#usda 1.0
(
"This file describes the USD Lux light schemata for code generation."
subLayers = [
@usdGeom/schema.usda@
]
)
over "GLOBAL" (
customData = {
string libraryName = "usdLux"
string libraryPath = "pxr/usd/usdLux"
dictionary libraryTokens = {
dictionary lightLink = {
string doc = """
This token represents the collection name to use
with UsdCollectionAPI to represent light-linking
of a UsdLuxLight prim.
"""
}
dictionary shadowLink = {
string doc = """
This token represents the collection name to use
with UsdCollectionAPI to represent shadow-linking
of a UsdLuxLight prim.
"""
}
dictionary filterLink = {
string doc = """
This token represents the collection name to use
with UsdCollectionAPI to represent filter-linking
of a UsdLuxLightFilter prim.
"""
}
dictionary orientToStageUpAxis = {
string doc = """
This token represents the suffix for a UsdGeomXformOp
used to orient a light with the stage's up axis.
"""
}
}
}
)
{
}
class "Light" (
inherits =
doc = """Base class for all lights.
Linking
Lights can be linked to geometry. Linking controls which geometry
a light illuminates, and which geometry casts shadows from the light.
Linking is specified as collections (UsdCollectionAPI) which can
be accessed via GetLightLinkCollection() and GetShadowLinkCollection().
Note that these collections have their includeRoot set to true,
so that lights will illuminate and cast shadows from all objects
by default. To illuminate only a specific set of objects, there
are two options. One option is to modify the collection paths
to explicitly exclude everything else, assuming it is known;
the other option is to set includeRoot to false and explicitly
include the desired objects. These are complementary approaches
that may each be preferable depending on the scenario and how
to best express the intent of the light setup.
"""
customData = {
string extraIncludes = """
#include "pxr/usd/usd/collectionAPI.h" """
}
prepend apiSchemas = ["CollectionAPI:lightLink", "CollectionAPI:shadowLink"]
) {
uniform bool collection:lightLink:includeRoot = 1 (
customData = {
token apiName = ""
}
)
uniform bool collection:shadowLink:includeRoot = 1 (
customData = {
token apiName = ""
}
)
float intensity = 1 (
doc = """Scales the power of the light linearly."""
)
float exposure = 0 (
doc = """Scales the power of the light exponentially as a power
of 2 (similar to an F-stop control over exposure). The result
is multiplied against the intensity."""
)
float diffuse = 1.0 (
displayName = "Diffuse Multiplier"
doc = """A multiplier for the effect of this light on the diffuse
response of materials. This is a non-physical control."""
)
float specular = 1.0 (
displayName = "Specular Multiplier"
doc = """A multiplier for the effect of this light on the specular
response of materials. This is a non-physical control."""
)
bool normalize = false (
displayName = "Normalize Power"
doc = """Normalizes power by the surface area of the light.
This makes it easier to independently adjust the power and shape
of the light, by causing the power to not vary with the area or
angular size of the light."""
)
color3f color = (1, 1, 1) (
doc = """The color of emitted light, in energy-linear terms."""
)
bool enableColorTemperature = false (
displayName = "Enable Color Temperature"
doc = """Enables using colorTemperature."""
)
float colorTemperature = 6500 (
displayName = "Color Temperature"
doc = """Color temperature, in degrees Kelvin, representing the
white point. The default is a common white point, D65. Lower
values are warmer and higher values are cooler. The valid range
is from 1000 to 10000. Only takes effect when
enableColorTemperature is set to true. When active, the
computed result multiplies against the color attribute.
See UsdLuxBlackbodyTemperatureAsRgb()."""
)
rel filters (
doc = """Relationship to the light filters that apply to this light."""
)
}
class "ListAPI" (
inherits =
doc = """API schema to support discovery and publishing of lights in a scene.
\\section UsdLuxListAPI_Discovery 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:
\\code
01 // Load everything on the stage so we can find all lights,
02 // including those inside payloads
03 stage->Load();
04
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()) {
10 lights.push_back(i->GetPath());
11 }
12 }
\\endcode
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:
\\code
01 UsdLuxListAPI listAPI(stage->GetPseudoRoot());
02 SdfPathVector lights = listAPI.ComputeLightList();
\\endcode
\\section UsdLuxListAPI_LightList 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:
\\code
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 }
\\endcode
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):
\\code
01 // Find and load all lights, using lightList cache where available
02 UsdLuxListAPI list(stage->GetPseudoRoot());
03 SdfPathSet lights = list.ComputeLightList(
04 UsdLuxListAPI::ComputeModeConsultModelHierarchyCache);
05 stage.LoadAndUnload(lights, SdfPathSet());
\\endcode
In this mode, ComputeLightList() will traverse the model
hierarchy, accumulating cached light lists.
