This LOD heuristic selects LOD children on the basis of distance from the view point to the LOD root. More...

#include <distanceHeuristic.h>

Inheritance diagram for UsdLodDistanceHeuristic:

Public Member Functions
	UsdLodDistanceHeuristic (const UsdPrim &prim=UsdPrim())
	Construct a UsdLodDistanceHeuristic on UsdPrim `prim` .

	UsdLodDistanceHeuristic (const UsdSchemaBase &schemaObj)
	Construct a UsdLodDistanceHeuristic on the prim held by `schemaObj` .

virtual USDLOD_API	~UsdLodDistanceHeuristic ()
	Destructor.

USDLOD_API UsdAttribute	GetCenterAttr () const
	The center point of this LOD Root in local coordinates.

USDLOD_API UsdAttribute	CreateCenterAttr (VtValue const &defaultValue=VtValue(), bool writeSparsely=false) const
	See GetCenterAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

USDLOD_API UsdAttribute	GetThresholdsAttr () const
	This defines the distance thresholds for LOD transitions in ascending order.

USDLOD_API UsdAttribute	CreateThresholdsAttr (VtValue const &defaultValue=VtValue(), bool writeSparsely=false) const
	See GetThresholdsAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

USDLOD_API UsdAttribute	GetBlendThresholdsAttr () const
	This defines distance thresholds for LOD transitions in ascending order.

USDLOD_API UsdAttribute	CreateBlendThresholdsAttr (VtValue const &defaultValue=VtValue(), bool writeSparsely=false) const
	See GetBlendThresholdsAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

USDLOD_API UsdRelationship	GetBoundingVolumeRel () const
	Optional relationship to a Boundable prim that defines the bounding volume for this LOD Root, the prim's extent will be used for distance calculation if it is valid (not empty).

USDLOD_API UsdRelationship	CreateBoundingVolumeRel () const
	See GetBoundingVolumeRel(), and also Create vs Get Property Methods for when to use Get vs Create.

USDLOD_API UsdLodDistanceHeuristicQuery	CreateDistanceHeuristicQuery (UsdTimeCode time=UsdTimeCode::Default()) const
	Return a UsdLodDistanceHeuristicQuery that matches the current attribute values of this UsdLodDistanceHeuristic.

USDLOD_API double	ComputeDistance (const GfVec3d &viewpoint, const GfMatrix4d &transform, UsdTimeCode time=UsdTimeCode::Default()) const
	Calculate a distance given a `viewpoint` and a `transform`.

USDLOD_API double	ComputeDistance (const GfVec3d &viewpoint, const GfMatrix4d &transform, double prevDistance, double hysteresis, UsdTimeCode time=UsdTimeCode::Default()) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. Calculate a distance given a `viewpoint` and a `transform` with hysteresis.

USDLOD_API float	ComputeLOD (double distance, UsdTimeCode time=UsdTimeCode::Default()) const
	Calculate an LOD index given a `distance`.

USDLOD_API float	ComputeLOD (const GfVec3d &viewpoint, const GfMatrix4d &transform, UsdTimeCode time=UsdTimeCode::Default()) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. Compute an LOD index given a `viewpoint` and a `transform`.

USDLOD_API float	ComputeLOD (const GfVec3d &viewpoint, const GfMatrix4d &transform, double prevDistance, double hysteresis, double *distanceOut, UsdTimeCode time=UsdTimeCode::Default()) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Public Member Functions inherited from UsdLodHeuristic
	UsdLodHeuristic (const UsdPrim &prim=UsdPrim())
	Construct a UsdLodHeuristic on UsdPrim `prim` .

	UsdLodHeuristic (const UsdSchemaBase &schemaObj)
	Construct a UsdLodHeuristic on the prim held by `schemaObj` .

virtual USDLOD_API	~UsdLodHeuristic ()
	Destructor.

USDLOD_API UsdAttribute	GetLodDomainAttr () const
	The "domain" of this heuristic.

