AA Grass Pro v2.0

Scalable GPU-driven procedural foliage system for Unity. Paint anywhere on any collider mesh — featuring 3D V-keel blades, real-time shadow receiving, 4-tier continuous LOD blending, analytical multi-collider physics interaction, and dual-sided BSDF translucency.

URP & HDRP 3D V-Keel Geometry Shadow Receiving Analytical Physics Scalable GPU Instancing Unity 2022.3+ / Unity 6

🚀 What's New in Version 2.0

🌿

3D V-Shape Keel Blades

Replaced flat 2-vertex ribbon strips with 3-vertex V-creased cross-sections featuring a central spine keel and outward-flared cylindrical normals for realistic volumetric depth.

⚡

Dynamic Shadow Receiving

Directional sunlight and scene shadow casters are now received directly on grass blades in both HDRP and URP with automatic two-sided normal bias correction.

🔍

Auto-Detect & Attach Assets

Adding the Grass System component to any GameObject automatically discovers and links the required Compute Shader and Material assets without null references.

🌫️

Volumetric Fog Sync

Eliminated double-fog conflicts and horizontal slicing artifacts with synchronized depth prepasses, allowing HDRP atmospheric scattering to blend smoothly.

🎛️

Modernized GUI & Global Reset

Header features a top-right ↺ Reset All button with safety confirmation, per-section resets, styled subcards, and responsive master toggles.

📐

Analytical Multi-Collider Physics

True 64-byte GPU mathematical formulations for Spheres, Capsules, Oriented Boxes, and Wheels with elastic recovery and UV-shift tracking.

⚡ Quick Start

Create Grass System — Go to GameObject → AA Grass Pro → Create Grass System. Auto-creates system root, Wind Direction child, and auto-links compute shader + material.
Open Painter — Click 🎨 Open Painter in the Grass System Inspector or menu Window → AA Grass Pro → Grass Painter.
Paint — Left-click and drag across any surface with a Collider. A GrassRenderer is auto-spawned per unique surface.
Fine-Tune — Adjust Blade Geometry, 3-Tier Gradients, Wind, LOD Transition, and Physics in the modernized Inspector.

✅

No Unity Terrain required! Paint freely on static meshes, moving platforms, procedural geometry, or organic rocks.

🔧 Scene Setup

Scene Hierarchy Elements

Object	Purpose
`Grass System` (GameObject)	Root orchestrator holding global simulation settings. Exactly one per scene.
`Wind Direction` (child)	Rotate in the scene view to orient global wind wave propagation.
`GrassRenderer_{surface}`	Auto-attached child to painted surfaces. Holds GrassData + GPU compute buffers.
`GeneratedAssets/GrassMaterial.mat`	Universal instanced material configured for URP or HDRP.
`GeneratedAssets/GrassData_{surface}.asset`	ScriptableObject storing all serialized instances for persistence across sessions.

Platform & System Requirements

Requirement	Detail
Unity Version	2022.3 LTS, 2023.x, or Unity 6 (6000.x)
Render Pipelines	Universal Render Pipeline (URP) or High Definition Render Pipeline (HDRP)
Target Hardware	Compute Shader support (Shader Model 4.5+ / DX11 / DX12 / Vulkan / Metal)
Colliders	Standard Unity Collider attached to surfaces you wish to paint on

🎨 Painting Grass

Viewport Controls

Input	Action
Left-Click	Paint a single cluster at cursor position
Left-Click + Drag	Smooth continuous painting (throttled at ~30 ops/sec with 0.15m move delta)
Ctrl + Click / Drag	Instant eraser mode
Shift + Scroll	Dynamically adjust brush radius

Brush Properties

Setting	Range	Default	Description
Radius	0.1 – 20	2.0	Brush influence radius in world units
Density	1 – 100	15	Instances per stroke. Calculated as: `π × r² × density × 0.1`
Height Min / Max	0.2 – 2.0	0.7 – 1.3	Randomized vertical height scaling multiplier
Width Min / Max	0.2 – 2.0	0.7 – 1.3	Randomized horizontal blade width multiplier
Layers	LayerMask	Everything	Layers that the painting raycast recognizes

⚙️ Grass System & Modern GUI

The Inspector features high-visibility master toggle cards, a top-right ↺ Reset All button with safety confirmation dialog, individual section reset controls, and clean color palette subcards.

