AMjHeightfieldActor

An actor that samples terrain height within its bounding box and registers

the result as a MuJoCo heightfield asset (mjsHField) into the shared mjSpec. Place this actor in the level over any landscape / static geometry. The Manager will auto-detect it during PreCompile() via a Cast and call Setup() to perform raycasting and spec population. A grid visualizer (ULineBatchComponent) is drawn in the editor viewport to preview the sample-point resolution. The grid refreshes automatically whenever any property is changed via the Details panel (driven by OnConstruction).

Attribute	Value
Kind	Class
UE Macro	UCLASS
Inherits	AActor

Properties Functions

Properties

Public Properties

Property	Type	Description
Resolution	int32	Number of sample points along each axis (Resolution x Resolution grid).
HFieldName	FString	Name used to register the heightfield asset in the MuJoCo spec.
ElevationTraceChannel	TEnumAsByte<ECollisionChannel>	Collision channel to use for downward height raycasts.
bForceRecache	bool	Force re-sampling on next compile, ignoring any cached heightfield data.
TraceWhitelist	TArray<TSoftObjectPtr<AActor>>	Whitelist of actors to trace against for height sampling.
BaseThickness	float	Thickness of the solid base below the heightfield surface, expressed
bShowGrid	bool	If true, a grid preview is rendered in the editor viewport.
GridColor	FLinearColor	Color used to draw the resolution grid lines.
BoundsBox	UBoxComponent*	Root box component — defines the sampling region. Scale/move this in the editor.
GridLines	ULineBatchComponent*	Line batch used to draw the resolution grid in the editor.

Resolution

Number of sample points along each axis (Resolution x Resolution grid).

• Type: int32
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield

HFieldName

Name used to register the heightfield asset in the MuJoCo spec.

• Type: FString
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield

ElevationTraceChannel

Collision channel to use for downward height raycasts.

• Type: TEnumAsByte
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield

bForceRecache

Force re-sampling on next compile, ignoring any cached heightfield data.

• Type: bool
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield

TraceWhitelist

Whitelist of actors to trace against for height sampling.

• Type: TArray>
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield

BaseThickness

Thickness of the solid base below the heightfield surface, expressed

• Type: float
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield

bShowGrid

If true, a grid preview is rendered in the editor viewport.

• Type: bool
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield|Visualizer

GridColor

Color used to draw the resolution grid lines.

• Type: FLinearColor
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Heightfield|Visualizer

BoundsBox

Root box component — defines the sampling region. Scale/move this in the editor.

• Type: UBoxComponent*
• Editor: 👁 VisibleAnywhere
• Blueprint: 🟢 ReadOnly
• Category: MuJoCo|Heightfield

GridLines

Line batch used to draw the resolution grid in the editor.

• Type: ULineBatchComponent*
• Editor: 👁 VisibleAnywhere
• Blueprint: 🟢 ReadOnly
• Category: MuJoCo|Heightfield|Visualizer

Functions

Public Functions

General

Function	Returns	Description
Setup()	void	Called by AMuJoCoManager::PreCompile(). Raycasts the terrain under the
PostSetup()	void	Called by AMuJoCoManager::PostCompile(). Currently a no-op for static terrain.

Setup

Called by AMuJoCoManager::PreCompile(). Raycasts the terrain under the

• Signature: Setup(mjSpec* Spec, mjVFS* VFS)

PostSetup

Called by AMuJoCoManager::PostCompile(). Currently a no-op for static terrain.

• Signature: PostSetup(mjModel* Model, mjData* Data)

Protected Functions

General

Function	Returns	Description
OnConstruction()	void	Called when the actor is constructed or a property changes in the editor.

OnConstruction

Called when the actor is constructed or a property changes in the editor.

• Signature: OnConstruction(const FTransform& Transform)

Private Functions

General

Function	Returns	Description
RebuildGridVisualizer()	void	Rebuilds the GridLines component to reflect the current Resolution and bounds.
SampleHeightAt()	float	Traces downward to find the terrain height, ignoring MuJoCo actors.
GetCacheFilePath()	FString	Returns the cache file path for this heightfield.
ComputeCacheKey()	FString	Computes a cache key from actor transform, resolution, and bounds.
SaveCache()	bool	Saves sampled heightfield data to a binary cache file.
LoadCache()	bool	Loads cached heightfield data. Returns true if cache is valid.

RebuildGridVisualizer

Rebuilds the GridLines component to reflect the current Resolution and bounds.

• Signature: RebuildGridVisualizer()

SampleHeightAt

Traces downward to find the terrain height, ignoring MuJoCo actors.

• Signature: SampleHeightAt(const FVector2D& WorldXY, const FBox& Bounds)
• Returns: float

GetCacheFilePath

Returns the cache file path for this heightfield.

• Signature: GetCacheFilePath()
• Returns: FString

ComputeCacheKey

Computes a cache key from actor transform, resolution, and bounds.

• Signature: ComputeCacheKey()
• Returns: FString

SaveCache

Saves sampled heightfield data to a binary cache file.

• Signature: SaveCache(const TArray<float>& NormHeights, float MinH, float ElevRange, const FBox& Bounds, const FString& CacheKey)
• Returns: bool

LoadCache

Loads cached heightfield data. Returns true if cache is valid.

• Signature: LoadCache(TArray<float>& OutNormHeights, float& OutMinH, float& OutElevRange, FBox& OutBounds, const FString& ExpectedCacheKey)
• Returns: bool