# lerp method

Shadow lerp (Shadow a, Shadow b, double t)

Linearly interpolate between two shadows.

If either shadow is null, this function linearly interpolates from a a shadow that matches the other shadow in color but has a zero offset and a zero blurRadius.

The `t` argument represents 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 meaning that the interpolation is at the relevant point on 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 Shadow lerp(Shadow a, Shadow b, double t) {
      assert(t != null);
      if (a == null && b == null)
        return null;
      if (a == null)
        return b.scale(t);
      if (b == null)
        return a.scale(1.0 - t);
      return Shadow(
        color: Color.lerp(a.color, b.color, t),
        offset: Offset.lerp(a.offset, b.offset, t),
        blurRadius: lerpDouble(a.blurRadius, b.blurRadius, t),
      );
    }