Inspector Toolbar & Header

Top-Right ↺ Reset All: Instantly resets all parameters back to factory defaults with an undo record and safety prompt.
🎨 Open Painter: Opens the brush tool window docked or floating.
🔄 Refresh All: Forces GPU indirect buffers and spatial chunks to rebuild across all active renderers.
Live Telemetry Card: Real-time counter of total Renderers, Instances, Spatial Chunks, and estimated GPU memory footprint.

🌿 3D V-Shape Keel Blades

Standard billboard ribbons appear paper-thin when viewed from angles. AA Grass Pro generates procedural 3D V-keel blades with true cross-sectional geometry:

3-Vertex Rows: Each height segment contains 3 vertices (Left Wing, Central Keel Spine, Right Wing).
Central Fold Crease: The central spine is indented inward along the Z-axis (-keelDepth), while outer wings flare outward.
Curvature Normals: Cylindrical outwards-angled normals (-0.75, 0.25, 0.62 and 0.75, 0.25, 0.62) create soft, natural specular highlights and diffuse wrap.

⚡ Shadow Receiving (HDRP & URP)

Grass blades receive direct sunlight shadows and scene shadows from characters, vehicles, and structures:

Feature	HDRP Implementation	URP Implementation
Sun Shadow Index	Resolves via `_DirectionalShadowIndex` dynamically	Samples Main Light shadow cascade attenuation
Two-Sided Normal Bias	Applies `FastSign(dot(N, L))` normal bias flip	Aligns bias with light direction on double-sided geometry
Inspector Control	`Receive Shadows` checkbox in Rendering & Shadows	`Receive Shadows` checkbox in Rendering & Shadows

📊 Hierarchical LOD & Blending

AA Grass Pro eliminates visible circular "pop" seams through a smooth 4-Tier Continuous LOD Pipeline.

LOD 0
0–30m (Full)

LOD 1
30–60m (70%)

LOD 2
60–90m (40%)

LOD 3 Quad
90m+ (20%)

Culled
> View Dist

Seamless Blending Mechanism

Continuous Density Ramp: Blades transitioning out dissolve smoothly into the ground rather than abruptly popping off.
Continuous Width Lerp: Surviving distant blades gradually widen to preserve visual screen coverage and foliage density.
Deterministic Hash: Every instance has a stable pseudo-random ID so density transitions remain 100% stable regardless of camera movement.

LOD Settings

Property	Range	Default	Description
Enable LOD	bool	true	Master toggle. When disabled, full LOD0 geometry renders at all distances.
Transition Range	1.0 – 20.0m	6.0m	Distance over which density dissolving and width scaling smoothly blend.
LOD Distance 1	5 – 100m	30m	Near-to-mid range threshold.
LOD Distance 2	20 – 200m	60m	Mid-to-far range threshold.
LOD Distance 3	30 – 300m	90m	Far-to-billboard quad threshold.
Density Reductions	0.0 – 0.95	0.3 / 0.6 / 0.8	Target cull fraction for each respective tier.

🤚 Physics & Interaction

The interaction subsystem runs entirely on the GPU, handling up to 32 simultaneous interactors with true analytical mathematical collision.

Collider Classification

Collider Type	GPU Representation	Interaction Behavior
Sphere	Center + Radius	Radial spherical displacement outward from impact center.
Capsule	Start + End Segment + Radius	Smooth cylindrical lateral displacement along character capsules.
Oriented Box	Center + Half-Extents + Forward	Directional flattening along moving vehicle chassis and boxes.
Wheel	Contact Patch + Radius	Aggressive tire compression track with high-friction push.

Interaction Properties

Property	Range	Default	Description
Enable Interaction	bool	true	Master switch for physics simulation.
Recovery Duration	0.05 – 5.0s	0.25s	Time in seconds for flattened grass blades to elastically spring back upright.
Push Strength	0.1 – 3.0	1.0	Max lateral displacement angle applied to pushed blades.
Height Threshold	0.0 – 2.0m	0.8m	Vertical cutoff preventing overhead objects from leaving ground trails.
Map Size	5 – 100m	30m	World-space footprint of the persistent interaction render texture around camera.
Map Resolution	64 – 2048	512	Render texture resolution for continuous footprint/tire stamping.
Interaction Layers	LayerMask	Everything	Physics layer mask filtering interactable scene colliders.

🌬️ Wind Simulation

Procedural noise-driven wind evaluated directly in the vertex stage without requiring scene WindZones.

