chore(grass collision): minor tweaks

[doodlum]

Summary by CodeRabbit

• Bug Fixes

  • Grass collision now smoothly fades with distance to reduce popping at range.
  • Prevented upward movement in collision responses for more natural blade motion.
  • Synchronized current and previous-frame displacement for more stable visuals and fewer artifacts.

• Chores

  • Updated Grass Collision version to 3.0.1.

[coderabbitai]

Walkthrough

Bump GrassCollision.ini version to 3-0-1 and modify GrassCollision.hlsli: adjust normal computation, introduce a distance-based nearFactor, replace fixed distance test with nearFactor > 0.0, clamp collision z components to non-positive values, and scale displacements by nearFactor while retaining the 0.75 multiplier.

Changes

Cohort / File(s)	Summary
Version bump (config) features/Grass Collision/Shaders/Features/GrassCollision.ini	Increment Info.Version from 3-0-0 to 3-0-1; no structural changes.
Shader collision & normal logic features/Grass Collision/Shaders/GrassCollision/GrassCollision.hlsli	Reworked ComputeNormalFromHeights to scale cross(tangentX,tangentY) by vec3(1.0,1.0,0.1) and return a safe normalized (or fallback) normal; introduced nearFactor = smoothstep(2048.0, 0.0, length(worldPosition)) and replaced fixed distance check with nearFactor > 0.0; clamp collision.z and previousCollision.z to -abs(z); multiply displacement and previousDisplacement by nearFactor while preserving the existing 0.75 multiplier; else branch unchanged (zero displacements).

Sequence Diagram(s)

sequenceDiagram
    autonumber
    participant Scene
    participant GrassShader as GrassCollision.hlsli
    participant GPU as Shader Output

    Scene->>GrassShader: worldPosition, height samples, collision inputs
    activate GrassShader

    GrassShader->>GrassShader: compute tangents & crossProd = cross(tangentX,tangentY) * vec3(1,1,0.1)
    GrassShader->>GrassShader: normalize crossProd (fallback to (0,0,-1) if tiny)
    GrassShader->>GrassShader: nearFactor = smoothstep(2048.0, 0.0, length(worldPosition))

    alt nearFactor > 0.0
        GrassShader->>GrassShader: clamp collision.z = -abs(collision.z)
        GrassShader->>GrassShader: clamp previousCollision.z = -abs(previousCollision.z)
        GrassShader->>GrassShader: displacement *= nearFactor * 0.75
        GrassShader->>GrassShader: previousDisplacement *= nearFactor * 0.75
        GrassShader->>GPU: output displaced position
    else
        GrassShader->>GPU: output original position (zero displacement)
    end
    deactivate GrassShader

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• chore(grass collision): less aggressive #1546: Modifies the same GrassCollision.hlsli functions (normal computation and displacement scaling); strong code overlap.
• feat(grass collision): implement with texture and history #1539: Edits collision sampling and normal-computation logic in GrassCollision.hlsli; closely related.
• chore(grass collision): simpler grass collision #1525: Adjusts collision/displacement handling in GrassCollision.hlsli; relevant to these edits.

Suggested reviewers

• jiayev

Poem

A rabbit hops through shader light,
Near steps hush the distant sight,
Normals shaped with a gentle bend,
Z tucked low where blades descend,
Version nudged — a quiet flight. 🐇🌿

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title “chore(grass collision): minor tweaks” succinctly conveys that the pull request makes small adjustments to the grass collision feature without unnecessary detail, aligning well with the actual changes to the shader and configuration files.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch grass-col-tweaks

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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.

[github-actions]

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

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (2)

features/Grass Collision/Shaders/GrassCollision/GrassCollision.hlsli (2)

99-102: Consider documenting the Z-axis dampening factor.

The float3(1.0, 1.0, 0.1) scaling applied to the cross product dampens the Z component by a factor of 10, making the resulting normal more horizontal. While this may be intentional for grass collision behavior (e.g., preferring horizontal displacement over vertical), a brief comment explaining the rationale would improve maintainability.

Example:

-		float3 crossProd = cross(tangentX, tangentY) * float3(1.0, 1.0, 0.1);
+		// Dampen Z component to favor horizontal collision normals over vertical
+		float3 crossProd = cross(tangentX, tangentY) * float3(1.0, 1.0, 0.1);

---

142-142: Use named constant instead of magic number.

The value 2048.0 is already defined as ZRANGE.x (line 20). Consider using the named constant for consistency and maintainability. If the constant values change in the future, this ensures the fade distance remains synchronized.

Apply this diff:

-		float nearFactor = smoothstep(2048.0, 0.0, length(worldPosition));
+		float nearFactor = smoothstep(ZRANGE.x, 0.0, length(worldPosition));

📜 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 9d165f3 and 2ba4cb9.

📒 Files selected for processing (1)

• features/Grass Collision/Shaders/GrassCollision/GrassCollision.hlsli (3 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:

• features/Grass Collision/Shaders/GrassCollision/GrassCollision.hlsli

features/*/Shaders/**/*.{hlsl,hlsli,fx,fxh}

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

features/*/Shaders/**/*.{hlsl,hlsli,fx,fxh}: Place all feature shaders under features/YourFeature/Shaders/
Avoid GPU register/buffer conflicts in HLSL; verify register usage (e.g., with hlslkit buffer scanning)

Files:

• features/Grass Collision/Shaders/GrassCollision/GrassCollision.hlsli

🔇 Additional comments (3)

features/Grass Collision/Shaders/GrassCollision/GrassCollision.hlsli (3)

144-144: LGTM: Smooth fade replaces hard cutoff.

The condition change from length(worldPosition) < 2048.0 to nearFactor > 0.0 is functionally correct and provides a smooth fade-out of collision effects, improving visual quality compared to the previous hard cutoff.

---

157-159: LGTM: Z-clamping prevents upward displacement.

The logic correctly ensures collision vectors only displace grass downward or sideways, not upward. The z = -abs(z) approach is efficient and the comment clearly explains the constraint.

---

164-165: LGTM: Distance-based fade improves performance and quality.

The addition of nearFactor to the displacement scaling provides a smooth distance-based fade-out of collision effects, which is good for both performance (reducing computation at far distances) and visual quality (avoiding abrupt cutoffs).

[alandtse]

@doodlum what's with the magic number 2048? The bot suggested a constant.

[doodlum]

@doodlum what's with the magic number 2048? The bot suggested a constant.

The array distance