USDLOD_API UsdAttribute	CreateLodDomainAttr (VtValue const &defaultValue=VtValue(), bool writeSparsely=false) const
	See GetLodDomainAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

Public Member Functions inherited from UsdTyped
	UsdTyped (const UsdPrim &prim=UsdPrim())
	Construct a UsdTyped on UsdPrim `prim` .

	UsdTyped (const UsdSchemaBase &schemaObj)
	Construct a UsdTyped on the prim held by `schemaObj` .

virtual USD_API	~UsdTyped ()
	Destructor.

Public Member Functions inherited from UsdSchemaBase
bool	IsConcrete () const
	Returns whether or not this class corresponds to a concrete instantiable prim type in scene description.

bool	IsTyped () const
	Returns whether or not this class inherits from UsdTyped.

bool	IsAPISchema () const
	Returns whether this is an API schema or not.

bool	IsAppliedAPISchema () const
	Returns whether this is an applied API schema or not.

bool	IsMultipleApplyAPISchema () const
	Returns whether this is an applied API schema or not.

UsdSchemaKind	GetSchemaKind () const
	Returns the kind of schema this class is.

USD_API	UsdSchemaBase (const UsdPrim &prim=UsdPrim())
	Construct and store `prim` as the held prim.

USD_API	UsdSchemaBase (const UsdSchemaBase &otherSchema)
	Construct and store for the same prim held by `otherSchema`.

virtual USD_API	~UsdSchemaBase ()
	Destructor.

UsdPrim	GetPrim () const
	Return this schema object's held prim.

SdfPath	GetPath () const
	Shorthand for GetPrim()->GetPath().

USD_API const UsdPrimDefinition *	GetSchemaClassPrimDefinition () const
	Return the prim definition associated with this schema instance if one exists, otherwise return null.

USD_API	operator bool () const
	Return true if this schema object is compatible with its held prim, false otherwise.

Static Public Member Functions
static USDLOD_API const TfTokenVector &	GetSchemaAttributeNames (bool includeInherited=true)
	Return a vector of names of all pre-declared attributes for this schema class and all its ancestor classes.

static USDLOD_API UsdLodDistanceHeuristic	Get (const UsdStagePtr &stage, const SdfPath &path)
	Return a UsdLodDistanceHeuristic holding the prim adhering to this schema at `path` on `stage`.

static USDLOD_API UsdLodDistanceHeuristic	Define (const UsdStagePtr &stage, const SdfPath &path)
	Attempt to ensure a UsdPrim adhering to this schema at `path` is defined (according to UsdPrim::IsDefined()) on this stage.

Static Public Member Functions inherited from UsdLodHeuristic
static USDLOD_API const TfTokenVector &	GetSchemaAttributeNames (bool includeInherited=true)
	Return a vector of names of all pre-declared attributes for this schema class and all its ancestor classes.

static USDLOD_API UsdLodHeuristic	Get (const UsdStagePtr &stage, const SdfPath &path)
	Return a UsdLodHeuristic holding the prim adhering to this schema at `path` on `stage`.

Static Public Member Functions inherited from UsdTyped
static USD_API const TfTokenVector &	GetSchemaAttributeNames (bool includeInherited=true)
	Return a vector of names of all pre-declared attributes for this schema class and all its ancestor classes.

static USD_API UsdTyped	Get (const UsdStagePtr &stage, const SdfPath &path)
	Return a UsdTyped holding the prim adhering to this schema at `path` on `stage`.

Static Public Member Functions inherited from UsdSchemaBase
static const TfTokenVector &	GetSchemaAttributeNames (bool includeInherited=true)

Static Public Attributes
static const UsdSchemaKind	schemaKind = UsdSchemaKind::ConcreteTyped
	Compile time constant representing what kind of schema this class is.

Static Public Attributes inherited from UsdLodHeuristic
static const UsdSchemaKind	schemaKind = UsdSchemaKind::AbstractTyped
	Compile time constant representing what kind of schema this class is.

