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UsdLuxListAPI Class Reference

#include <listAPI.h>

+ Inheritance diagram for UsdLuxListAPI:

Public Types

enum  ComputeMode { ComputeModeConsultModelHierarchyCache, ComputeModeIgnoreCache }
 Runtime control over whether to consult stored lightList caches. More...

Public Member Functions

 UsdLuxListAPI (const UsdPrim &prim=UsdPrim())
 UsdLuxListAPI (const UsdSchemaBase &schemaObj)
virtual USDLUX_API ~UsdLuxListAPI ()
 Destructor. More...
USDLUX_API UsdAttribute GetLightListCacheBehaviorAttr () const
USDLUX_API UsdAttribute CreateLightListCacheBehaviorAttr (VtValue const &defaultValue=VtValue(), bool writeSparsely=false) const
USDLUX_API UsdRelationship GetLightListRel () const
USDLUX_API UsdRelationship CreateLightListRel () const
USDLUX_API SdfPathSet ComputeLightList (ComputeMode mode) const
USDLUX_API void StoreLightList (const SdfPathSet &) const
USDLUX_API void InvalidateLightList () const
- Public Member Functions inherited from UsdAPISchemaBase
 UsdAPISchemaBase (const UsdPrim &prim=UsdPrim())
 UsdAPISchemaBase (const UsdSchemaBase &schemaObj)
virtual USD_API ~UsdAPISchemaBase ()=0
 Destructor. More...
- Public Member Functions inherited from UsdSchemaBase
bool IsConcrete () const
bool IsTyped () const
bool IsAPISchema () const
 Returns whether this is an API schema or not. More...
bool IsAppliedAPISchema () const
bool IsMultipleApplyAPISchema () const
UsdSchemaType GetSchemaType () const
USD_API UsdSchemaBase (const UsdPrim &prim=UsdPrim())
 Construct and store prim as the held prim. More...
USD_API UsdSchemaBase (const UsdSchemaBase &otherSchema)
 Construct and store for the same prim held by otherSchema. More...
virtual USD_API ~UsdSchemaBase ()
 Destructor. More...
USD_API operator bool () const
UsdPrim GetPrim () const
 Return this schema object's held prim. More...
SdfPath GetPath () const
 Shorthand for GetPrim()->GetPath(). More...
USD_API const UsdPrimDefinitionGetSchemaClassPrimDefinition () const

Static Public Member Functions

static USDLUX_API const
GetSchemaAttributeNames (bool includeInherited=true)
static USDLUX_API UsdLuxListAPI Get (const UsdStagePtr &stage, const SdfPath &path)
static USDLUX_API UsdLuxListAPI Apply (const UsdPrim &prim)
- Static Public Member Functions inherited from UsdAPISchemaBase
static USD_API const
GetSchemaAttributeNames (bool includeInherited=true)
- Static Public Member Functions inherited from UsdSchemaBase
static const TfTokenVectorGetSchemaAttributeNames (bool includeInherited=true)

Static Public Attributes

static const UsdSchemaType schemaType = UsdSchemaType::SingleApplyAPI
- Static Public Attributes inherited from UsdAPISchemaBase
static const UsdSchemaType schemaType = UsdSchemaType::AbstractBase
- Static Public Attributes inherited from UsdSchemaBase
static const UsdSchemaType schemaType = UsdSchemaType::AbstractBase

Protected Member Functions

USDLUX_API UsdSchemaType _GetSchemaType () const override
- Protected Member Functions inherited from UsdAPISchemaBase
 UsdAPISchemaBase (const UsdPrim &prim, const TfToken &instanceName)
 UsdAPISchemaBase (const UsdSchemaBase &schemaObj, const TfToken &instanceName)
const TfToken_GetInstanceName () const
USD_API bool _IsCompatible () const override
- Protected Member Functions inherited from UsdSchemaBase
const TfType_GetType () const
USD_API UsdAttribute _CreateAttr (TfToken const &attrName, SdfValueTypeName const &typeName, bool custom, SdfVariability variability, VtValue const &defaultValue, bool writeSparsely) const


class UsdSchemaRegistry

Additional Inherited Members

- Static Protected Member Functions inherited from UsdAPISchemaBase
template<typename APISchemaType >
static APISchemaType _ApplyAPISchema (const UsdPrim &prim, const TfToken &apiSchemaName)
template<typename APISchemaType >
static APISchemaType _MultipleApplyAPISchema (const UsdPrim &prim, const TfToken &apiSchemaName, const TfToken &instanceName)

Detailed Description

API schema to support discovery and publishing of lights in a scene.

