RE: [Algorithms] object oriented scene graph traversal

[Matthew M. <ma...@me...>]

Isn't that kind of heavy-weight, retraversing a separate graph for each sort
level?

What I finally settled on -- and your input was extremely instrumental in
this -- is to make render order and transformation dependency totally
separate issues.

I've got a little class called a transform composer that has a link to a
single (local) transform and another link to another transform composer (the
parent.) You attach the transform composer to an actor and query it when you
need it. It walks up the chain and accumulates the necessary transforms.
There's time-dependent caching to avoid re-multiplying matrices
unnecessarily. Per your recommendation, all the transforms are referenced
indirectly so that they may be instanced.

The actor itself is composed of a renderable object and an array of
attributes, which must be applied to the object before rendering, and any of
which can "veto" the render or select a different render object. I'm
considering renaming this a "prefix" or "prologue" object since what it
really does is enforce a particular order to a protocol invocation, and
could be used for render order in general.

I'm trying to get away from the hierarchy because all my objects will be
stored in an octree and I'll almost never render top-down, but still need an
efficient way to compose the proper transforms.

Seem sensible? I appreciate the input.

-- Matt



>-----Original Message-----
>From: gda...@li...
>[mailto:gda...@li...]On Behalf Of Doug
>Chism
>Sent: Tuesday, October 10, 2000 9:32 PM
>To: gda...@li...
>Subject: Re: [Algorithms] object oriented scene graph traversal
>
>
>
>> How do you apply rendering-order semantics? For example, if geometry A
>needs
>> to be rendered before geometry B because B is translucent, but they're
>just
>> in a list together, do you:
>> - rely on list order?
>> - sort at render time to account for translucency?
>> - something else?
>
>How about 2 scene graphs, an opaque and a transparent, or even
>multiple with
>orders that can be defined by the user? That way you dont have to
>go through
>the entire scene graph twice ( or more ) to get the alphas ( and other
>stuff ) to render in an order that you define.
>
>Doug Chism
>
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