Static Public Attributes inherited from UsdTyped
static const UsdSchemaKind	schemaKind = UsdSchemaKind::AbstractBase
	Compile time constant representing what kind of schema this class is.

Static Public Attributes inherited from UsdSchemaBase
static const UsdSchemaKind	schemaKind = UsdSchemaKind::AbstractBase
	Compile time constant representing what kind of schema this class is.

Protected Member Functions
USDLOD_API UsdSchemaKind	_GetSchemaKind () const override
	Returns the kind of schema this class belongs to.

Protected Member Functions inherited from UsdLodHeuristic
USDLOD_API UsdSchemaKind	_GetSchemaKind () const override
	Returns the kind of schema this class belongs to.

Protected Member Functions inherited from UsdTyped
USD_API UsdSchemaKind	_GetSchemaKind () const override
	Returns the kind of schema this class belongs to.

USD_API bool	_IsCompatible () const override
	Subclasses may override _IsCompatible to do specific compatibility checking with the given prim, such as type compatibility or value compatibility.

Protected Member Functions inherited from UsdSchemaBase
virtual UsdSchemaKind	_GetSchemaType () const

const TfType &	_GetType () const

USD_API UsdAttribute	_CreateAttr (TfToken const &attrName, SdfValueTypeName const &typeName, bool custom, SdfVariability variability, VtValue const &defaultValue, bool writeSparsely) const

Friends
class	UsdSchemaRegistry

Detailed Description

This LOD heuristic selects LOD children on the basis of distance from the view point to the LOD root.

The LOD child selected is determined by the comparing the computed distance with the values in thresholds and blendThresholds. Providing values in blendThresholds can allow the renderer to blend between different LOD children which can be useful to avoid flickering between two LODs. Alternatively, hysteresis can be employed to avoid changing the LOD when the distance changes by a small amount.

The center and boundingVolume properties describe geometric information for the Root prim that informs the distance calculation. If boundingVolume is authored and has a valid extent, the distance to the nearest point on the extent box is used; otherwise the distance to the center is used. Both center and boundingVolume coordinates are assumed to be in the local coordinate system of the LOD root. (Note that this heuristic prim may have a completely different coordinate system than that of the root.)

Definition at line 61 of file distanceHeuristic.h.

Constructor & Destructor Documentation

◆ UsdLodDistanceHeuristic() [1/2]

UsdLodDistanceHeuristic ( const UsdPrim & prim = UsdPrim() )

inlineexplicit

Construct a UsdLodDistanceHeuristic on UsdPrim prim .

Equivalent to UsdLodDistanceHeuristic::Get(prim.GetStage(), prim.GetPath()) for a valid prim, but will not immediately throw an error for an invalid prim

Definition at line 73 of file distanceHeuristic.h.

◆ UsdLodDistanceHeuristic() [2/2]

UsdLodDistanceHeuristic ( const UsdSchemaBase & schemaObj )

inlineexplicit

Construct a UsdLodDistanceHeuristic on the prim held by schemaObj .

Should be preferred over UsdLodDistanceHeuristic(schemaObj.GetPrim()), as it preserves SchemaBase state.

Definition at line 81 of file distanceHeuristic.h.

◆ ~UsdLodDistanceHeuristic()

virtual USDLOD_API ~UsdLodDistanceHeuristic ( )

virtual

Destructor.

Member Function Documentation

◆ _GetSchemaKind()

USDLOD_API UsdSchemaKind _GetSchemaKind ( ) const

overrideprotectedvirtual

Returns the kind of schema this class belongs to.

See also: UsdSchemaKind

Reimplemented from UsdSchemaBase.

◆ ComputeDistance() [1/2]

USDLOD_API double ComputeDistance	(	const GfVec3d &	viewpoint,
		const GfMatrix4d &	transform,
		double	prevDistance,
		double	hysteresis,
		UsdTimeCode	time = UsdTimeCode::Default() ) const

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. Calculate a distance given a viewpoint and a transform with hysteresis.