Discovering Lights via Traversal

To motivate this API, consider what is required to discover all lights in a scene. We must load all payloads and traverse all prims:

01 // Load everything on the stage so we can find all lights,
02 // including those inside payloads
03 stage->Load();
05 // Traverse all prims, checking if they are of type UsdLuxLight
06 // (Note: ignoring instancing and a few other things for simplicity)
07 SdfPathVector lights;
08 for (UsdPrim prim: stage->Traverse()) {
09 if (prim.IsA<UsdLuxLight>()) {
10 lights.push_back(i->GetPath());
11 }
12 }

This traversal – suitably elaborated to handle certain details – is the first and simplest thing UsdLuxListAPI provides. UsdLuxListAPI::ComputeLightList() performs this traversal and returns all lights in the scene:

01 UsdLuxListAPI listAPI(stage->GetPseudoRoot());
02 SdfPathVector lights = listAPI.ComputeLightList();

Publishing a Cached Light List

Consider a USD client that needs to quickly discover lights but wants to defer loading payloads and traversing the entire scene where possible, and is willing to do up-front computation and caching to achieve that.

UsdLuxListAPI provides a way to cache the computed light list, by publishing the list of lights onto prims in the model hierarchy. Consider a big set that contains lights:

01 def Xform "BigSetWithLights" (
02 kind = "assembly"
03 payload = @BigSetWithLights.usd@ // Heavy payload
04 ) {
05 // Pre-computed, cached list of lights inside payload
06 rel lightList = [
07 <./Lights/light_1>,
08 <./Lights/light_2>,
09 ...
10 ]
11 token lightList:cacheBehavior = "consumeAndContinue";
12 }

The lightList relationship encodes a set of lights, and the lightList:cacheBehavior property provides fine-grained control over how to use that cache. (See details below.)

The cache can be created by first invoking ComputeLightList(ComputeModeIgnoreCache) to pre-compute the list and then storing the result with UsdLuxListAPI::StoreLightList().

To enable efficient retrieval of the cache, it should be stored on a model hierarchy prim. Furthermore, note that while you can use a UsdLuxListAPI bound to the pseudo-root prim to query the lights (as in the example above) because it will perform a traversal over descendants, you cannot store the cache back to the pseduo-root prim.

To consult the cached list, we invoke ComputeLightList(ComputeModeConsultModelHierarchyCache):

01 // Find and load all lights, using lightList cache where available
02 UsdLuxListAPI list(stage->GetPseudoRoot());
03 SdfPathSet lights = list.ComputeLightList(
05 stage.LoadAndUnload(lights, SdfPathSet());

In this mode, ComputeLightList() will traverse the model hierarchy, accumulating cached light lists.

Controlling Cache Behavior

The lightList:cacheBehavior property gives additional fine-grained control over cache behavior:

  • The fallback value, "ignore", indicates that the lightList should be disregarded. This provides a way to invalidate cache entries. Note that unless "ignore" is specified, a lightList with an empty list of targets is considered a cache indicating that no lights are present.
  • The value "consumeAndContinue" indicates that the cache should be consulted to contribute lights to the scene, and that recursion should continue down the model hierarchy in case additional lights are added as descedants. This is the default value established when StoreLightList() is invoked. This behavior allows the lights within a large model, such as the BigSetWithLights example above, to be published outside the payload, while also allowing referencing and layering to add additional lights over that set.
  • The value "consumeAndHalt" provides a way to terminate recursive traversal of the scene for light discovery. The cache will be consulted but no descendant prims will be examined.


Where instances are present, UsdLuxListAPI::ComputeLightList() will return the instance-unique paths to any lights discovered within those instances. Lights within a UsdGeomPointInstancer will not be returned, however, since they cannot be referred to solely via paths.

For any described attribute Fallback Value or Allowed Values below that are text/tokens, the actual token is published and defined in UsdLuxTokens. So to set an attribute to the value "rightHanded", use UsdLuxTokens->rightHanded as the value.

Definition at line 180 of file listAPI.h.

Member Enumeration Documentation

Runtime control over whether to consult stored lightList caches.


Consult any caches found on the model hierarchy. Do not traverse beneath the model hierarchy.


Ignore any caches found, and do a full prim traversal.

Definition at line 329 of file listAPI.h.

Constructor & Destructor Documentation

UsdLuxListAPI::UsdLuxListAPI ( const UsdPrim prim = UsdPrim())

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

Definition at line 192 of file listAPI.h.

