1. override
bool hitTest(Size size, Point position)

Tests whether the given point, on a rectangle of a given size, would be considered to hit the decoration or not. For example, if the decoration only draws a circle, this function might return true if the point was inside the circle and false otherwise.

Source 

@override
bool hitTest(Size size, Point position) {
  assert(shape != null);
  assert((Point.origin & size).contains(position));
  switch (shape) {
    case BoxShape.rectangle:
      if (borderRadius != null) {
        RRect bounds = borderRadius.toRRect(Point.origin & size);
        return bounds.contains(position);
      }
      return true;
    case BoxShape.circle:
      // Circles are inscribed into our smallest dimension.
      Point center = size.center(Point.origin);
      double distance = (position - center).distance;
      return distance <= math.min(size.width, size.height) / 2.0;
  }
  assert(shape != null);
  return null;
}