Ground Materials

RCCP uses PhysicMaterial-based surface detection to vary friction, particles, sounds, and skidmarks depending on what surface the wheels are touching. Every ground collider in your scene can be mapped to a set of surface properties, and Unity Terrains are supported through splatmap-based detection.

For general project setup, see Installation. For vehicle configuration, see Vehicle Setup.

Overview

The ground materials system works as follows:

Each wheel checks which PhysicMaterial is on the collider it is touching.
The system looks up that PhysicMaterial in the RCCP_GroundMaterials asset.
If a match is found, the corresponding friction, particle, sound, and skidmark settings are applied to that wheel.
For Unity Terrains, the system reads the splatmap to determine which terrain texture has the highest weight at the wheel's position, then maps that texture to a PhysicMaterial.

RCCP_GroundMaterials ScriptableObject

RCCP_GroundMaterials is a singleton ScriptableObject loaded from the Resources folder. Access it at runtime via:


RCCP_GroundMaterials groundMats = RCCP_GroundMaterials.Instance;

The asset is located at:


Assets/Realistic Car Controller Pro/Resources/RCCP_GroundMaterials.asset

It contains two main arrays:

Array	Type	Purpose
`frictions`	`GroundMaterialFrictions[]`	Per-surface settings for regular colliders
`terrainFrictions`	`TerrainFrictions[]`	Splatmap-to-PhysicMaterial mappings for terrains

GroundMaterialFrictions

Each entry in the frictions array defines how a specific surface type behaves. Here are all the fields:

Field	Type	Default	Description
`groundMaterial`	`PhysicsMaterial`	(none)	The Unity physics material assigned to ground colliders. This is the key used for surface matching.
`forwardStiffness`	`float`	1	Affects braking and acceleration grip. Higher values mean more grip along the wheel's forward axis.
`sidewaysStiffness`	`float`	1	Affects cornering grip. Higher values mean less lateral sliding.
`slip`	`float`	0.25	Slip threshold before particles and skidmarks begin to appear. Lower values make effects trigger sooner.
`damp`	`float`	1	Damping force applied to the wheel on this surface.
`volume`	`float`	1	Volume of the tire-on-surface sound (range 0 to 1).
`groundParticles`	`GameObject`	(none)	Particle prefab to spawn when the wheel slips on this surface (dust, gravel, snow, etc.). Must have or will receive an `RCCP_WheelSlipParticles` component.
`groundSound`	`AudioClip`	(none)	Audio clip played when the wheel rolls on this surface.
`skidmark`	`RCCP_Skidmarks`	(none)	Skidmark prefab used to draw tire marks on this surface.

Note on PhysicsMaterial vs PhysicMaterial: In Unity 2023.3 and newer (including Unity 6), the type is PhysicsMaterial. In older versions, it is PhysicMaterial. RCCP handles this automatically with preprocessor directives.

Example Configurations

Surface	forwardStiffness	sidewaysStiffness	slip	damp	Particles	Sound
Asphalt	1.0	1.0	0.25	1.0	None or light smoke	Tire hum
Gravel	0.7	0.7	0.15	0.8	Gravel dust	Crunching gravel
Grass	0.5	0.5	0.1	0.6	Grass/dirt particles	Soft rolling
Sand	0.4	0.4	0.1	0.5	Sand spray	Sand whoosh
Ice	0.15	0.15	0.05	0.3	None	Ice scrape

Setting Up a New Surface

Follow these steps to add a new ground surface type:

Step 1: Create a PhysicMaterial

In the Unity Project window, right-click and select Create > Physic Material (or Physics Material in Unity 6).
Name it descriptively (for example, PM_Gravel).
Configure its friction and bounciness values as needed.

Step 2: Assign It to Your Ground Collider

Select the ground GameObject in your scene (a MeshCollider, BoxCollider, etc.).
In the Inspector, find the collider component.
Drag your new PhysicMaterial into the Material field of the collider.

Step 3: Open the Ground Materials Asset

Navigate to Assets/Realistic Car Controller Pro/Resources/.
Select RCCP_GroundMaterials.asset.
Alternatively, open it from the menu: Tools > BoneCracker Games > Realistic Car Controller Pro > Configuration > Ground Physics Materials.

Step 4: Add a New Friction Entry

In the Inspector for RCCP_GroundMaterials, find the Frictions array.
Increase the array size by 1.
In the new entry, assign your PhysicMaterial to the groundMaterial field.

Step 5: Configure the Entry

Set forwardStiffness and sidewaysStiffness to control grip.
Adjust slip to control when visual effects begin.
Set damp for the surface damping.
Assign a particle prefab to groundParticles (optional).
Assign an audio clip to groundSound (optional).
Assign a skidmark prefab to skidmark (optional).

Step 6: Validate Particle Prefabs

RCCP_GroundMaterials includes a CheckWheelPrefabsForMissingScript() method that ensures all assigned particle prefabs have the required RCCP_WheelSlipParticles component. This is called automatically, but you can trigger it manually if needed.

Terrain Support

RCCP supports Unity Terrains through splatmap-based surface detection. Instead of using a single PhysicMaterial for the entire terrain, the system checks which terrain texture (layer) has the highest weight at each wheel's position and maps it to the corresponding ground material.

How It Works

On scene start, RCCP_SceneManager calls GetAllTerrains() to find and cache all Terrain.activeTerrains.
For each terrain, the following data is cached in a Terrains class:

Field	Description
`terrain`	Reference to the Unity Terrain component
`mTerrainData`	Cached `TerrainData` for alphamap access
`terrainCollider`	PhysicMaterial from the terrain's `TerrainCollider`
`alphamapWidth`	Width of the terrain alphamap in pixels
`alphamapHeight`	Height of the terrain alphamap in pixels
`mSplatmapData`	Full alphamap array `[x, y, textureIndex]`
`mNumTextures`	Number of terrain texture layers

At runtime, each wheel that detects it is on a terrain surface reads the cached splatmap data to find which texture has the highest weight at its world position.
The TerrainFrictions entries in RCCP_GroundMaterials map terrain layer indexes to PhysicMaterials.

