perf(ISL): shift size bias calc to CPU

[sicsix]

Summary by CodeRabbit

• Refactor
  • Renamed light size-related properties to improve consistency across lighting features. This change does not affect user-facing functionality.

[coderabbitai]

Walkthrough

This change refactors the way light attenuation is calculated by renaming the size variable to sizeBias across relevant structures and shaders. The computation of the attenuation bias is updated to use a precomputed sizeBias value instead of recalculating it in the shader, streamlining the data flow from C++ to shader code.

Changes

Cohort / File(s)	Change Summary
Shader Attenuation Calculation Update features/Inverse Square Lighting/Shaders/InverseSquareLighting/InverseSquareLighting.hlsli	Modified the attenuation calculation to use light.sizeBias instead of computing from light.size.
Light Structure Member Rename features/Light Limit Fix/Shaders/LightLimitFix/Common.hlsli, src/Features/LightLimitFix.h	Renamed struct member size to sizeBias in both HLSL and C++ Light/LightData structures.
C++ Light Processing Update src/Features/InverseSquareLighting.cpp	Updated assignment to use and compute sizeBias for lights, matching the new shader expectations.

Sequence Diagram(s)

sequenceDiagram
    participant Cpp as C++ Light Processing
    participant Shader as Shader

    Cpp->>Cpp: Compute sizeBias = ScaledUnitsSq * size^2 * 0.5
    Cpp->>Shader: Pass Light struct with sizeBias
    Shader->>Shader: Use light.sizeBias in attenuation calculation

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• feat(ISL): added light size control #1342: Refactored the light size parameter to sizeBias and updated its usage in attenuation calculations, directly affecting the same logic and structures.

Suggested reviewers

• alandtse

Poem

A tweak to how our lights now gleam,
With sizeBias in the shader stream.
No more confusion, no more strife,
Just cleaner code and brighter life.
The rabbits cheer, the code’s precise—
Illuminating change is nice!
🐇✨

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📜 Recent review details

Configuration used: .coderabbit.yaml
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 93c4fef and c3039c7.

📒 Files selected for processing (4)

• features/Inverse Square Lighting/Shaders/InverseSquareLighting/InverseSquareLighting.hlsli (1 hunks)
• features/Light Limit Fix/Shaders/LightLimitFix/Common.hlsli (1 hunks)
• src/Features/InverseSquareLighting.cpp (1 hunks)
• src/Features/LightLimitFix.h (1 hunks)

🧰 Additional context used

🧠 Learnings (4)

📓 Common learnings

Learnt from: alandtse
PR: doodlum/skyrim-community-shaders#577
File: src/Features/WetnessEffects.h:36-36
Timestamp: 2025-06-08T11:25:14.536Z
Learning: In the skyrim-community-shaders project, boolean flags in C++ structs that interface with HLSL shaders use `uint` type instead of `bool` for compatibility reasons. This ensures consistent 4-byte size, proper 16-byte alignment in constant buffers, and cross-platform compatibility when passing data between C++ and HLSL shaders.

Learnt from: alandtse
PR: doodlum/skyrim-community-shaders#577
File: src/Features/WetnessEffects.h:36-36
Timestamp: 2025-06-08T11:25:14.536Z
Learning: In the skyrim-community-shaders project, boolean flags in C++ structs that interface with HLSL shaders use `uint` type instead of `bool` for compatibility reasons. This ensures consistent size, alignment, and cross-platform compatibility when passing data to shader constant buffers.

Learnt from: davo0411
PR: doodlum/skyrim-community-shaders#1070
File: src/State.cpp:79-83
Timestamp: 2025-05-30T11:44:15.542Z
Learning: In the Skyrim Community Shaders project, the `smoothDrawCalls` array in the `State` class is declared as type `double` in `src/State.h`, which is the correct floating-point type for performing exponential moving average smoothing calculations.

features/Light Limit Fix/Shaders/LightLimitFix/Common.hlsli (4)

Learnt from: alandtse
PR: #577
File: src/Features/WetnessEffects.h:36-36
Timestamp: 2025-06-08T11:25:14.536Z
Learning: In the skyrim-community-shaders project, boolean flags in C++ structs that interface with HLSL shaders use uint type instead of bool for compatibility reasons. This ensures consistent 4-byte size, proper 16-byte alignment in constant buffers, and cross-platform compatibility when passing data between C++ and HLSL shaders.

