Engines are what make things change in an image that you have created
with Open Inventor. Animation is one obvious use of an engine, but
not the only one. Engines can be used to respond to external events,
such as mouse or keyboard activity. To realize the full power of
engines you would need to do some C++ programming, but there are some
simple animation effects that you can create in an IV file.
The basic ideas of using an engine in a .iv file are:
It has one or more input fields. You connect an input to some
other field in your scene graph. When that other field changes, the
input to the engine changes. The engine then takes some action in
response to the input change. Each input field can only be connected
to one thing.
It has one or more output fields. This is where the actions of the
engine are visible. You connect the output fields to other portions
of your scene graph, so that the current state of the scene graph will
change whenever the output of the engine changes. Each output field
can be connected to more than one thing.
It is an instance of one of Inventor's engine classes. While it is
possible to specify engines other than those that come with Inventor,
this is only useful if you are doing some C++ programming to extend
Inventor in some way. In practice there are a small number of engine
types that you will want to use for animation, and they will usually
be driven (either directly or indirectly) by the computer's own
internal clock. In other words, for animations you will often connect
an input field of an engine to some other field in your scene graph
that responds in some way to changes in time.
10.1 Types of Engines
These are just a few of the engines available in Open Inventor,
specifically listed here because they can be used effectively
without doing any C++ programming.
If you want detailed information about engines, you can browse
through chapter 13 of Inventor Mentor. It is oriented
towards C++ programming, but gives a good overview of some of the
concepts for what engines can do and how they work.
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