feat(lod): add gamma sliders

[jiayev]

This pull request adds gamma correction controls to the Level of Detail (LOD) blending system, allowing fine-tuning of gamma for terrain, objects, and object snow in addition to brightness. The changes include new shader parameters, UI controls, and serialization support for these gamma values, as well as updates to the shader logic to apply gamma correction during color blending.

Gamma correction support for LOD blending:

• Added new gamma parameters (LODTerrainGamma, LODObjectGamma, LODObjectSnowGamma) to the LOD blending settings struct in both the shader shared data (SharedData.hlsli) and C++ feature definition (LODBlending.h), with appropriate default values. [1] [2]
• Updated the serialization macro and ImGui UI in LODBlending.cpp to support the new gamma parameters, including new sliders for gamma adjustment and expanded brightness slider ranges.

Shader logic updates:

• Modified LOD blending code in Lighting.hlsl to apply gamma correction using the new parameters before brightness scaling for terrain, objects, and object snow. This ensures colors are adjusted for gamma as well as brightness during blending. [1] [2] [3] [4]

Summary by CodeRabbit

• New Features
  • Added gamma correction controls for LOD blending: separate gamma sliders for terrain, objects, and snow-affected objects (0.1–3.0), working alongside existing brightness controls for finer visual tuning.
• Chores
  • Settings for the new gamma controls are integrated so adjustments persist with other LOD blending options.

[coderabbitai]

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Walkthrough

Adds three gamma parameters (terrain, object, object-snow) to LOD blending: new fields in shader and C++ settings, shader logic switched from simple brightness multiplication to per-channel gamma correction followed by brightness, and C++ serialization updated to include the new fields.

Changes

Cohort / File(s)	Summary
Shader struct definition package/Shaders/Common/SharedData.hlsli	Added four float fields (LODTerrainGamma, LODObjectGamma, LODObjectSnowGamma, pad0) to LODBlendingSettings (additive layout change).
Shader implementation package/Shaders/Lighting.hlsl	Replaced brightness-only multiplications with gamma-corrected operations: color = pow(abs(color), gamma) * brightness in LOD object, LOD object snow, LOD terrain, and LOD land blend paths.
C++ settings definition src/Features/LODBlending.h	Added LODTerrainGamma, LODObjectGamma, LODObjectSnowGamma floats and a padding pad to LODBlending::Settings (defaults = 1).
C++ settings serialization src/Features/LODBlending.cpp	Updated serialization to include the three new gamma fields in the NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT mapping.

Sequence Diagram(s)

sequenceDiagram
    participant UI as UI Controls
    participant CPP as C++ Settings
    participant CB as Constant Buffer
    participant Shader as Pixel/Surface Shader

    Note over UI,Shader: Old flow (brightness-only)
    UI->>CPP: set LODBrightness
    CPP->>CB: upload brightness
    CB->>Shader: brightness
    Shader->>Shader: color.xyz *= LODBrightness

    Note over UI,Shader: New flow (gamma + brightness)
    UI->>CPP: set LODGamma & LODBrightness
    CPP->>CB: upload gamma, brightness
    CB->>Shader: gamma, brightness
    Shader->>Shader: color.xyz = pow(abs(color.xyz), LODGamma)
    Shader->>Shader: color.xyz *= LODBrightness

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20–30 minutes

• Verify each LOD blending path updated consistently (objects, object snow, terrain, land blend).
• Check use of abs() before pow() and handling of negative/NaN values.
• Confirm shader constant buffer alignment and padding matches C++ struct layout and packing.
• Validate serialization includes all new fields and defaults are correct.

Suggested reviewers

• alandtse
• doodlum

Poem

🐰 I hopped through code at break of dawn,
Adding gammas to make colors strong.
Pow and brighten, pixels cheer—
Three small tweaks, the view is clear.
A rabbit's nudge, and shaders hum along.

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat(lod): add gamma sliders' directly and clearly summarizes the main change: adding gamma correction controls to the LOD blending system through three new gamma parameters.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

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

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📥 Commits

Reviewing files that changed from the base of the PR and between d18772e and b79fc5b.

📒 Files selected for processing (4)

• package/Shaders/Common/SharedData.hlsli (1 hunks)
• package/Shaders/Lighting.hlsl (4 hunks)
• src/Features/LODBlending.cpp (1 hunks)
• src/Features/LODBlending.h (1 hunks)

🚧 Files skipped from review as they are similar to previous changes (4)

• src/Features/LODBlending.h
• package/Shaders/Common/SharedData.hlsli
• package/Shaders/Lighting.hlsl
• src/Features/LODBlending.cpp

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[github-actions]

Using provided base ref: 7a53214
Using base ref: 7a53214
Base commit date: 2025-11-16T19:03:02Z (Sunday, November 16, 2025 07:03 PM)
No actionable suggestions for changed features.

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (2)

src/Features/LODBlending.h (1)

28-31: Consider explicitly initializing the padding field.

The padding field maintains struct alignment with the shader-side definition, but it's not explicitly initialized. While default initialization to zero is likely guaranteed, explicitly setting float pad = 0; improves clarity and ensures deterministic values if the struct is inspected or serialized in debug scenarios.

