[Plib-users] DAG issues

[Rahul C. <rah...@ya...>]

Steve:

Thanks for the clarification. I noticed that any node
thats derived from ssgEntity can have multiple
parents. Doesn't it mean that a scene graph
represented by SSG is not necessarily a Directed
Acyclic Graph ? What are the implications of this ?

I thought we only need geometry nodes (ssgLeafs) to
have multiple parents for instancing purpose. Please
let me know your thoughts. (any one who is interested)

--Rahul



--- Steve Baker <sjb...@ai...> wrote:
> Steve Baker wrote:
> 
> > > But think about a scenario where a Branch group
> has a
> > > leaf ssgRahulLeaf which is derived from ssgLeaf
> and
> > > has a different constrcutor which does not
> invoke
> > > recalcBSphere in it. Also imagine that the user
> of the
> > > ssg API did not call flatten on the scene graph
> before
> > > renedering it. Will the bounding spheres of the
> branch
> > > nodes be updated in this case ?
> 
> Oops - missed that comment.
> 
> If you fail to tell ssgRahulLeaf to do a
> recalcBSphere
> then the leaf node's bsphere will not have been
> computed,
> and (in theory) the first time the node is called
> upon to
> getBSphere, it *should* be computed.  That will
> typically
> happen the first time the scene graph is rendered.
> 
> I noticed though that ssgEntity (the base class for
> all
> scene graph nodes) does not dirty the sphere in its
> constructor function - so if you really did do that,
> things would be a little undefined.
> 
> I just fixed that by setting invalidBSphere TRUE in
> the ssgEntity constructor.
> 
> -- 
> Steve Baker                 
> http://web2.airmail.net/sjbaker1
> sjb...@ai... (home) 
> http://www.woodsoup.org/~sbaker
> sj...@ht...      (work)
> 
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