TerrainFrictions Configuration

The terrainFrictions array in RCCP_GroundMaterials contains entries with:

Field	Type	Description
`groundMaterial`	`PhysicsMaterial`	The PhysicMaterial that this terrain layer maps to. Must match an entry in the `frictions` array.
`splatmapIndexes`	`SplatmapIndexes[]`	Array of terrain texture layer indexes that use this PhysicMaterial.

Each SplatmapIndexes entry has a single field:

Field	Type	Description
`index`	`int`	The terrain layer index (starting at 0) in the terrain's texture list.

Setting Up Terrain Surfaces

Open RCCP_GroundMaterials.asset.
In the Terrain Frictions array, add one entry per surface type present on your terrain.
For each entry:

Assign the groundMaterial to the PhysicMaterial that also exists in your frictions array.
Add the splatmap layer indexes that correspond to this surface type. For example, if your terrain's first texture (index 0) is grass, set index = 0.

Make sure the PhysicMaterial on the TerrainCollider is also present in the frictions array as a fallback.

Example

Suppose your terrain has three layers:

Layer Index	Texture	Desired Surface
0	Grass	Grass (low grip)
1	Dirt Path	Gravel (medium grip)
2	Rock	Asphalt (high grip)

You would create three terrainFrictions entries, each pointing to the appropriate PhysicMaterial (which must also have a matching entry in the frictions array with particles, sounds, and skidmarks configured).

Skidmarks System

Skidmarks are the tire marks left on the ground when wheels slip. RCCP uses a shared manager to handle all skidmark rendering.

Architecture

Component	Role
`RCCP_SkidmarksManager`	Singleton manager. Creates one `RCCP_Skidmarks` instance per ground material at scene start. Routes wheel slip data to the correct skidmark instance.
`RCCP_Skidmarks`	The actual skidmark renderer. Uses a ring buffer of `MarkSection` entries and dynamically builds a mesh. Supports both multithreaded and single-threaded mesh generation.

How Skidmarks Are Generated

RCCP_SkidmarksManager instantiates one RCCP_Skidmarks prefab per entry in the frictions array on Awake.
When a wheel slips, it calls RCCP_SkidmarksManager.Instance.AddSkidMark() with:

pos -- world position of the mark
normal -- surface normal
intensity -- opacity from 0 (transparent) to 1 (fully visible)
width -- width in meters
lastIndex -- index of the previous section (-1 for a new strip)
groundIndex -- which ground material the wheel is on

The skidmark prefab builds quad strips from connected sections, stored in a ring buffer with a maximum of maxMarks sections (default 1024).

Skidmark Prefab Settings

Each RCCP_Skidmarks prefab on the skidmark GameObject has:

Property	Default	Description
`maxMarks`	1024	Maximum number of mark sections before the ring buffer wraps
`groundOffset`	0.02	Height above the surface in meters to prevent z-fighting
`minDistance`	0.04	Minimum distance between consecutive sections. Closer sections are skipped.

Cleaning Skidmarks at Runtime


// Clean all skidmarks in the scene
RCCP.CleanSkidmarks();

// Clean skidmarks for a specific ground material index
RCCP.CleanSkidmarks(0); // Cleans skidmarks for the first ground material

These methods call through to RCCP_SkidmarksManager.Instance.CleanSkidmarks(), which resets the mark counter and triggers a mesh rebuild.

Performance Notes

RCCP_Skidmarks supports multithreaded mesh generation when RCCP_SceneManager.multithreadingSupported is true. The vertex, normal, UV, color, and triangle arrays are built on a background thread, then applied to the mesh on the main thread.
If multithreading is not supported, the DrawRaw() fallback builds the mesh synchronously.
The ring buffer design (maxMarks) means old skidmarks are automatically overwritten, preventing unlimited memory growth.

Common Issues

No Skidmarks on a Surface

Verify that the skidmark field is assigned in the matching GroundMaterialFrictions entry.
Confirm that the slip threshold is not set too high. If slip is very large, the wheel may never exceed it.
Check that the RCCP_SkidmarksManager singleton is present in the scene. It is created automatically, but verify it exists under DontDestroyOnLoad.

Wrong Particles or Sounds on a Surface

The most common cause is a mismatch between the PhysicMaterial on the collider and the one in the frictions array. Select the ground collider and verify its Material field matches the groundMaterial in the corresponding friction entry.
If you duplicated a collider, the PhysicMaterial reference may have been lost. Reassign it.

Terrain Surface Not Detected

RCCP_SceneManager caches terrain data on Awake. If the terrain is instantiated or enabled after the scene starts, the cache will be empty. Make sure all terrains are active before play mode begins.
Verify that the terrain layer indexes in terrainFrictions[].splatmapIndexes match the actual layer order in your Terrain's texture list.
Check that RCCP_SceneManager.Instance.terrainsInitialized is true at runtime.

Particles Do Not Appear

Ensure the groundParticles prefab is assigned in the friction entry.
The prefab must have or will automatically receive an RCCP_WheelSlipParticles component. If the prefab is missing a ParticleSystem, no particles will be visible.
Check that the particle prefab's emission settings and lifetime are configured to actually produce visible particles.

Skidmarks Flicker or Z-Fight

Increase the groundOffset value on the RCCP_Skidmarks prefab. The default of 0.02 meters works for most surfaces, but very uneven terrain may need a higher value.