isInvisible property Null safety
Whether the node is invisible.
A node whose rect is outside of the bounds of the screen and hence not reachable for users is considered invisible if its semantic information is not merged into a (partially) visible parent as indicated by isMergedIntoParent.
An invisible node can be safely dropped from the semantic tree without loosing semantic information that is relevant for describing the content currently shown on screen.
bool get isInvisible => !isMergedIntoParent && rect.isEmpty;