lerp method Null safety

Gradient? lerp(
  1. LinearShadedSteps? a,
  2. LinearShadedSteps? b,
  3. double t
)
override

Linearly interpolate between two LinearSteps.

If either LinearSteps is null, this function linearly interpolates from a LinearSteps that matches the other in begin, end, 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 Gradient? lerp(LinearShadedSteps? a, LinearShadedSteps? 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);
  // return GradientTween(begin: a, end: b).lerp(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 LinearShadedSteps(
    // shadeFactor:StepTween(begin: a.shadeFactor,end: b.shadeFactor).lerp(t),
    shadeFactor: math.max(
        0.0, ui.lerpDouble(a.shadeFactor, b.shadeFactor.toDouble(), t)!),
    distance: math.max(0.0, ui.lerpDouble(a.distance, b.distance, t)!),
    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,
    begin: AlignmentGeometry.lerp(a.begin, b.begin, t)!,
    end: AlignmentGeometry.lerp(a.end, b.end, t)!,
  );
}