fix(import): geom default resolution, GLB normals, degenerate-transform guards

Scripts/clean_meshes.py

@@ -54,9 +54,18 @@ def clean_mesh(mesh):
  mesh.remove_unreferenced_vertices()
  try:
  import networkx # noqa: F401 - trimesh's fix_normals requires it
- mesh.fix_normals()
  except ImportError:
- print(" Warning: networkx not installed, skipping fix_normals (GLB may have lighting issues)")
+ # A GLB exported without fixed normals imports into Unreal with
+ # degenerate normals/tangents on every mesh. Failing here makes
+ # convert_mesh() skip the GLB entirely, so the importer falls back
+ # to the source mesh and Unreal computes clean normals itself.
+ raise RuntimeError(
+ "networkx is not installed (required by trimesh.fix_normals); "
+ "skipping GLB conversion so the source mesh is imported instead. "
+ "Install it via the plugin's Python-dependency prompt or "
+ "'python -m pip install networkx'."
+ )
+ mesh.fix_normals()
 
  # Rotate -90 degrees around X for GLTF Y-up -> Unreal Z-up
  rotation_matrix = trimesh.transformations.rotation_matrix(-np.radians(90), [1, 0, 0])
@@ -66,6 +75,19 @@ def clean_mesh(mesh):
  return mesh
 
 
+_SCRIPT_MTIME = Path(__file__).stat().st_mtime
+
+
+def glb_up_to_date(output_glb: Path, source_path: Path) -> bool:
+ """A GLB is stale when older than its source mesh OR older than this
+ script -- conversion fixes ship with the script, so GLBs produced by an
+ older version must be regenerated."""
+ if not output_glb.exists():
+ return False
+ mtime = output_glb.stat().st_mtime
+ return mtime > source_path.stat().st_mtime and mtime > _SCRIPT_MTIME
+
+
 def convert_mesh(input_path: Path, output_path: Path) -> bool:
  """Convert a single mesh file to GLB."""
  print(f"\n Converting: {input_path.name} -> {output_path.name}")
@@ -99,7 +121,10 @@ def convert_mesh(input_path: Path, output_path: Path) -> bool:
  if np.allclose(size, 0):
  print(f" Warning: Mesh has zero size!")
 
- cleaned_mesh.export(str(output_path))
+ # include_normals: trimesh omits the NORMAL accessor by default and
+ # Unreal then builds the mesh with zero normals ("degenerate tangent
+ # bases" / "nearly zero normals" on every import).
+ cleaned_mesh.export(str(output_path), include_normals=True)
  print(f" -> Saved: {output_path.name}")
  return True
 
@@ -346,9 +371,11 @@ def process_xml(xml_path: Path):
  source_path = mesh_base / file_attr
  if source_path.exists():
  output_glb = source_path.with_suffix(".glb")
- if not output_glb.exists() or output_glb.stat().st_mtime < source_path.stat().st_mtime:
+ if not glb_up_to_date(output_glb, source_path):
  print(f"\n[flexcomp] Converting mesh: {source_path.name} -> {output_glb.name}")
- convert_mesh(source_path, output_glb)
+ if not convert_mesh(source_path, output_glb) and output_glb.exists():
+ output_glb.unlink()
+ print(f"[flexcomp] Removed stale GLB: {output_glb.name}")
  else:
  print(f"\n[flexcomp] Mesh up to date: {output_glb.name}")
 
@@ -446,8 +473,7 @@ def process_xml(xml_path: Path):
  print(f"\n x Source not found: {actual_source}")
  continue
 
- # Skip if GLB already exists and is newer than source
- if output_glb.exists() and output_glb.stat().st_mtime > actual_source.stat().st_mtime:
+ if glb_up_to_date(output_glb, actual_source):
  print(f"\n Skipping '{mesh_name}' (GLB up to date): {output_glb.name}")
  success_count += 1
  continue
@@ -457,6 +483,13 @@ def process_xml(xml_path: Path):
  success_count += 1
  else:
  print(f" x FAILED to convert {actual_source.name}")
+ # Never leave a stale or partial GLB behind: the importer
+ # prefers .glb over the source mesh, so a leftover here would
+ # silently ship the very data the conversion just refused to
+ # produce.
+ if output_glb.exists():
+ output_glb.unlink()
+ print(f" -> Removed stale GLB: {output_glb.name}")
 
