performBoxLayout method

@override void performBoxLayout(BoxConstraints constraints)

Perform layout with typed box constraints

Subclasses override this instead of performLayout. The default implementation sizes to the maxima, treating an unbounded axis as the corresponding lower bound.

Implementation

@override
void performBoxLayout(BoxConstraints constraints) {
  final natural = _naturalSize(_metrics);
  var desiredWidth = _width;
  var desiredHeight = _height;
  if (desiredWidth == null && desiredHeight == null) {
    desiredWidth = natural.width;
    desiredHeight = natural.height;
  } else if (desiredWidth == null) {
    desiredWidth = natural.height == 0
        ? 0
        : math.max(
            1,
            (natural.width * desiredHeight! / natural.height).round(),
          );
  } else {
    desiredHeight ??= natural.width == 0
        ? 0
        : math.max(
            1,
            (natural.height * desiredWidth / natural.width).round(),
          );
  }
  size = Size(
    constraints.constrainWidth(desiredWidth),
    constraints.constrainHeight(desiredHeight ?? natural.height),
  );
}