The arguments prevDistance and hysteresis should contain the most recently calculated distance and a hysteresis threshold respectively. If the actual distance is within hysteresis distance of prevDistance then prevDistance is returned. If the actual distance is outside the hysteresis window then the returned value lags behind the actual value by hysteresis. Specifically, if the actual distance is greater than prevDistance + hysteresis then the calculated distance - hysteresis is returned and if it is less than prevDistance - hysteresis then the calculated distance + hysteresis is returned. This helps prevent flickering between LOD levels when the computed size is very close to a threshold value.

See also: UsdLodDistanceHeuristicQuery::ComputeLOD

Definition at line 338 of file distanceHeuristic.h.

◆ ComputeDistance() [2/2]

USDLOD_API double ComputeDistance	(	const GfVec3d &	viewpoint,
		const GfMatrix4d &	transform,
		UsdTimeCode	time = UsdTimeCode::Default() ) const

inline

Calculate a distance given a viewpoint and a transform.

The matrix transform should convert from the root's local coordinate space to viewpoint's coordinate space. Typically, viewpoint will be specified in world coordinates and transform will convert from the root's object coordinates to world coordinates.

If transform is close to singular then any extent is ignored and the distance is calculated from viewpoint to center.

See also: UsdLodDistanceHeuristic::ComputeLOD

Definition at line 311 of file distanceHeuristic.h.

◆ ComputeLOD() [1/3]

USDLOD_API float ComputeLOD	(	const GfVec3d &	viewpoint,
		const GfMatrix4d &	transform,
		double	prevDistance,
		double	hysteresis,
		double *	distanceOut,
		UsdTimeCode	time = UsdTimeCode::Default() ) const

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Compute an LOD index given a viewpoint, a transform, a prevDistance, and a hysteresis value.

Compute the distance given the input arguments, then compute the LOD index from that distance. The computed distance is stored in the double pointed to by distanceOut.

The computed distance will be stored in distanceOut so it can be used in the next call to ComputeLOD with hysteresis.

See also: ComputeDistance for details on the hysteresis calculation.

Definition at line 416 of file distanceHeuristic.h.

◆ ComputeLOD() [2/3]

USDLOD_API float ComputeLOD	(	const GfVec3d &	viewpoint,
		const GfMatrix4d &	transform,
		UsdTimeCode	time = UsdTimeCode::Default() ) const

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. Compute an LOD index given a viewpoint and a transform.

Compute the distance given viewpoint and transform, then compute the LOD index from that distance.

Definition at line 393 of file distanceHeuristic.h.

◆ ComputeLOD() [3/3]

USDLOD_API float ComputeLOD	(	double	distance,
		UsdTimeCode	time = UsdTimeCode::Default() ) const

inline

Calculate an LOD index given a distance.

Compare the distance against the values in thresholds to determine an LOD index. If blendThresholds has values and distance is between a thresholds value and its corresponding blendThresholds value, then the returned value will be non-integral. If the renderer can blend between 2 LOD item children then it should use the returned index as follows:

float index = heuristic.ComputeLOD(distance);
if (blending_between_LOD_levels_is_active) {
    int lowIndex = int(std::floor(index));
    int highIndex = int(std::ceil(index));
    float alpha = index - lowIndex;
 
    // Display a linear interpolation using:
    //   (1-alpha) * item[lowIndex] + alpha * item[highIndex]
} else {
    int index = int(std::round(index))
 
    // Display item[index]
}

If blendThresholds is not set then only integer valued results will ever be returned.

See also: UsdLodDistanceHeuristic::ComputeDistance

Definition at line 379 of file distanceHeuristic.h.

◆ CreateBlendThresholdsAttr()

USDLOD_API UsdAttribute CreateBlendThresholdsAttr	(	VtValue const &	defaultValue = VtValue(),
		bool	writeSparsely = false ) const

See GetBlendThresholdsAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

If specified, author defaultValue as the attribute's default, sparsely (when it makes sense to do so) if writeSparsely is true - the default for writeSparsely is false.

