When resolving inputs of a node the visible parent node of each input
node (i.e. the first parent which is rendered to the screen) needs to be
found, and since such a node may contain several input OpNodes a map
of the visible parent to all the input OpNodes it contains is provided by
opNodes.
When resolving inputs of a node the visible parent node of each input node (i.e. the first parent which is rendered to the screen) needs to be found, and since such a node may contain several input OpNodes a map of the visible parent to all the input OpNodes it contains is provided by opNodes.