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base_interpolation.py
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base_interpolation.py
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from numbers import Number
from typing import Sequence, Tuple, TypeVar
import numpy as np
from scipy.spatial.transform import Rotation as R
_T = TypeVar("_T")
def default_interpolation(a: _T, b: _T, fraction: float) -> _T:
"""Default interpolation for the corresponding type;
linear interpolation for numeric, instantaneous transition otherwise.
Parameters
----------
a :
initial value
b :
final value
fraction : float
fraction to interpolate to between a and b.
Returns
----------
Interpolated value between a and b at fraction.
"""
if isinstance(a, bool) or isinstance(b, bool):
# checking this first because booleans are numbers
return interpolate_bool(a, b, fraction)
elif isinstance(a, Number) and isinstance(b, Number):
return interpolate_num(a, b, fraction)
elif isinstance(a, (list, tuple)) and isinstance(b, (list, tuple)):
return interpolate_sequence(a, b, fraction)
else:
# strings, etc.
return interpolate_bool(a, b, fraction)
def interpolate_sequence(
a: Sequence[_T], b: Sequence[_T], fraction: float
) -> Sequence[_T]:
"""Interpolation of list or tuple.
Parameters
----------
a : list or tuple
initial sequence
b : list or tuple
final sequence
fraction : float
fraction to interpolate to between a and b.
Returns
----------
: sequence of type a
Interpolated sequence between a and b at fraction.
"""
seq_cls = type(a)
gen = (default_interpolation(v0, v1, fraction) for v0, v1 in zip(a, b))
try:
seq = seq_cls(gen)
except TypeError:
# some interables, like NamedTuple, want the arguments separately
seq = seq_cls(*gen)
return seq
def interpolate_num(a: Number, b: Number, fraction: float) -> Number:
"""Linear interpolation for numeric types.
Parameters
----------
a : Number
initial value
b : Number
final value
fraction : float
fraction to interpolate to between a and b.
Returns
----------
: numeric type
Interpolated value between a and b at fraction.
"""
number_cls = type(a)
return number_cls(a + (b - a) * fraction)
def interpolate_bool(a: bool, b: bool, fraction: float) -> bool:
"""Instantaneous transition from a to b.
Parameters
----------
a :
initial value
b :
final value
fraction : float
fraction to interpolate to between a and b.
Returns
----------
a or b :
b if any step was taken into its direction, otherwise a.
"""
if fraction > 0.0:
return b
else:
return a
def interpolate_log(a: float, b: float, fraction: float) -> float:
"""Log interpolation, for camera zoom mostly.
Parameters
----------
a : float
initial value
b : float
final value
fraction : float
fraction to interpolate to between a and b.
Returns
----------
: float
Log interpolated value between a and b at fraction.
"""
c = interpolate_num(np.log10(a), np.log10(b), fraction)
return np.power(10, c)
def slerp(
a: Tuple[float, float, float],
b: Tuple[float, float, float],
fraction: float,
) -> Tuple[float, float, float]:
"""Compute Spherical linear interpolation from Euler angles,
compatible with the napari view.
Parameters
----------
a : tuple
initial tuple of Euler angles in degrees.
b : tuple
final tuple of Euler angles in degrees.
fraction : float
fraction to interpolate to between a and b.
Returns
----------
: tuple
Interpolated Euler angles between a and b at fraction.
"""
initial_rotation, final_rotation = R.from_euler(
"ZYX", [a, b], degrees=True
)
rotation_vector = (initial_rotation.inv() * final_rotation).as_rotvec()
rotation_vector *= fraction
c_rotation = initial_rotation * R.from_rotvec(rotation_vector)
return c_rotation.as_euler("ZYX", degrees=True)