◆ CreateBoundingVolumeRel()

USDLOD_API UsdRelationship CreateBoundingVolumeRel ( ) const

See GetBoundingVolumeRel(), and also Create vs Get Property Methods for when to use Get vs Create.

◆ CreateCenterAttr()

USDLOD_API UsdAttribute CreateCenterAttr	(	VtValue const &	defaultValue = VtValue(),
		bool	writeSparsely = false ) const

See GetCenterAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

If specified, author defaultValue as the attribute's default, sparsely (when it makes sense to do so) if writeSparsely is true - the default for writeSparsely is false.

◆ CreateDistanceHeuristicQuery()

USDLOD_API UsdLodDistanceHeuristicQuery CreateDistanceHeuristicQuery ( UsdTimeCode time = UsdTimeCode::Default() ) const

Return a UsdLodDistanceHeuristicQuery that matches the current attribute values of this UsdLodDistanceHeuristic.

The UsdLodDistanceHeuristicQuery can be used to perform LOD calculations in a renderer without referencing back to the original USD data.

◆ CreateThresholdsAttr()

USDLOD_API UsdAttribute CreateThresholdsAttr	(	VtValue const &	defaultValue = VtValue(),
		bool	writeSparsely = false ) const

See GetThresholdsAttr(), and also Create vs Get Property Methods for when to use Get vs Create.

If specified, author defaultValue as the attribute's default, sparsely (when it makes sense to do so) if writeSparsely is true - the default for writeSparsely is false.

◆ Define()

static USDLOD_API UsdLodDistanceHeuristic Define	(	const UsdStagePtr &	stage,
		const SdfPath &	path )

static

Attempt to ensure a UsdPrim adhering to this schema at path is defined (according to UsdPrim::IsDefined()) on this stage.

If a prim adhering to this schema at path is already defined on this stage, return that prim. Otherwise author an SdfPrimSpec with specifier == SdfSpecifierDef and this schema's prim type name for the prim at path at the current EditTarget. Author SdfPrimSpec s with specifier == SdfSpecifierDef and empty typeName at the current EditTarget for any nonexistent, or existing but not Defined ancestors.

The given path must be an absolute prim path that does not contain any variant selections.

If it is impossible to author any of the necessary PrimSpecs, (for example, in case path cannot map to the current UsdEditTarget's namespace) issue an error and return an invalid UsdPrim.

Note that this method may return a defined prim whose typeName does not specify this schema class, in case a stronger typeName opinion overrides the opinion at the current EditTarget.

◆ Get()

static USDLOD_API UsdLodDistanceHeuristic Get	(	const UsdStagePtr &	stage,
		const SdfPath &	path )

static

Return a UsdLodDistanceHeuristic holding the prim adhering to this schema at path on stage.

If no prim exists at path on stage, or if the prim at that path does not adhere to this schema, return an invalid schema object. This is shorthand for the following:

UsdLodDistanceHeuristic(stage->GetPrimAtPath(path));

UsdLodDistanceHeuristic::UsdLodDistanceHeuristic

UsdLodDistanceHeuristic(const UsdPrim &prim=UsdPrim())

Construct a UsdLodDistanceHeuristic on UsdPrim prim .

Definition distanceHeuristic.h:73

◆ GetBlendThresholdsAttr()

USDLOD_API UsdAttribute GetBlendThresholdsAttr ( ) const

This defines distance thresholds for LOD transitions in ascending order.

If the blend threshold values are defined, then the calculation can return a result between two levels of detail that can be used to blend or combine multiple LOD items.

For example if:

thresholds is [10.0, 50.0, 100.0]
blendThresholds is [11.0, 55.0, 110.0]

then:

Use LOD 0 when distance < 10.0
Blend LOD 0 and LOD 1 when 10.0 <= distance < 11.0
Use LOD 1 when 11.0 <= distance < 50.0
Blend LOD 1 and LOD 2 when 50 <= distance < 55.0
Use LOD 2 when 55.0 <= distance < 100.0
Blend LOD 2 and LOD 3 when 100 <= distance < 110.0
Use LOD 3 when 110.0 <= distance

The blend amount should be computed linearly between the corresponding thresholds and blendThresholds values. See thresholds for additional information. Note that blendThresholds values are clamped internally to the current and next thresholds values, ensuring that blending never occurs between more than 2 LOD children. Missing blendThresholds values result in no blending, just a discontinuous jump from one LOD child to the next.


