Graphics Programs Reference
In-Depth Information
attributes of the sphere change in the Attribute Editor. In the Attribute Editor, enter
1.0
for the
X, Y,
and
Z
Scale values to reset the sphere back to its original size.
4. In the creation node of makeNurbsSphere1, change the radius from 1.0 to 2.0. The
sphere doubles in size because its radius is doubled. Switch back to the transform
node (nurbsSphere1), and note that the Scale X, Scale Y, and Scale Z attribute values
are unchanged. This is because you affected the size of the sphere through its Radius
attribute in the creation node at its root level, not through the Scale attributes in a
higher node. Any changes you make to the Scale attributes take effect after changes
in the lower node. This is a perfect example of how one node's output (here, the
Radius attribute) changes another node.
Parents and Children
A
parent node
is simply a node that passes its transformations down the hierarchy chain
to its children. A
child node
inherits the transforms of all the parents above it. So, by
using hierarchies for the Solar System exercise, you'll create a nested hierarchy of parents
and children to animate the orbital rotation of the nine planets and some of their moons.
By creating parent-child relationships, you can easily animate the orbit of a moon
around a planet while the planet orbits the Sun. With the proper hierarchy, the animation
of the planet orbiting the Sun automatically translates to the moon. In effect, the planet
takes the moon with it as it goes around the Sun.
Child nodes have their own transformations that can be coupled with any inherited
transforms from their parent, and these transformations affect them and any of their
children down the line.
The revolution of one of the planets around the Sun takes into account its moons,
but those moons can have their own animation to spin themselves around their plan-
ets. You're about to experience this firsthand as you continue the Solar System exercise.
The more you hear about these concepts in different contexts, the easier they will be to
master.
Figure 2.20 shows the Outliner and Hypergraph views with a simple hierarchy of
objects for your reference. The Outliner and Hypergraph show you the objects in your
scene in an outline and flowchart format, respectively. Both of these windows allow you
to access the different levels of nodes (the hierarchy) in a scene and are discussed further
in Chapter 3.
A top parent node called group1 holds its children
nurbsCone1
,
nurbsSphere3
, and
the nested group node
group2
. The node group2 is the parent node of nurbsSphere2 and
nurbsSphere1.
