3D Scenes - Game Coding Complete - page 526

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you ve never seen it, just imagine an entire case of alphabet soup laid out on a recur-

sive grid. It ' s gross.
The two methods, VOnRestore() and VOnUpdate(), simply traverse their children
nodes and recursively call the same methods. When you inherit from SceneNode
and create a new object, don s VOnRestore() or

VOnUpdate() if you happen to overload them. If you fail to do this, your children
nodes won

' t forget to call the base class '

t get these calls. The VOnRestore() method is meant to re-create any
programmatically created data after it has been lost. This is a similar concept to the
section on lost 2D DirectDraw surfaces.
The VOnUpdate() method is meant to handle animations or anything else that is
meant to be decoupled from the rendering traversal. That

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s why it is called with the
elapsed time, measured in milliseconds. You can use the elapsed time to make sure
animations or other movements happen at a consistent speed, regardless of computer
processing power. A faster CPU should always create a smoother animation, not nec-
essarily a faster one!
The VPreRender() method is meant to perform any task that must occur before
the render, such as setting render states. The VIsVisible() method performs a vis-
ibility test. The VRender() method does exactly what it advertises: it renders the
object. A recursive call to VRenderChildren() is made to traverse the scene
graph, performing all these actions for every node. The VPostRender() method is
meant to perform a postrendering action, such as restoring a render state to its origi-
nal value.
The VAddChild() method adds a child node. You

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ll see different implementations
of this interface class add children in different ways. No, you shouldn

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' t attach a node

to itself; you ll run out of stack space in your infinitely recursive scene graph before

you know what happened.

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SceneNodeProperties and RenderPass
When I first designed the ISceneNode class and the implementation class you ' ll see
in a few pages, SceneNode , the first attempt, loaded the class full of virtual accessor
methods: VGetThis() , VGetThat() , and VGetTheOtherDamnThing() . What I
really wanted was a structure of these properties and a single virtual accessor that
would give me read-only access to the data in that structure. The structure, Scene-
NodeProperties , is defined as follows:

typedef unsigned int ActorId;

class SceneNodeProperties