Apply this diff to explicitly initialize the padding:

 	float LODTerrainGamma = 1;
 	float LODObjectGamma = 1;
 	float LODObjectSnowGamma = 1;
-	float pad;
+	float pad = 0;

src/Features/LODBlending.cpp (1)

18-20: Consider adding tooltips for gamma sliders to improve usability.

The gamma sliders would benefit from brief tooltips explaining their effect, similar to how the terrain vertex colors checkbox has a tooltip. This would help users understand that gamma values < 1.0 brighten (expand) midtones while values > 1.0 darken (compress) them.

Example implementation:

 	ImGui::SliderFloat("LOD Terrain Gamma", &settings.LODTerrainGamma, 0.1f, 3.f, "%.2f");
+	if (auto _tt = Util::HoverTooltipWrapper()) {
+		ImGui::Text("Adjusts midtone brightness. <1.0 brightens, >1.0 darkens.");
+	}
 	ImGui::SliderFloat("LOD Object Gamma", &settings.LODObjectGamma, 0.1f, 3.f, "%.2f");
+	if (auto _tt = Util::HoverTooltipWrapper()) {
+		ImGui::Text("Adjusts midtone brightness. <1.0 brightens, >1.0 darkens.");
+	}
 	ImGui::SliderFloat("LOD Object Snow Gamma", &settings.LODObjectSnowGamma, 0.1f, 3.f, "%.2f");
+	if (auto _tt = Util::HoverTooltipWrapper()) {
+		ImGui::Text("Adjusts midtone brightness. <1.0 brightens, >1.0 darkens.");
+	}

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📥 Commits

Reviewing files that changed from the base of the PR and between 8f51609 and d18772e.

📒 Files selected for processing (4)

• package/Shaders/Common/SharedData.hlsli (1 hunks)
• package/Shaders/Lighting.hlsl (4 hunks)
• src/Features/LODBlending.cpp (1 hunks)
• src/Features/LODBlending.h (1 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

**/*.{cpp,cxx,cc,c,h,hpp,hxx,hlsl,hlsli,fx,fxh,py}

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Files:

• src/Features/LODBlending.cpp
• src/Features/LODBlending.h
• package/Shaders/Common/SharedData.hlsli
• package/Shaders/Lighting.hlsl

src/**/*.{cpp,cxx,cc,h,hpp,hxx}

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Include robust error handling and resource management with graceful degradation in the plugin code

Files:

• src/Features/LODBlending.cpp
• src/Features/LODBlending.h

🧠 Learnings (1)

📚 Learning: 2025-08-03T18:37:19.690Z

Learnt from: jiayev
PR: doodlum/skyrim-community-shaders#0
File: :0-0
Timestamp: 2025-08-03T18:37:19.690Z
Learning: ISReflectionsRayTracing.hlsl and ISWorldMap.hlsl in the skyrim-community-shaders repository are image-space post-processing shaders that perform color sampling and blending operations that need proper linear color space handling for the linear lighting system. ISReflectionsRayTracing handles screen-space reflections and should use conditional Color::IrradianceToLinear/Gamma conversions similar to ISCompositeLensFlareVolumetricLighting.hlsl. ISWorldMap performs 7x7 color accumulation that should be done in linear space similar to the pattern used in ISSAOComposite.hlsl.

Applied to files:

• package/Shaders/Lighting.hlsl

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• GitHub Check: Validate shader compilation (VR, .github/configs/shader-validation-vr.yaml)
• GitHub Check: Validate shader compilation (Flatrim, .github/configs/shader-validation.yaml)
• GitHub Check: Build plugin and addons

🔇 Additional comments (3)

src/Features/LODBlending.cpp (1)

8-11: LGTM!

The serialization correctly includes all three gamma fields in the proper order matching the struct definition. The padding field is appropriately excluded from serialization.

package/Shaders/Common/SharedData.hlsli (1)

146-149: LGTM!

The gamma fields and padding are correctly added to the LODBlendingSettings struct. The memory layout aligns properly with the C++ side definition, ensuring correct data transfer to the GPU. The bool type in HLSL cbuffers is 4 bytes, matching the C++ uint, so the struct packing is consistent.

package/Shaders/Lighting.hlsl (1)

1832-1832: Verify gamma correction is applied in the correct color space.

The gamma correction uses pow(abs(baseColor.xyz), gamma) at four locations (lines 1832, 1846, 1948, 2045). While the pattern is consistent and the order (gamma before brightness) is correct for artistic control, consider verifying the color space assumptions:

1. Based on the retrieved learnings, this codebase requires careful linear color space handling for the linear lighting system.
2. At line 1811, Color::Diffuse() is called, which likely converts colors to linear space.
3. Applying a power function after linear conversion is mathematically valid for artistic brightness/contrast adjustment, but ensure this matches the intended visual outcome.
4. The use of abs() is necessary to prevent NaN with fractional exponents, but it could mask bugs where colors incorrectly go negative.

The implementation appears intentional for artistic gamma adjustment (power curve) rather than color space conversion, which is acceptable if that's the design intent.

Based on learnings

Also applies to: 1846-1846, 1948-1948, 2045-2045

[davo0411]

looks good

[github-actions]

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