Property	Range	Default	Description
Enable Wind	bool	true	Master toggle. Bypasses vertex wind displacement when disabled.
Direction Object	Transform	Wind Direction	Grass leans in this transform's forward vector direction.
Wind Strength	0.0 – 3.0	0.8	Base oscillation amplitude.
Wind Speed	0.0 – 8.0	2.0	Wave propagation velocity across the field.
Turbulence	0.0 – 2.0	0.4	High-frequency flutter added to blade tips.
Gust Strength & Freq	Various	0.25 / 0.8	Intermittent high-amplitude wind gusts sweeping across the scene.
Stiffness	0.0 – 1.0	0.6	Root rigidity preventing blades from detaching from ground.

💡 Lighting & 3-Color Gradients

3-Tier Vertical Color Gradient

Blades sample a continuous vertical gradient across their height:

Root Color: Dark ambient base anchoring the blade to the terrain surface.
Mid Color: Body foliage tone representing primary chlorophyll pigmentation.
Tip Color: Sun-lit, brighter blade tip capturing direct ambient illumination.

Lighting Properties

Property	Default	Description
Dual-Sided Translucency	Enabled (0.85)	Simulates sunlight transmitting through thin grass membrane.
Rim Lighting	Enabled (0.40)	Fresnel rim glow toward direct sunlight.
Specular Highlight	Disabled (0.15)	Blinn-Phong specular shimmer for wet or waxy vegetation.
Full Detail Distance	35m	Advanced lighting terms smoothly fade out past this distance to conserve fillrate.

🔷 URP Shader

Shader: AA Grass Pro/Grass URP. Passes: ForwardLit, ShadowCaster, DepthOnly.

Fully compatible with Universal Render Pipeline Forward and Forward+ rendering paths, screen-space ambient occlusion (SSAO), and soft cascaded shadows.

🔶 HDRP Shader & Volumetric Fog

Shader: AA Grass Pro/Grass HDRP. Passes: ForwardOnly, ShadowCaster, DepthForwardOnly.

Synchronized depth prepass ensures clean volumetric fog integration via HDRP's native OpaqueAtmosphericScattering pass.

💡

HDRP Fog Best Practice: In your Volume Profile's Fog component, set Base Height slightly below your terrain level and Maximum Height comfortably above grass blade tops. Set Slice Distribution Uniformity between 0.7 and 0.85 to prevent visible voxel slice stepping across dense vegetation fields.

⚡ Performance & Hardware Scalability

Indirect

GPU Draw Calls

68 B

GPU Instance Stride

64 B

Collider Data Stride

Dynamic

4-Tier LOD Scaling

ℹ️

Performance & Scalability Notice: Rendering performance, achievable instance counts, and framerates vary significantly based on your target hardware (GPU compute throughput, rasterization fillrate, VRAM bandwidth), screen resolution, active render pipeline (URP vs HDRP), shadow map distance, and scene lighting complexity. Rather than assuming static figures, tune the built-in Hierarchical LOD distance thresholds, density reduction ratios, blade segments, and view distance to achieve your desired performance profile on each target platform.

Hardware Scalability Guidelines

Hardware Profile	Suggested Density Spacing	View Distance	Shadow Distance	LOD Transition
High-End Desktop / Current-Gen Consoles	Dense (0.03m – 0.05m)	120m – 160m	50m – 80m	6m (Full 4-tier LOD)
Mid-Range Desktop / Steam Deck / Last-Gen	Balanced (0.05m – 0.08m)	80m – 100m	30m – 40m	8m (Aggressive LOD2/3 reduction)
Mobile / Handheld / Integrated GPUs	Optimized (0.08m – 0.12m)	50m – 70m	15m – 25m or Off	10m (High density reduction)

📘 Script API

GrassSystem API

Member	Type	Description
`GrassSystem.Instance`	static GrassSystem	Global singleton reference.
`ResetStyleSettings()`	void	Resets style palette to Realistic.
`ResetGeometrySettings()`	void	Resets blade segments, width, height, and curve.
`ResetColorSettings()`	void	Resets realistic/stylized colors, dry patches, and variation.
`ResetLightingSettings()`	void	Resets translucency, rim, specular, and curvature normals.
`ResetWindSettings()`	void	Resets procedural wind amplitude, speed, gusts, and stiffness.
`ResetRenderingSettings()`	void	Resets view distance, fade start, shadows, and frustum culling.
`ResetLODSettings()`	void	Resets LOD distances and tier reduction ratios.
`ResetInteractionSettings()`	void	Resets physics colliders, persistence, and resolution.
`ResetAllSettings()`	void	Resets all system settings back to factory defaults.
`AutoAssignReferences()`	void	Finds and binds compute shader and material assets (Editor).

