# lerp method Null safety

lerp(
1. a,
2. b,
)
override

Linearly interpolate between two RadialStepss.

If either gradient is null, this function linearly interpolates from a a gradient that matches the other gradient in center, radius, stops and tileMode and with the same colors but transparent (using scale).

The t argument represents a position on the timeline, with 0.0 meaning that the interpolation has not started, returning a (or something equivalent to a); 1.0 meaning that the interpolation has finished, returning b (or something equivalent to b); and values in between 0.0 < t < 1.0 meaning that the interpolation is at the relevant point as a percentage along the timeline between a and b.

The interpolation can be extrapolated beyond 0.0 and 1.0, so negative values and values greater than 1.0 are valid (and can easily be generated by curves such as Curves.elasticInOut).

Values for t are usually obtained from an Animation<double>, such as an AnimationController.

## Implementation

static RadialSteps? lerp(RadialSteps? a, RadialSteps? b, double t) {
if (a == null && b == null) return null;
if (a == null) return b!.scale(t);
if (b == null) return a.scale(1.0 - t);
// final stretched = PrimitiveGradient.fromStretchLerp(a, b, t);
// final interpolated = PrimitiveGradient.byProgressiveMerge(
//     t < 0.5 ? PrimitiveGradient.from(a) : stretched,
//     t < 0.5 ? stretched : PrimitiveGradient.from(b),
//     // t < 0.5 ? t * 2 : (t - 0.5) * 2);
//     t);

final interpolated = PrimitiveGradient.byCombination(a, b, t);
// final interpolated = PrimitiveGradient.fromStretchLerp(a, b, t);
// final interpolated = PrimitiveGradient.byProgressiveMerge(
// PrimitiveGradient.from(a), PrimitiveGradient.from(b), t);
return RadialSteps(
softness: math.max(0.0, ui.lerpDouble(a.softness, b.softness, t)!),
colors: interpolated.colors,
stops: interpolated.stops,
// TODO: Interpolate Matrix4 / GradientTransform
transform: t > 0.5 ? a.transform : b.transform,
// TODO: interpolate tile mode
tileMode: t < 0.5 ? a.tileMode : b.tileMode,
center: AlignmentGeometry.lerp(a.center, b.center, t)!,
radius: math.max(0.0, ui.lerpDouble(a.radius, b.radius, t)!),
focal: AlignmentGeometry.lerp(a.focal, b.focal, t),
focalRadius:
math.max(0.0, ui.lerpDouble(a.focalRadius, b.focalRadius, t)!),
);
}