In this demo, resource geometry is separated from
the 3D hierarchy so that the same resource can be used multiple
times in the 3D world. One advantage to this is animating the resource
will animate all appearances of it—the three discs
in the demo below all use the same disc resource.
Drag off objects to rotate group 3D Resource Objects -
source movie
The resources in this demo are programmed as trees,
and consist of a root node with the faces as its children. To use a resource
in the 3D world, the "resource" property of a 3Dnode is made
a reference to the root of a resource tree:
With this arrangement rendering involves traversing the
3D world tree, and when a 3Dnode uses a resource, traversing the resource
tree and rendering its nodes.
Use of Inheritance
The nodes in the two types of trees in this demo, 3D world tree and resource
trees, both need tree-related properties and methods
but also need properties and methods unique to each type of tree.
For example, nodes in the 3D world tree need a resource property
to point to a resource, while nodes in a resource tree need a list
of vectors to store geometry. Programming this using inheritance
is a good way to go.
To do that, a script called "treeNode"
is programmed as a generic tree node, with parent and
child properties and methods for managing a tree. This script serves as
the ancestor for 3Dnode and resNode, the two types of
nodes that make up the 3D world tree and resource trees, respectively.
The 3Dnode and resNode scripts contain the properties and methods unique
to their respective tree types.
Inheritance is used again for the scripts that automate
creation of different resources geometries such as cylinders, planes,
cubes, etc. These scripts inherit the resNode script and function as the
root of the resource trees. (They also inherit treeNode via resNode).
Animating the Resource
This animation uses a "spring system" which
is a bunch of objects that act on each other with spring
forces (as if they were connected by springs). The objects in this
case are the vectors that specify the outer edge of the disc resource.
These vectors are stored in the edgeVerts list of the
resDisc object.
Using forces means using the physics
model (position, velocity, acceleration):
The disc resource lies in the x-y plane
so the wave is created by animating the z coordinates
of the edge vectors.
Three spring forces act on each vector, all given by the
spring formula (restPosition - position). The first pulls
the vector back to its initial position. The second two cause the vectors
on either side to pull the vector in their direction, which creates the
wave.
The velocity is dampened so the wave eventually
dies out.
The wave is started by setting the velocity
of a vector (zVelo[i]) to a non-zero number.
•What would happen if only the first spring force
was used? What if only the last two were used?
This animation can be done in Shockwave 3D by animating
a mesh vertexList.
