232 Chapter 4 Scene Graphs
set of local transformations. The Room Contents always have the identity transfor-
mation, never to be changed. This decision has the consequence that if you only have
a single instance (most likely the common case in a scene), a parent node should be
used to indirectly access that instance. If you are not consistent in the manner of ac-
cessing the object, your engine logic must distinguish between a single instance of
an object and multiple instances of an object, then handle the situations differently.
Thus, every geometric object must be manipulated as a node-geometry pair. Worse is
that if you plan on instancing a subgraph of nodes, that subgraph must have parent
nodes through which you access the instances. Clearly ...