modify method

@override AttributesGroups modify(AttributesGroups groups, Map<String, ScaleConv<dynamic, num>> scales, AlgForm form, CoordConv coord, Offset origin,)

Modifies the position of mark items.

The aesthetic encodes are in the groups.

Note that the modifier should be functional, which means to return a new groups list as result, not to change the input groups.

Implementation

@override
AttributesGroups modify(
    AttributesGroups groups,
    Map<String, ScaleConv<dynamic, num>> scales,
    AlgForm form,
    CoordConv coord,
    Offset origin) {
  final normalZero = origin.dy;

  final AttributesGroups rst = groups.map((_) => <Attributes>[]).toList();
  for (var i = 0; i < groups.first.length; i++) {
    var minY = double.infinity;
    var maxY = double.negativeInfinity;
    for (var group in groups) {
      final attributes = group[i];
      for (var point in attributes.position) {
        final y = point.dy;
        if (y.isFinite) {
          minY = min(minY, y);
          maxY = max(maxY, y);
        }
      }
    }

    final symmetricBias = normalZero - (minY + maxY) / 2;
    for (var j = 0; j < groups.length; j++) {
      final attributes = groups[j][i];
      final oldPosition = attributes.position;
      rst[j].add(attributes.withPosition(oldPosition
          .map(
            (point) => Offset(point.dx, point.dy + symmetricBias),
          )
          .toList()));
    }
  }

  return rst;
}