layout method

@override PwBox layout(Context context, BoxConstraints constraints)

layout API.

Implementation

@override
PwBox layout(Context context, BoxConstraints constraints) {
  final MultiChildLayoutHost host = MultiChildLayoutHost(constraints, context, {
    for (final LayoutId child in children) child.id: child.child,
  });
  performLayout(host);
  final PwSize raw = size?.call(constraints) ?? _span(host, constraints);
  return GroupBox(constraints.constrain(raw), <(PwBox, PwOffset)>[
    for (final LayoutId child in children)
      if (host.boxes[child.id] != null)
        (
          host.boxes[child.id]!,
          host.offsets[child.id] ?? PwOffset.zero,
        ),
  ]);
}