Creates a render object that positions its child.
Source
RenderPositionedBox({
RenderBox child,
double widthFactor,
double heightFactor,
FractionalOffset alignment: FractionalOffset.center
}) : _widthFactor = widthFactor,
_heightFactor = heightFactor,
super(child: child, alignment: alignment) {
assert(widthFactor == null || widthFactor >= 0.0);
assert(heightFactor == null || heightFactor >= 0.0);
}