Declaration	`uniform float[] blendThresholds = []`
C++ Type	VtArray<float>
Usd Type	SdfValueTypeNames->FloatArray
Variability	SdfVariabilityUniform

◆ GetBoundingVolumeRel()

USDLOD_API UsdRelationship GetBoundingVolumeRel ( ) const

Optional relationship to a Boundable prim that defines the bounding volume for this LOD Root, the prim's extent will be used for distance calculation if it is valid (not empty).

The distance will be calculated from the viewpoint to the nearest point on the extent box.

◆ GetCenterAttr()

USDLOD_API UsdAttribute GetCenterAttr ( ) const

The center point of this LOD Root in local coordinates.

This value is used to calculate the distance from the view point if the boundingVolume relationship does not target a Boundable prim.


Declaration	`point3f center = (0, 0, 0)`
C++ Type	GfVec3f
Usd Type	SdfValueTypeNames->Point3f

◆ GetSchemaAttributeNames()

static USDLOD_API const TfTokenVector & GetSchemaAttributeNames ( bool includeInherited = true )

static

Return a vector of names of all pre-declared attributes for this schema class and all its ancestor classes.

Does not include attributes that may be authored by custom/extended methods of the schemas involved.

◆ GetThresholdsAttr()

USDLOD_API UsdAttribute GetThresholdsAttr ( ) const

This defines the distance thresholds for LOD transitions in ascending order.

For example, [10.0, 50.0, 100.0] means:

Use LOD 0 when distance < 10.0
Use LOD 1 when 10.0 <= distance < 50.0
Use LOD 2 when 50.0 <= distance < 100.0
Use LOD 3 when 100.0 <= distance


Declaration	`uniform float[] thresholds = []`
C++ Type	VtArray<float>
Usd Type	SdfValueTypeNames->FloatArray
Variability	SdfVariabilityUniform

Friends And Related Symbol Documentation

◆ UsdSchemaRegistry

friend class UsdSchemaRegistry

friend

Definition at line 145 of file distanceHeuristic.h.

Member Data Documentation

◆ schemaKind

const UsdSchemaKind schemaKind = UsdSchemaKind::ConcreteTyped

static

Compile time constant representing what kind of schema this class is.

See also: UsdSchemaKind

Definition at line 67 of file distanceHeuristic.h.

The documentation for this class was generated from the following file:

pxr/usd/usdLod/distanceHeuristic.h

Public Member Functions

Static Public Member Functions

Static Public Attributes

Protected Member Functions

Friends

Detailed Description

Constructor & Destructor Documentation

◆ UsdLodDistanceHeuristic() [1/2]

◆ UsdLodDistanceHeuristic() [2/2]

◆ ~UsdLodDistanceHeuristic()

Member Function Documentation

◆ _GetSchemaKind()

◆ ComputeDistance() [1/2]

◆ ComputeDistance() [2/2]

◆ ComputeLOD() [1/3]

◆ ComputeLOD() [2/3]

◆ ComputeLOD() [3/3]

◆ CreateBlendThresholdsAttr()

◆ CreateBoundingVolumeRel()

◆ CreateCenterAttr()

◆ CreateDistanceHeuristicQuery()

◆ CreateThresholdsAttr()

◆ Define()

◆ Get()

◆ GetBlendThresholdsAttr()

◆ GetBoundingVolumeRel()

◆ GetCenterAttr()

◆ GetSchemaAttributeNames()

◆ GetThresholdsAttr()

Friends And Related Symbol Documentation

◆ UsdSchemaRegistry

Member Data Documentation

◆ schemaKind