\\section UsdLuxListAPI_CacheBehavior Controlling Cache Behavior
The lightList:cacheBehavior property gives additional fine-grained
control over cache behavior:
\\li 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.
\\li 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.
\\li 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.
\\section UsdLuxListAPI_Instancing Instancing
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.
"""
) {
rel lightList (
doc = """Relationship to lights in the scene."""
)
token lightList:cacheBehavior (
doc = """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.
"""
allowedTokens = ["consumeAndHalt", "consumeAndContinue", "ignore"]
)
}
class "ShapingAPI" (
inherits =
doc = """Controls for shaping a light's emission."""
) {
float shaping:focus = 0 (
displayGroup = "Shaping"
doc = """A control to shape the spread of light. Higher focus
values pull light towards the center and narrow the spread.
Implemented as an off-axis cosine power exponent.
TODO: clarify semantics"""
)
color3f shaping:focusTint = (0, 0, 0) (
displayGroup = "Shaping"
doc = """Off-axis color tint. This tints the emission in the
falloff region. The default tint is black.
TODO: clarify semantics"""
)
float shaping:cone:angle = 90 (
displayGroup = "Shaping"
doc = """Angular limit off the primary axis to restrict the
light spread."""
)
float shaping:cone:softness = 0 (
displayGroup = "Shaping"
doc = """Controls the cutoff softness for cone angle.
TODO: clarify semantics"""
)
asset shaping:ies:file (
displayGroup = "Shaping"
doc = """An IES (Illumination Engineering Society) light
profile describing the angular distribution of light."""
)
float shaping:ies:angleScale = 0 (
displayGroup = "Shaping"
doc = """Rescales the angular distribution of the IES profile.
TODO: clarify semantics"""
)
bool shaping:ies:normalize = false (
displayGroup = "Shaping"
doc = """Normalizes the IES profile so that it affects the shaping
of the light while preserving the overall energy output."""
)
}
class "ShadowAPI" (
inherits =
doc = """Controls to refine a light's shadow behavior. These are
non-physical controls that are valuable for visual lighting work."""
) {
bool shadow:enable = true (
displayGroup = "Shadows"
doc = """Enables shadows to be cast by this light."""
)
color3f shadow:color = (0, 0, 0) (
displayGroup = "Shadows"
doc = """The color of shadows cast by the light. This is a
non-physical control. The default is to cast black shadows."""
)
float shadow:distance = -1.0 (
displayGroup = "Shadows"
doc = """The maximum distance shadows are cast.
The default value (-1) indicates no limit.
"""
)
float shadow:falloff = -1.0 (
displayGroup = "Shadows"
doc = """The near distance at which shadow falloff begins.
The default value (-1) indicates no falloff.
"""
)
float shadow:falloffGamma = 1.0 (
displayGroup = "Shadows"
doc = """A gamma (i.e., exponential) control over shadow strength
with linear distance within the falloff zone.
This requires the use of shadowDistance and shadowFalloff."""
)
}
class LightFilter "LightFilter" (
inherits =
doc = """A light filter modifies the effect of a light.
Lights refer to filters via relationships so that filters may be
shared.
Linking
Filters can be linked to geometry. Linking controls which geometry
a light-filter affects, when considering the light filters attached
to a light illuminating the geometry.
Linking is specified as a collection (UsdCollectionAPI) which can
be accessed via GetFilterLinkCollection().
Note however that there are extra semantics in how UsdLuxLightFilter
uses its collection: if a collection is empty, the filter is treated
as linked to all geometry for the respective purpose.
UsdCollectionAPI and UsdCollectionAPI::MembershipQuery are unaware
of this filter-specific interpretation.
"""
customData = {
string extraIncludes = """
#include "pxr/usd/usd/collectionAPI.h" """
}
prepend apiSchemas = ["CollectionAPI:filterLink"]
) {
uniform bool collection:filterLink:includeRoot = 1 (
customData = {
token apiName = ""
}
)
}
class DistantLight "DistantLight" (
inherits =
doc = """Light emitted from a distant source along the -Z axis.
Also known as a directional light."""
) {
float angle = 0.53 (
doc = """Angular size of the light in degrees.
As an example, the Sun is approximately 0.53 degrees as seen from Earth.
