Attribute Queries

When we query attribute via Usd.Attribute.Get(), the value source resolution is re-evaluated on every call. This can be cached by using Usd.AttributeQuery(<prim>, <attributeName>). This small change can already bring a big performance boost, when looking up a large time sample count. In our example below, it doubled the speed.

For value clips the speed increase is not as high, as the value source can vary between clips.

The Usd.AttributeQuery object has a very similar signature to the Usd.Attribute. We can also get the time sample count, bracketing time samples and time samples within an interval. For more information, check out the official API docs.

from pxr import Sdf, Usd
stage = Usd.Stage.CreateInMemory()
prim = stage.DefinePrim(Sdf.Path("/cube"), "Cube")

size_attr = prim.GetAttribute("size")
for frame in range(10000):
    size_attr.Set(frame, frame)

attr_query = Usd.AttributeQuery(prim, "size")
print(attr_query.Get(1001)) # Returns 2.0

from pxr import Tf
# Attribute
sw = Tf.Stopwatch()
sw.Start()
for frame in range(10000):
    size_attr.Get(frame)
sw.Stop()
print(sw.milliseconds) # Returns: 14
sw.Reset()
# Attribute Query
sw = Tf.Stopwatch()
sw.Start()
for frame in range(10000):
    attr_query.Get(frame)
sw.Stop()
print(sw.milliseconds) # Returns: 7
sw.Reset()

Primvars Queries

As mentioned in our properties section, we couldn't get the native FindIncrementallyInheritablePrimvars primvars API method to work correctly. That's why we implemented it ourselves here, which should be nearly as fast, as we are not doing any calls into parent prims and tracking the inheritance ourselves.

It's also a great example of when to use .PreAndPostVisit() prim range iterators.

from pxr import Sdf, Usd, UsdGeom
stage = Usd.Stage.CreateInMemory()
bicycle_prim = stage.DefinePrim(Sdf.Path("/set/garage/bicycle"), "Cube")
car_prim = stage.DefinePrim(Sdf.Path("/set/garage/car"), "Cube")
set_prim = stage.GetPrimAtPath("/set")
garage_prim = stage.GetPrimAtPath("/set/garage")
tractor_prim = stage.DefinePrim(Sdf.Path("/set/yard/tractor"), "Cube")
"""Hierarchy
/set
/set/garage
/set/garage/bicycle
/set/garage/car
/set/yard
/set/yard/tractor
"""

# Setup hierarchy primvars
primvar_api = UsdGeom.PrimvarsAPI(set_prim)
size_primvar = primvar_api.CreatePrimvar("size", Sdf.ValueTypeNames.Float)
size_primvar.Set(10)
primvar_api = UsdGeom.PrimvarsAPI(garage_prim)
size_primvar = primvar_api.CreatePrimvar("size", Sdf.ValueTypeNames.Float)
size_primvar.Set(5)
size_primvar = primvar_api.CreatePrimvar("point_scale", Sdf.ValueTypeNames.Float)
size_primvar.Set(9000)
primvar_api = UsdGeom.PrimvarsAPI(bicycle_prim)
size_primvar = primvar_api.CreatePrimvar("size", Sdf.ValueTypeNames.Float)
size_primvar.Set(2.5)

# High performance primvar check with our own cache
primvar_stack = [{}]
iterator = iter(Usd.PrimRange.PreAndPostVisit(stage.GetPseudoRoot()))
for prim in iterator:
    primvar_api = UsdGeom.PrimvarsAPI(prim)
    if not iterator.IsPostVisit():
        before_hash = hex(id(primvar_stack[-1]))
        parent_primvars = primvar_stack[-1]
        authored_primvars = {p.GetPrimvarName(): p for p in primvar_api.GetPrimvarsWithAuthoredValues()} 
        if authored_primvars and parent_primvars:
            combined_primvars = {name: p for name, p in parent_primvars.items()}
            combined_primvars.update(authored_primvars)
            primvar_stack.append(combined_primvars)
        elif authored_primvars:
            primvar_stack.append(authored_primvars)
        else:
            primvar_stack.append(parent_primvars)
        after_hash = hex(id(primvar_stack[-1]))
        print(before_hash, after_hash, prim.GetPath(), [p.GetAttr().GetPath().pathString for p in primvar_stack[-1].values()], len(primvar_stack))
    else:
        primvar_stack.pop(-1)
# Returns:
"""
0x7fea12b349c0 0x7fea12b349c0 / [] 2
0x7fea12b349c0 0x7fea12b349c0 /HoudiniLayerInfo [] 3
0x7fea12b349c0 0x7fea12bfe980 /set ['/set.primvars:size'] 3
0x7fea12bfe980 0x7fea12a89600 /set/garage ['/set/garage.primvars:size', '/set/garage.primvars:point_scale'] 4
0x7fea12a89600 0x7fea367b87c0 /set/garage/bicycle ['/set/garage/bicycle.primvars:size', '/set/garage.primvars:point_scale'] 5
0x7fea12a89600 0x7fea12a89600 /set/garage/car ['/set/garage.primvars:size', '/set/garage.primvars:point_scale'] 5
0x7fea12bfe980 0x7fea12bfe980 /set/yard ['/set.primvars:size'] 4
0x7fea12bfe980 0x7fea12bfe980 /set/yard/tractor ['/set.primvars:size'] 5
"""