Attributes in USD can have values from multiple sources such as
- time-samples
- linear interpolation (a value between two time-samples)
- default values
- schema fallback values
Because time-sampled Attributes can be offset and scaled when referenced / payloaded into another Layer, it can get tough to know how a composed value was resolved.
bool is_interpolated(pxr::UsdAttribute const &attribute, double frame)
{
double lower;
double upper;
bool has_time_samples;
attribute.GetBracketingTimeSamples(frame, &lower, &upper, &has_time_samples);
// XXX : `lower != upper` means "you cannot be interpolating
// between two values if there is only one value.
//
return (has_time_samples && lower != upper && lower != frame);
}def is_interpolated(attribute, frame):
"""Check if `attribute` has a "keyframe" at `frame` or if it is interpolated.
Args:
attribute (:class:`pxr.Usd.Attribute`):
Some time-varying USD object to check.
frame (int or float):
The specific point in time to check for interpolation.
Returns:
bool:
Return False if `frame` is a "keyframe" or has no
time-varying values. Otherwise, return True.
"""
bracketing = attribute.GetBracketingTimeSamples(frame)
# Note that some attributes return an empty tuple, some None, from
# GetBracketingTimeSamples(), but all will be fed into this function.
#
return bracketing and (len(bracketing) == 2) and (bracketing[0] != frame)A reference for what each USD source enum means
Usd.ResolveInfoSourceFallback: No other value found, so using the schema fallback value (e.g. Sphere.radius fallback is 1.0) Usd.ResolveInfoSourceDefault: A user-defined default value. Usd.ResolveInfoSourceValueClips: A value that comes from a value clip Usd.ResolveInfoSourceTimeSamples: A time-varying value (does not specify interpolation or not) Usd.ResolveInfoSourceNone: The attribute's value is not defined and no schema fallback exists.
This section's trick was copied from usdview