Higher values broaden the light and therefore soften shadow edges.
"""
)
float intensity = 50000 (
doc = """Scales the emission of the light linearly.
The DistantLight has a high default intensity to approximate the Sun."""
)
}
class DiskLight "DiskLight" (
inherits =
doc = """Light emitted from one side of a circular disk.
The disk is centered in the XY plane and emits light along the -Z axis."""
) {
float radius = 0.5 (
doc = "Radius of the disk."
)
}
class RectLight "RectLight" (
inherits =
doc = """Light emitted from one side of a rectangle.
The rectangle is centered in the XY plane and emits light along the -Z axis.
The rectangle is 1 unit in length in the X and Y axis. In the default
position, a texture file's min coordinates should be at (+X, +Y) and
max coordinates at (-X, -Y)."""
) {
float width = 1 (
doc = "Width of the rectangle, in the local X axis."
)
float height = 1 (
doc = "Height of the rectangle, in the local Y axis."
)
asset texture:file (
doc = """A color texture to use on the rectangle."""
)
}
class SphereLight "SphereLight" (
inherits =
doc = """Light emitted outward from a sphere."""
) {
float radius = 0.5 (
doc = "Radius of the sphere."
)
bool treatAsPoint = false (
doc = """A hint that this light can be treated as a 'point'
light (effectively, a zero-radius sphere) by renderers that
benefit from non-area lighting. Renderers that only support
area lights can disregard this."""
)
}
class CylinderLight "CylinderLight" (
inherits =
doc = """Light emitted outward from a cylinder.
The cylinder is centered at the origin and has its major axis on the X axis.
The cylinder does not emit light from the flat end-caps.
"""
) {
float length = 1 (
doc = "Width of the rectangle, in the local X axis."
)
float radius = 0.5 (
doc = "Radius of the cylinder."
)
bool treatAsLine = false (
doc = """A hint that this light can be treated as a 'line'
light (effectively, a zero-radius cylinder) by renderers that
benefit from non-area lighting. Renderers that only support
area lights can disregard this."""
)
}
class GeometryLight "GeometryLight" (
inherits =
doc = """Light emitted outward from a geometric prim (UsdGeomGprim),
which is typically a mesh."""
) {
rel geometry (
doc = """Relationship to the geometry to use as the light source."""
)
}
class DomeLight "DomeLight" (
inherits =
doc = """Light emitted inward from a distant external environment,
such as a sky or IBL light probe. The orientation of a dome light with a
latlong texture is expected to match the OpenEXR specification for latlong
environment maps. From the OpenEXR documentation:
-------------------------------------------------------------------------
Latitude-Longitude Map:
The environment is projected onto the image using polar coordinates
(latitude and longitude). A pixel's x coordinate corresponds to
its longitude, and the y coordinate corresponds to its latitude.
Pixel (dataWindow.min.x, dataWindow.min.y) has latitude +pi/2 and
longitude +pi; pixel (dataWindow.max.x, dataWindow.max.y) has
latitude -pi/2 and longitude -pi.
In 3D space, latitudes -pi/2 and +pi/2 correspond to the negative and
positive y direction. Latitude 0, longitude 0 points into positive
z direction; and latitude 0, longitude pi/2 points into positive x
direction.
The size of the data window should be 2*N by N pixels (width by height),
where N can be any integer greater than 0.
-------------------------------------------------------------------------
"""
) {
asset texture:file (
doc = """A color texture to use on the dome, such as an HDR (high
dynamic range) texture intended for IBL (image based lighting)."""
)
token texture:format = "automatic" (
allowedTokens = ["automatic", "latlong", "mirroredBall", "angular", "cubeMapVerticalCross"]
doc = """Specifies the parameterization of the color map file.
Valid values are:
- automatic: Tries to determine the layout from the file itself.
For example, Renderman texture files embed an explicit
parameterization.
- latlong: Latitude as X, longitude as Y.
- mirroredBall: An image of the environment reflected in a
sphere, using an implicitly orthogonal projection.
- angular: Similar to mirroredBall but the radial dimension
is mapped linearly to the angle, providing better sampling
at the edges.
- cubeMapVerticalCross: A cube map with faces laid out as a
vertical cross.
"""
)
rel portals (
doc = """Optional portals to guide light sampling."""
)
}
class LightPortal "LightPortal" (
inherits =
doc = """A rectangular portal in the local XY plane that guides sampling
of a dome light. Transmits light in the -Z direction.
The rectangle is 1 unit in length."""
) {
}