interpolateMap<K, V> function Value interpolation

Map<K, Object?> Function(num) interpolateMap<K, V>(Map<K, V> a, Map<K, V> b)

Returns an interpolator between the two objects a and b.

Internally, an map template is created that has the same properties as b. For each property in b, if there exists a corresponding property in a, a generic interpolator is created for the two elements using interpolate. If there is no such property, the static value from b is used in the template. Then, for the given parameter t, the template's embedded interpolators are evaluated and the updated map template is then returned.

For example, if a is the map {"x": 0, "y": 1} and b is the map {x: 1, y: 10, z: 100}, the result of the interpolator for t = 0.5 is the map {x: 0.5, y: 5.5, z: 100}.

Map interpolation is particularly useful for dataspace interpolation, where data is interpolated rather than attribute values.

Note: no defensive copy of the template map is created; modifications of the returned map may adversely affect subsequent evaluation of the interpolator. No copy is made for performance reasons; interpolators are often part of the inner loop of animated transitions.

Implementation

Map<K, Object?> Function(num) interpolateMap<K, V>(Map<K, V> a, Map<K, V> b) {
  var i = <K, Object? Function(num)>{},
      c = <K, Object?>{},
      l = b is Map<K, num>
          ? interpolateNumber
          : b is Map<K, String>
              ? interpolateColorOrString
              : b is Map<K, Color>
                  ? interpolateRgb
                  : b is Map<K, DateTime>
                      ? interpolateDate
                      : b is Map<K, List>
                          ? interpolateList
                          : b is Map<K, Map>
                              ? interpolateMap
                              : interpolate;

  for (var MapEntry(:key, :value) in b.entries) {
    if (a.containsKey(key)) {
      i[key] = l(a[key]!, value);
    } else {
      c[key] = value;
    }
  }

  return (t) {
    for (var MapEntry(:key, :value) in i.entries) {
      c[key] = value(t);
    }
    return c;
  };
}