Game Development Reference
In-Depth Information
Listing 10-8. Excerpt from HierarchyTest.java; Implementing a Simple Hierarchical System
class
HierarchyScreen
extends
GLScreen {
Vertices3 cube;
Texture texture;
HierarchicalObject sun;
We only added a single new member to the class, called
sun
. It represents the root of the object
hierarchy. Since all other objects are stored as children inside this
sun
object, we don't need to
store them explicitly.
public
HierarchyScreen(Game game) {
super
(game);
cube = createCube();
texture =
new
Texture(glGame, "crate.png");
sun =
new
HierarchicalObject(cube,
false
);
sun.z = −5;
HierarchicalObject planet =
new
HierarchicalObject(cube,
true
);
planet.x = 3;
planet.scale = 0.2f;
sun.children.add(planet);
HierarchicalObject moon =
new
HierarchicalObject(cube,
true
);
moon.x = 1;
moon.scale = 0.1f;
planet.children.add(moon);
}
In the constructor, we set up the hierarchical system. First, we load the texture and create the
cube mesh to be used by all the objects. Next, we create the sun crate. It does not have a
parent, and it is located at (0,0,-5) relative to the world's origin (where the virtual camera sits).
Next, we create the planet crate orbiting the sun. It's located at (0,0,3) relative to the sun, and
it has a scale of 0.2. Since the planet crate has a side length of 1 in model space, this scaling
factor will make it render with a side length of 0.2 units. The crucial step here is that we add
the planet crate to the sun crate as a child. For the moon crate, we do something similar. It is
located at (0,0,1) relative to the planet crate, and it has a scale of 0.1 units. We also add it as
a child to the planet crate. Refer to Figure
10-15
, which uses the same unit system, to get a
picture of the setup.
@Override
public void
update(
float
deltaTime) {
sun.update(deltaTime);
}
In the
update()
method, we simply tell the sun crate to update itself. It will recursively call the
same methods of all its children, which in turn call the same methods of all their children, and so
on. This will update the rotation angles of all objects in the hierarchy.
