RE: [Plib-devel] RE: Model Formats

[Vallevand, M. K <Mar...@UN...>]

Good.  I couldn't believe that it wouldn't work, but couldn't
see how it was done.

Regards.
Mark K Vallevand   ma...@rs...
Outside of a dog, a book is man's best friend.
 Inside of a dog, its too dark to read.  - Groucho

> 
> "Vallevand, Mark K" wrote:
> > 
> > I was looking at the SSG code for save and load.  It looks 
> like object
> > that are in the scene graph more than once are written more 
> that once.
> > So, when the load is done, one object becomes many.
> 
> I don't think so.
> 
> Check out line 309 or so of plib/src/ssg/ssgBranch.cxx,
> it uses the 'spare' field of the database node (which is
> re-used for all sorts of short-term tree-walking kinds of
> things).  As a node is written out, we set the spare field
> to a consecutively incrementing non-zero value.  When we
> try to write it out the second time, the ssgBranch code
> notices that the spare field is non-zero and instead
> writes out a special 'BACKWARDS REFERENCE' node that
> contains the 'spare' value.
> 
> When the model is reloaded, we build an ssgList of all
> the entities that are loaded - if we see a 'BACKWARDS REFERENCE'
> node - then we just link to the entry in the table pointed
> to by that 'spare' field.
> 
> This same mechanism is used to save writing out the same
> ssgState many times...and possibly other node types also.
> 
> > Is this correct, or am I dropping bits in my memory?
> 
> I *hope* you are incorrect - I went to some trouble to
> ensure that things wouldn't be written out more than once.
> 
> If this isn't working for you, please send me a concrete
> example of it failing.
> 
> -- 
> Steve Baker   HomeEmail: <sjb...@ai...>
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> 
> 
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