layout method
      
  
void
layout(
    
- Context context,
- BoxConstraints constraints, {
- bool parentUsesSize = false,
override
    First widget pass to calculate the children layout and bounding box
Implementation
@override
void layout(Context context, BoxConstraints constraints,
    {bool parentUsesSize = false}) {
  _child ??= build(context);
  if (_child != null) {
    _child!.layout(context, constraints, parentUsesSize: parentUsesSize);
    assert(_child!.box != null);
    box = _child!.box;
  } else {
    box = PdfRect.fromPoints(PdfPoint.zero, constraints.smallest);
  }
}