GrassRenderer API

Member	Type	Description
`GrassDataAsset`	GrassData	ScriptableObject storing per-surface instances.
`InstanceCount`	int	Total number of grass instances on this surface.
`ChunkCount`	int	Number of active 20m spatial chunks built.
`AllRenderers`	static IReadOnlyList	All active renderers across the entire scene.
`UpdateBufferData()`	void	Lightweight GPU re-upload during realtime painting.
`RefreshData()`	void	Rebuilds spatial acceleration chunks and GPU indirect buffers.

📁 Package File Structure

Assets/AA_GrassPro/
├── package.json — Unity package manifest (v1.5.0)
├── README.md — Package documentation & setup guide
├── Editor/
│ ├── GrassGUI.cs — Modernized UI toolkit (master toggles, cards, badges, reset all)
│ ├── GrassPainter.cs — Scene-view brush tool with surface isolation
│ ├── GrassRendererEditor.cs — Custom Inspectors for GrassSystem & GrassRenderer
│ ├── GrassAutoSetup.cs — GameObject menu automated scene creator
│ └── AA.GrassPro.Editor.asmdef
├── Runtime/
│ ├── GrassSystem.cs — Main orchestrator, culling dispatch, material binder
│ ├── GrassRenderer.cs — Per-surface chunk manager & instanced indirect draw calls
│ ├── GrassData.cs — ScriptableObject instance storage & GPU structs
│ ├── GrassBladeMesh.cs — Procedural 3D V-keel mesh generator with curvature normals
│ ├── GrassInteractionMap.cs — Multi-collider buffer manager & UV-shifted trail RT
│ └── AA.GrassPro.Runtime.asmdef
├── Shaders/
│ ├── GrassCompute.compute — GPU culling, continuous LOD blend, analytical collision
│ ├── GrassProperties.hlsl — CBUFFER material and instancing declarations
│ ├── GrassLighting.hlsl — BSDF dual-sided translucency, shadow receiving, rim, curvature
│ ├── GrassCommon.hlsl — Vertex transforms, wind dynamics, quad billboard
│ ├── InteractionStamp.shader — Analytical collider footprint stamping
│ ├── InteractionFade.shader — UV-offset blit with exponential elastic recovery
│ ├── Grass.shader — Core multi-pipeline grass shader
│ ├── URP/
│ │ └── GrassURP.shader — Dedicated Universal Render Pipeline shader
│ └── HDRP/
│ └── GrassHDRP.shader — Dedicated High Definition Render Pipeline shader
└── Documentation/
└── index.html — Official package documentation

❓ FAQ & Troubleshooting

Q: Why does grass appear to dissolve smoothly instead of popping at distance?

This is the Continuous LOD transition blending. You can tune Transition Range in the Hierarchical LOD section if you want a tighter or broader transition zone.

Q: How do I test vehicle interaction with wheels?

Add colliders (such as WheelColliders, SphereColliders, or BoxColliders) to your vehicle. The GPU automatically detects their geometry type and applies directional push with elastic recovery.

Q: How do I prevent HDRP Volumetric Fog from creating harsh lines across the grass?

In your scene's Volume Profile, select the Fog component and set Base Height below the terrain and Maximum Height well above the grass. Increase Slice Distribution Uniformity to between 0.7 and 0.85 to smooth voxel slice transitions.

Q: Does my camera need to be tagged as MainCamera?

Tagging your active player/gameplay camera as MainCamera is recommended for standard Unity conventions. However, AA Grass Pro features an intelligent multi-fallback camera resolver that automatically detects active untagged cameras in the scene and seamlessly supports live Scene View inspection during Play Mode.

Q: How can I optimize performance on lower-spec devices?

Reduce View Distance (e.g. to 60m–80m), increase LOD tier density reductions (e.g. 0.4, 0.7, 0.85), set Blade Segments to 3 or 4, and limit or disable shadow distance on grass blades.

AA Grass Pro — Documentation v2.0 · Abyssal Ababeel