting gains a VANILLA_FRESNEL branch using that helper with compensation/scaling and early return.
Grass Lighting Interface & Implementation features/Grass Lighting/Shaders/GrassLighting/GrassLighting.hlsli, package/Shaders/RunGrass.hlsl, features/Grass Lighting/Shaders/Features/GrassLighting.ini	Changes GetLightSpecularInput signature to accept roughness and F0, adds an optional GGX-on-grass BRDF path and legacy exponential fallback, computes F0/roughness in RunGrass, always emits Reflectance for grass path, and updates specular accumulation calls.
Main Lighting Material & Environment Properties package/Shaders/Lighting.hlsl	Conditions material F0/roughness setup and complex-specular handling on VANILLA_FRESNEL and runtime flags; adds EnableDynamicCubemapsConversion, envMask-weighted F0/roughness interpolation and clamps, and adjusts indirect/specular accumulation to avoid double-counting under vanilla Fresnel modes.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• community-shaders/skyrim-community-shaders#1327: Both PRs modify package/Shaders/Lighting.hlsl’s extended-material/EMAT specular pipeline.
• community-shaders/skyrim-community-shaders#1995: Related refactor around BRDF/F_Schlick and microfacet helpers using F0.
• community-shaders/skyrim-community-shaders#1147: Related changes in Feature::GetFeatureList and feature registry handling.

Suggested reviewers

• doodlum
• alandtse
• SkrubbySkrubInAShrub

Poem

I nibble at the shader code tonight,
GGX facets catch the morning light,
F0 and roughness tuned just right,
Grass glints where tiny pixels gleam,
A rabbit hops beneath the fresnel beam. 🐇

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 9.52% 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 'feat: vanilla fresnel' directly and clearly matches the primary objective of this PR, which is to add a new VanillaFresnel feature to the codebase. It accurately summarizes the main change.
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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[SkrubbySkrubInAShrub]

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[coderabbitai]

🧹 Nitpick comments (1)

src/Features/VanillaFresnel.cpp (1)

66-74: ⚡ Quick win

Honor the runtime toggles before setting the eye permutation bit.

UpdateEyePermutation() always does the eye-pass detection work, so the new eye-specific permutation split stays active even when Vanilla Fresnel or eye special handling is turned off. Please clear the bit and return early unless the feature is enabled through globals::features. As per coding guidelines, "Flag potential performance impacts on rendering performance when implementing graphics features and suggest user toggles for feature control" and "Access core systems and feature registry through globals::features and globals::d3d namespaces defined in src/Globals.h".

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/Features/VanillaFresnel.cpp` around lines 66 - 74, Update
UpdateEyePermutation so it first checks the runtime feature toggle(s) in
globals::features (e.g., the Vanilla Fresnel / eye-special-handling flags) and,
if the feature is disabled, clear the IsEyeDescriptor bit on
globals::state->permutationData.ExtraShaderDescriptor and return early; only
call IsEyePass and set the IsEyeDescriptor bit when the feature toggle is
enabled. This change touches UpdateEyePermutation, IsEyePass, IsEyeDescriptor
and globals::state->permutationData.ExtraShaderDescriptor and should ensure the
eye permutation split is only active when globals::features indicates it.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/Features/VanillaFresnel.cpp`:
- Around line 66-74: Update UpdateEyePermutation so it first checks the runtime
feature toggle(s) in globals::features (e.g., the Vanilla Fresnel /
eye-special-handling flags) and, if the feature is disabled, clear the
IsEyeDescriptor bit on globals::state->permutationData.ExtraShaderDescriptor and
return early; only call IsEyePass and set the IsEyeDescriptor bit when the
feature toggle is enabled. This change touches UpdateEyePermutation, IsEyePass,
IsEyeDescriptor and globals::state->permutationData.ExtraShaderDescriptor and
should ensure the eye permutation split is only active when globals::features
indicates it.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: b242c771-4297-4a35-850c-ced402f99412

📥 Commits

Reviewing files that changed from the base of the PR and between e7bfd47 and 87351d0.

📒 Files selected for processing (13)

• features/Grass Lighting/Shaders/Features/GrassLighting.ini
• package/Shaders/Common/LightingEval.hlsli
• package/Shaders/Common/Permutation.hlsli
• package/Shaders/Common/SharedData.hlsli
• package/Shaders/Lighting.hlsl
• package/Shaders/RunGrass.hlsl
• src/Feature.cpp
• src/FeatureBuffer.cpp
• src/Features/VanillaFresnel.cpp
• src/Features/VanillaFresnel.h
• src/Globals.cpp
• src/Globals.h
• src/State.h

✅ Files skipped from review due to trivial changes (3)

• package/Shaders/Common/Permutation.hlsli
• features/Grass Lighting/Shaders/Features/GrassLighting.ini
• src/Globals.h

🚧 Files skipped from review as they are similar to previous changes (7)

• src/FeatureBuffer.cpp
• package/Shaders/Common/LightingEval.hlsli
• package/Shaders/RunGrass.hlsl
• src/Feature.cpp
• package/Shaders/Common/SharedData.hlsli
• src/Globals.cpp
• package/Shaders/Lighting.hlsl

[doodlum]

do not merge yet