  # Phase 4: Write updated XML
  output_xml = xml_path.parent / f"{xml_path.stem}_ue.xml"

Source/URLab/Private/MuJoCo/Components/Bodies/MjBody.cpp

@@ -121,6 +121,27 @@ void UMjBody::ApplyRenderState(const FMjRenderSnapshot& Snap)
 	const FVector MuJoCoWorldPos = MjUtils::MjToUEPosition(&Snap.XPos[PosIdx]);
 	const FQuat MuJoCoWorldQuat = MjUtils::MjToUERotation(&Snap.XQuat[QuatIdx]);
 
+	// A zero or non-finite snapshot row would write a degenerate transform
+	// that NaN-floods the renderer (NIL LocalToWorld in the distance-field
+	// pass) for every mesh under this body. Skip the frame and name the
+	// offender once.
+	if (MuJoCoWorldPos.ContainsNaN() || MuJoCoWorldQuat.ContainsNaN()
+ || MuJoCoWorldQuat.SizeSquared() < KINDA_SMALL_NUMBER)
+	{
+ if (!m_bWarnedDegenerateXform)
+ {
+ UE_LOG(LogURLabBind, Warning,
+ TEXT("MjBody::ApplyRenderState - Body '%s' (id=%d) got a "
+ "degenerate snapshot transform (pos=%s quat=[%f %f %f %f]); "
+ "skipping."),
+ *GetName(), Id, *MuJoCoWorldPos.ToString(),
+ Snap.XQuat[QuatIdx], Snap.XQuat[QuatIdx + 1],
+ Snap.XQuat[QuatIdx + 2], Snap.XQuat[QuatIdx + 3]);
+ m_bWarnedDegenerateXform = true;
+ }
+ return;
+	}
+
 	FVector CorrectedPos = MuJoCoWorldPos;
 
 	if (bIsQuickConverted)

Source/URLab/Private/MuJoCo/Components/Geometry/MjGeom.cpp

@@ -488,6 +488,25 @@ void UMjGeom::UpdateGlobalTransform()
  mju_mat2Quat(quat, const_cast<mjtNum*>(&Snap.GeomXMat[MatIdx]));
  const FQuat WorldRot = MjUtils::MjToUERotation(quat);
 
+ // A zero or non-finite snapshot row would write a degenerate
+ // transform that NaN-floods the renderer (NIL LocalToWorld in the
+ // distance-field pass). Skip the frame and name the offender once.
+ if (WorldPos.ContainsNaN() || WorldRot.ContainsNaN()
+ || WorldRot.SizeSquared() < KINDA_SMALL_NUMBER)
+ {
+ if (!m_bWarnedDegenerateXform)
+ {
+ UE_LOG(LogURLabBind, Warning,
+ TEXT("MjGeom::UpdateGlobalTransform - geom '%s' (id=%d) got a "
+ "degenerate snapshot transform (pos=%s quat=[%f %f %f %f]); "
+ "skipping."),
+ *GetName(), Id, *WorldPos.ToString(),
+ quat[0], quat[1], quat[2], quat[3]);
+ m_bWarnedDegenerateXform = true;
+ }
+ return;
+ }
+
  SetWorldLocation(WorldPos);
  SetWorldRotation(WorldRot);
 	});

Source/URLab/Private/MuJoCo/Components/Geometry/Primitives/MjBox.cpp

@@ -96,17 +96,30 @@ void UMjBox::ImportFromXml(const FXmlNode* Node, const FMjCompilerSettings& Comp
 	// --- CODEGEN_IMPORT_END ---
 
 	Super::ImportFromXml(Node, CompilerSettings);
-	// MuJoCo box size is 3 half-extents in metres.
-	Extents = FVector(
- size.Num() > 0 ? size[0] : 0.0f,
- size.Num() > 1 ? size[1] : 0.0f,
- size.Num() > 2 ? size[2] : 0.0f);
+	SyncEditorScaleFromSize();
+}
+
+void UMjBox::SyncEditorScaleFromSize()
+{
+	// MuJoCo box size is 3 half-extents in metres. Sentinel -1 marks a slot
+	// the fromto canon left unset; treat it like a missing slot.
+	auto ReadSlot = [this](int32 i) -> float {
+ if (size.Num() <= i)
+ return 0.0f;
+ return size[i] < 0.0f ? 0.0f : size[i];
+	};
+	Extents = FVector(ReadSlot(0), ReadSlot(1), ReadSlot(2));
+
+	if (Extents.GetMin() <= 0.0f)
+	{
+ // Size not resolvable yet (inherited from a default class); keep the
+ // current scale rather than baking a degenerate zero into the template.
+ return;
+	}
 
