fix(terrain helper): fix conflicting bit

[doodlum]

Summary by CodeRabbit

• Bug Fixes

  • Fixed inconsistent activation of terrain displacement, improving visual stability and reducing artifacts across scenes and settings.

• Refactor

  • Standardized feature-flag usage with clear descriptors, removing fragile magic values.
  • Synchronized feature descriptors across rendering and state systems for consistent behavior.
  • Hardened feature masking to better accommodate future expansions without impacting current visuals.

[coderabbitai]

Walkthrough

Moved the THLandHasDisplacement flag from bit 6 to bit 9 and updated code to use the named enum constant instead of hard-coded bit indices across shader and engine source files.

Changes

Cohort / File(s)	Summary of changes
Shader flag definition package/Shaders/Common/Permutation.hlsli	Changed ExtraFeatureFlags::THLandHasDisplacement from (1 << 6) to (1 << 9).
Engine state enum src/State.h	Added/updated State::ExtraFeatureDescriptors::THLandHasDisplacement = 1 << 9.
Feature usage updates src/Features/TerrainHelper.cpp	Replaced hard-coded bit-6 clears/sets with enum-based THLandHasDisplacement (cast to uint); updated comments to reflect bits 0–5 vs THLandHasDisplacement tracking any displacement (bit 9).

Sequence Diagram(s)

sequenceDiagram
    participant TH as TerrainHelper
    participant S as State (ExtraFeatureDescriptors)
    participant Tex as Texture inputs

    Note over TH,Tex: TerrainHelper inspects textures for displacement
    Tex->>TH: provide displacement presence per texture (bits 0-5)
    alt any displacement present
        TH->>S: set THLandHasDisplacement (bit 9)
    else no displacement
        TH->>S: clear THLandHasDisplacement (bit 9)
    end
    Note right of S: uses named enum value (1 << 9) instead of hard-coded bit index

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• chore(emat): auto detect terrain parallax #1545 — Also moves THLandHasDisplacement to bit 9 and replaces magic-number usage; directly overlaps this flag migration.
• feat: add Extended Translucency #678 — Reallocates bits 6–8 for ETMaterialModel, motivating moving THLandHasDisplacement off bit 6.

Suggested reviewers

• alandtse

Poem

Hop hop, flip the bits just right,
From six to nine, the flag takes flight.
Enums replace the number's whim,
Displacement tracked — neat and prim.
A rabbit cheers: the code's in sight. 🐇

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 succinctly indicates a fix in the terrain helper related to a conflicting bit and matches the changeset’s focus on correcting the displacement flag’s bit position, making it clear and relevant.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch th-fix

---

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• src/Features/TerrainHelper.cpp (1 hunks)

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🔇 Additional comments (3)

src/Features/TerrainHelper.cpp (3)

180-180: LGTM! Named constant improves maintainability.

The change from hard-coded (1 << 6) to the named enum State::ExtraFeatureDescriptors::THLandHasDisplacement improves code clarity and maintainability. The cast to uint is appropriate for bitwise operations.

---

183-183: Comment updated correctly.

The comment now accurately describes the bit allocation: bits 0-5 track individual texture displacement, and THLandHasDisplacement (bit 9) tracks whether any texture has displacement. This addresses the past review comment about the outdated reference to "constant 6".

---

188-188: LGTM! Consistent use of named constant.

The change is consistent with line 180, using the named enum constant instead of a magic number. The logic correctly sets the THLandHasDisplacement flag when any texture has displacement. The bitwise OR operation is idempotent, so setting the bit multiple times within the loop has no adverse effect.

---

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[github-actions]

Using provided base ref: 62fa347
Using base ref: 62fa347
Base commit date: 2025-10-12T14:53:26+01:00 (Sunday, October 12, 2025 02:53 PM)
No actionable suggestions for changed features.

[coderabbitai]

Actionable comments posted: 1

📜 Review details

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 62fa347 and e230647.

📒 Files selected for processing (3)

• package/Shaders/Common/Permutation.hlsli (1 hunks)
• src/Features/TerrainHelper.cpp (1 hunks)
• src/State.h (1 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

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

📄 CodeRabbit inference engine (.github/copilot-instructions.md)

Do not include TODO/FIXME placeholders; provide complete, working solutions

Files:

• package/Shaders/Common/Permutation.hlsli
• src/State.h
• src/Features/TerrainHelper.cpp

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

📄 CodeRabbit inference engine (.github/copilot-instructions.md)

src/**/*.{cpp,cxx,cc,h,hpp,hxx}: Ensure SE/AE/VR runtime compatibility; use runtime detection patterns (e.g., REL::RelocateMember())
Include robust error handling and resource management with graceful degradation in the plugin code

Files:

• src/State.h
• src/Features/TerrainHelper.cpp

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (3)

• 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 (4)

src/State.h (1)

165-165: LGTM! Bit position correctly avoids ETMaterialModel conflict.

The new bit position (9) avoids the conflict with ETMaterialModel which occupies bits 6-8. The change is properly aligned with the shader and C++ usage.

src/Features/TerrainHelper.cpp (2)

180-180: LGTM! Correctly uses named enum for clearing the displacement flag.

The code properly uses the named enum constant instead of a hard-coded bit position, and the uint cast is necessary for the enum class.

---

188-188: LGTM! Correctly sets the displacement flag using named enum.

The code properly uses the named enum constant, maintaining consistency with the enum definition in State.h and the shader constant in Permutation.hlsli.

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

75-75: LGTM! Shader constant aligned with C++ enum definition.

The bit position correctly matches the ExtraFeatureDescriptors::THLandHasDisplacement definition in src/State.h, maintaining consistency across the shader and C++ code.

[github-actions]

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

[alandtse]

Make sure to double check the rabbit.

[alandtse]

Is this backward compatible? @doodlum ? @hakasapl

[doodlum]

Is this backward compatible? @doodlum ? @hakasapl

Is this backward compatible? @doodlum ? @hakasapl

Yes