UsdLuxListAPI::UsdLuxListAPI ( const UsdSchemaBase schemaObj)

Construct a UsdLuxListAPI on the prim held by schemaObj . Should be preferred over UsdLuxListAPI(schemaObj.GetPrim()), as it preserves SchemaBase state.

Definition at line 200 of file listAPI.h.

virtual USDLUX_API UsdLuxListAPI::~UsdLuxListAPI ( )


Member Function Documentation

USDLUX_API UsdSchemaType UsdLuxListAPI::_GetSchemaType ( ) const

Returns the type of schema this class belongs to.

See Also

Reimplemented from UsdAPISchemaBase.

static USDLUX_API UsdLuxListAPI UsdLuxListAPI::Apply ( const UsdPrim prim)

Applies this single-apply API schema to the given prim. This information is stored by adding "ListAPI" to the token-valued, listOp metadata apiSchemas on the prim.

A valid UsdLuxListAPI object is returned upon success. An invalid (or empty) UsdLuxListAPI object is returned upon failure. See UsdPrim::ApplyAPI() for conditions resulting in failure.
See Also
USDLUX_API SdfPathSet UsdLuxListAPI::ComputeLightList ( ComputeMode  mode) const

Computes and returns the list of lights and light filters in the stage, optionally consulting a cached result.

In ComputeModeIgnoreCache mode, caching is ignored, and this does a prim traversal looking for prims of type UsdLuxLight or UsdLuxLightFilter.

In ComputeModeConsultModelHierarchyCache, this does a traversal only of the model hierarchy. In this traversal, any lights that live as model hierarchy prims are accumulated, as well as any paths stored in lightList caches. The lightList:cacheBehavior attribute gives further control over the cache behavior; see the class overview for details.

When instances are present, ComputeLightList(ComputeModeIgnoreCache) will return the instance-uniqiue paths to any lights discovered within those instances. Lights within a UsdGeomPointInstancer will not be returned, however, since they cannot be referred to solely via paths.

USDLUX_API UsdAttribute UsdLuxListAPI::CreateLightListCacheBehaviorAttr ( VtValue const defaultValue = VtValue(),
bool  writeSparsely = false 
) const

See GetLightListCacheBehaviorAttr(), and also Usd_Create_Or_Get_Property 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.

USDLUX_API UsdRelationship UsdLuxListAPI::CreateLightListRel ( ) const

See GetLightListRel(), and also Usd_Create_Or_Get_Property for when to use Get vs Create

static USDLUX_API UsdLuxListAPI UsdLuxListAPI::Get ( const UsdStagePtr &  stage,
const SdfPath path 

Return a UsdLuxListAPI 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:

USDLUX_API UsdAttribute UsdLuxListAPI::GetLightListCacheBehaviorAttr ( ) const

Controls how the lightList should be interpreted. Valid values are:

  • consumeAndHalt: The lightList should be consulted, and if it exists, treated as a final authoritative statement of any lights that exist at or below this prim, halting recursive discovery of lights.
  • consumeAndContinue: The lightList should be consulted, but recursive traversal over nameChildren should continue in case additional lights are added by descendants.
  • ignore: The lightList should be entirely ignored. This provides a simple way to temporarily invalidate an existing cache. This is the fallback behavior.
Declaration token lightList:cacheBehavior
C++ Type TfToken
Usd Type SdfValueTypeNames->Token
Allowed Values consumeAndHalt, consumeAndContinue, ignore
USDLUX_API UsdRelationship UsdLuxListAPI::GetLightListRel ( ) const

Relationship to lights in the scene.

static USDLUX_API const TfTokenVector& UsdLuxListAPI::GetSchemaAttributeNames ( bool  includeInherited = true)

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.

USDLUX_API void UsdLuxListAPI::InvalidateLightList ( ) const

Mark any stored lightlist as invalid, by setting the lightList:cacheBehavior attribute to ignore.

USDLUX_API void UsdLuxListAPI::StoreLightList ( const SdfPathSet ) const

Store the given paths as the lightlist for this prim. Paths that do not have this prim's path as a prefix will be silently ignored. This will set the listList:cacheBehavior to "consumeAndContinue".

Friends And Related Function Documentation

friend class UsdSchemaRegistry

Definition at line 257 of file listAPI.h.

Member Data Documentation

const UsdSchemaType UsdLuxListAPI::schemaType = UsdSchemaType::SingleApplyAPI

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

See Also

Definition at line 186 of file listAPI.h.

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