-	// Sync Unreal scale immediately on import so the editor visual matches the data
 	const float BaseSize = 50.0f;
 	const float UnitScale = 100.0f;
-	FVector NewScale = (Extents * UnitScale) / BaseSize;
-	SetRelativeScale3D(NewScale);
+	SetRelativeScale3D((Extents * UnitScale) / BaseSize);
 }
 
 void UMjBox::ExportTo(mjsGeom* Element, mjsDefault* def)

Source/URLab/Private/MuJoCo/Components/Geometry/Primitives/MjCapsule.cpp

@@ -140,7 +140,11 @@ void UMjCapsule::ImportFromXml(const FXmlNode* Node, const FMjCompilerSettings&
 	// --- CODEGEN_IMPORT_END ---
 
 	Super::ImportFromXml(Node, CompilerSettings);
+	SyncEditorScaleFromSize();
+}
 
+void UMjCapsule::SyncEditorScaleFromSize()
+{
 	// Super already resolves any `fromto` into pos/quat + size[1] (half-length).
 	// Capsule's MJCF `size` is [radius, halflength] — same layout as cylinder.
 	// The codegen fromto canon writes -1.0f sentinels for slots not set
@@ -153,6 +157,13 @@ void UMjCapsule::ImportFromXml(const FXmlNode* Node, const FMjCompilerSettings&
 	Radius = ReadSlot(0);
 	HalfLength = ReadSlot(1);
 
+	if (Radius <= 0.0f || HalfLength <= 0.0f)
+	{
+ // Size not resolvable yet (inherited from a default class); keep the
+ // current scale rather than baking a degenerate zero into the template.
+ return;
+	}
+
 	// Map (radius, halflength) → parent scale, mirroring UMjCylinder.
 	FVector NewScale;
 	NewScale.X = NewScale.Y = (Radius * kCmPerM) / kBaseHalf;

Source/URLab/Private/MuJoCo/Components/Geometry/Primitives/MjCylinder.cpp

@@ -80,6 +80,11 @@ void UMjCylinder::ImportFromXml(const FXmlNode* Node, const FMjCompilerSettings&
 	// --- CODEGEN_IMPORT_END ---
 
 	Super::ImportFromXml(Node, CompilerSettings);
+	SyncEditorScaleFromSize();
+}
+
+void UMjCylinder::SyncEditorScaleFromSize()
+{
 	// Clamp -1.0f sentinels (set by the fromto canon when slot is unset).
 	auto ReadSlot = [this](int32 i) -> float {
  if (size.Num() <= i)
@@ -89,7 +94,13 @@ void UMjCylinder::ImportFromXml(const FXmlNode* Node, const FMjCompilerSettings&
 	Radius = ReadSlot(0);
 	HalfLength = ReadSlot(1);
 
-	// Sync Unreal scale immediately on import so the editor visual matches the data
+	if (Radius <= 0.0f || HalfLength <= 0.0f)
+	{
+ // Size not resolvable yet (inherited from a default class); keep the
+ // current scale rather than baking a degenerate zero into the template.
+ return;
+	}
+
 	const float BaseSize = 50.0f;
 	const float UnitScale = 100.0f;
 	FVector NewScale;

Source/URLab/Private/MuJoCo/Components/Geometry/Primitives/MjSphere.cpp

@@ -80,13 +80,22 @@ void UMjSphere::ImportFromXml(const FXmlNode* Node, const FMjCompilerSettings& C
 	// --- CODEGEN_IMPORT_END ---
 
 	Super::ImportFromXml(Node, CompilerSettings);
-	Radius = size.Num() > 0 ? size[0] : 0.0f;
+	SyncEditorScaleFromSize();
+}
+
+void UMjSphere::SyncEditorScaleFromSize()
+{
+	Radius = size.Num() > 0 ? FMath::Max(size[0], 0.0f) : 0.0f;
+	if (Radius <= 0.0f)
+	{
+ // Size not resolvable yet (inherited from a default class); keep the
+ // current scale rather than baking a degenerate zero into the template.
+ return;
+	}
 
-	// Sync Unreal scale immediately on import so the editor visual matches the data
 	const float BaseSize = 50.0f;
 	const float UnitScale = 100.0f;
-	FVector NewScale = FVector((Radius * UnitScale) / BaseSize);
-	SetRelativeScale3D(NewScale);
+	SetRelativeScale3D(FVector((Radius * UnitScale) / BaseSize));
 }
 
 void UMjSphere::ExportTo(mjsGeom* Element, mjsDefault* def)

Source/URLab/Private/MuJoCo/Components/QuickConvert/MjQuickConvertComponent.cpp

@@ -363,6 +363,14 @@ void UMjQuickConvertComponent::ApplyRenderState(const FMjRenderSnapshot& Snap)
 	const FVector Pos = MjUtils::MjToUEPosition(&Snap.XPos[PosIdx]);
 	const FQuat Quat = MjUtils::MjToUERotation(&Snap.XQuat[QuatIdx]);
 