Learnt from: alandtse
PR: #577
File: src/Features/WetnessEffects.h:36-36
Timestamp: 2025-06-08T11:25:14.536Z
Learning: In the skyrim-community-shaders project, boolean flags in C++ structs that interface with HLSL shaders use uint type instead of bool for compatibility reasons. This ensures consistent size, alignment, and cross-platform compatibility when passing data to shader constant buffers.

Learnt from: alandtse
PR: doodlum/skyrim-community-shaders#0
File: :0-0
Timestamp: 2025-07-01T18:01:07.079Z
Learning: In the skyrim-community-shaders project, simple scalar constants in HLSL shaders use #define (e.g., #define NTHREADS 128), while more complex constants use static const within namespaces (e.g., Math namespace in Math.hlsli). For epsilon standardization, #define is the appropriate choice since epsilon values are simple scalar constants.

Learnt from: alandtse
PR: #577
File: features/Wetness Effects/Shaders/WetnessEffects/WetnessEffects.hlsli:57-61
Timestamp: 2025-06-17T05:40:22.785Z
Learning: Default parameter values are supported in the HLSL compiler used by the skyrim-community-shaders project, contrary to standard HLSL (FXC/DXC) limitations.

src/Features/LightLimitFix.h (1)

Learnt from: alandtse
PR: #577
File: src/Features/WetnessEffects.h:36-36
Timestamp: 2025-06-08T11:25:14.536Z
Learning: In the skyrim-community-shaders project, boolean flags in C++ structs that interface with HLSL shaders use uint type instead of bool for compatibility reasons. This ensures consistent 4-byte size, proper 16-byte alignment in constant buffers, and cross-platform compatibility when passing data between C++ and HLSL shaders.

features/Inverse Square Lighting/Shaders/InverseSquareLighting/InverseSquareLighting.hlsli (1)

Learnt from: alandtse
PR: doodlum/skyrim-community-shaders#0
File: :0-0
Timestamp: 2025-07-01T18:01:07.079Z
Learning: In the skyrim-community-shaders project, simple scalar constants in HLSL shaders use #define (e.g., #define NTHREADS 128), while more complex constants use static const within namespaces (e.g., Math namespace in Math.hlsli). For epsilon standardization, #define is the appropriate choice since epsilon values are simple scalar constants.

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• GitHub Check: Validate shader compilation (Flatrim, .github/configs/shader-validation.yaml)
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🔇 Additional comments (4)

features/Light Limit Fix/Shaders/LightLimitFix/Common.hlsli (1)

41-41: LGTM: Consistent renaming for performance optimization.

The renaming of size to sizeBias aligns with the PR objective to move size bias calculation to CPU. The struct layout remains unchanged, maintaining compatibility with C++ counterparts.

src/Features/LightLimitFix.h (1)

56-56: LGTM: Maintains shader interface compatibility.

The renaming to sizeBias is consistent with the corresponding shader structure and supports the performance optimization by enabling pre-computed bias values.

src/Features/InverseSquareLighting.cpp (1)

66-66: Excellent performance optimization—please verify the constant definitions

The move to precompute sizeBias on the CPU is mathematically correct and will reduce per-pixel work in the shader. However, searches didn’t locate definitions for ScaledUnitsSq or SCALED_UNITS_SQ in the codebase.

• Confirm that the C++ ScaledUnitsSq value exactly matches the HLSL SCALED_UNITS_SQ constant
• Ensure both are kept in sync (e.g., defined in a shared header or copied correctly)

features/Inverse Square Lighting/Shaders/InverseSquareLighting/InverseSquareLighting.hlsli (1)

15-15: Excellent shader optimization: Eliminates per-pixel calculations.

The change replaces SCALED_UNITS_SQ * light.size * light.size / 2.0f with the pre-computed light.sizeBias, eliminating 3 arithmetic operations per pixel. This directly addresses the PR objective of moving size bias calculation to CPU for better performance.

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[github-actions]

Using provided base ref: 93c4fef
Using base ref: 93c4fef
Base commit date: 2025-07-30T22:18:47-07:00 (Wednesday, July 30, 2025 10:18 PM)
No actionable suggestions for changed features.

[github-actions]

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