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}) {
  box = PdfRect.fromPoints(
    PdfPoint.zero,
    BoxConstraints(
      minWidth: double.infinity,
      minHeight: minHeight ?? 4.0,
    ).enforce(constraints).smallest,
  );
}