Re: [Plib-devel] RE: Model Formats

[Steve B. <sjb...@ai...>]

"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.

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