+	// Mirror UMjBody::ApplyRenderState: never apply a zero/NaN snapshot row --
+	// it writes a degenerate transform that NaN-floods the renderer.
+	if (Pos.ContainsNaN() || Quat.ContainsNaN()
+ || Quat.SizeSquared() < KINDA_SMALL_NUMBER)
+	{
+ return;
+	}
+
 	m_actor->SetActorRotation(Quat);
 	m_actor->SetActorLocation(Pos);
 }

Source/URLab/Public/MuJoCo/Components/Bodies/MjBody.h

@@ -221,6 +221,10 @@ class URLAB_API UMjBody : public UMjComponent
 
 	bool m_IsSetup = false;
 
+	// One-shot guard so a degenerate (zero/NaN) snapshot transform warns once
+	// instead of every frame.
+	bool m_bWarnedDegenerateXform = false;
+
 	FVector m_MeshPivotOffset = FVector::ZeroVector;
 
 	UPROPERTY()

Source/URLab/Public/MuJoCo/Components/Geometry/MjGeom.h

@@ -214,6 +214,15 @@ class URLAB_API UMjGeom : public UMjComponent
  */
 	virtual void SyncUnrealTransformFromMj();
 
+	/**
+ * @brief Recomputes the editor-preview RelativeScale3D from `size`.
+ * No-op when the needed size slots are missing or non-positive, so a geom
+ * whose size is inherited from a default class keeps its current scale
+ * instead of collapsing to zero. Primitive subclasses override this with
+ * their size-to-scale mapping.
+ */
+	virtual void SyncEditorScaleFromSize() {}
+
 	/** @brief Sets visibility for this geom and its child visual components. */
 	virtual void SetGeomVisibility(bool bNewVisibility);
 
@@ -299,6 +308,10 @@ class URLAB_API UMjGeom : public UMjComponent
 	UPROPERTY()
 	bool bWasImported = false;
 
+	/** One-shot guard so a degenerate snapshot transform warns once per geom
+ * instead of every frame. */
+	bool m_bWarnedDegenerateXform = false;
+
 	/** @brief Name of the mesh asset if Type is mesh. */
 	UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "MuJoCo|Geom")
 	FString MeshName;

Source/URLab/Public/MuJoCo/Components/Geometry/Primitives/MjBox.h

@@ -55,6 +55,8 @@ class URLAB_API UMjBox : public UMjGeom
 	virtual void ExportTo(mjsGeom* Element, mjsDefault* def = nullptr) override;
 
 	virtual void SyncUnrealTransformFromMj() override;
+
+	virtual void SyncEditorScaleFromSize() override;
 	virtual void SetGeomVisibility(bool bNewVisibility) override;
 
 	virtual class UStaticMeshComponent* GetVisualizerMesh() const override

Source/URLab/Public/MuJoCo/Components/Geometry/Primitives/MjCapsule.h

@@ -84,6 +84,8 @@ class URLAB_API UMjCapsule : public UMjGeom
 	virtual void ExportTo(mjsGeom* Element, mjsDefault* def = nullptr) override;
 
 	virtual void SyncUnrealTransformFromMj() override;
+
+	virtual void SyncEditorScaleFromSize() override;
 	virtual void SetGeomVisibility(bool bNewVisibility) override;
 
 #if WITH_EDITOR

Source/URLab/Public/MuJoCo/Components/Geometry/Primitives/MjCylinder.h

@@ -59,6 +59,8 @@ class URLAB_API UMjCylinder : public UMjGeom
 	virtual void ExportTo(mjsGeom* Element, mjsDefault* def = nullptr) override;
 
 	virtual void SyncUnrealTransformFromMj() override;
+
+	virtual void SyncEditorScaleFromSize() override;
 	virtual void SetGeomVisibility(bool bNewVisibility) override;
 
 #if WITH_EDITOR

Source/URLab/Public/MuJoCo/Components/Geometry/Primitives/MjSphere.h

@@ -55,6 +55,8 @@ class URLAB_API UMjSphere : public UMjGeom
 	virtual void ExportTo(mjsGeom* Element, mjsDefault* def = nullptr) override;
 
 	virtual void SyncUnrealTransformFromMj() override;
+
+	virtual void SyncEditorScaleFromSize() override;
 	virtual void SetGeomVisibility(bool bNewVisibility) override;
 
 #if WITH_EDITOR