Re: [Plib-users] Pre/Post draw callbacks on ssgBranches.

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

Jon Anderson wrote:

> I've been working on a really simple implementation of ROAM to work with
> SSG.

Very cool!

> It's split into two parts, a terrain class, and a patch class. Each
> patch is just a subset of the terrain, to facilitate frustum culling. Each
> frame, the terrain class initializes, and then tessellates each of its
> patches.

So a 'terrain' object *contains* the 'patch' objects?

Is that why you need it to be an ssgBranch-derived class?

>  After all have been tessellated, it then renders them.  It
> tessellates them all at once so that it can match edges, and avoid cracks
> in the terrain.

I get it.

> I've implemented the terrain class as an ssgBranch class, and the patches.
> But any pre or post callbacks don't get called on branches.

That's true - because of the sorting of transparency issues we discussed
about a week ago.

However, in your case, you know that all your daughter nodes have the
same ssgState (presumably) - so they'll either all be translucent - or
none of them - so it ought to be safe to use pre-/post- callbacks.

>  It seems like they only get called on leafs.  So I have to activate the tessellating
> outside of the normal ssgCullAndDraw().

That's kindof ugly - I agree.  But if you have derived your own class, why do
you need to mess with callbacks?  You can draw the scene whenever you like.

>  This isn't so bad, except it means no culling is done prior to tessellation.

Yes - I think I understand.

Can I see the code?  It would be easier to discuss.

> Does anybody have any suggestions on  how to go about this?

I think you just need to go a little deeper into the code - you can
(in principal) do the same things that an ssgLeaf does inside an ssgBranch
or vice-versa.

>  Also, has
> anybody every tried to integrate any higherlevel organization like
> quadtrees or octrees into SSG?

Not that I know of...but those are pretty simple by comparison to your
efforts - all you need is alternative 'cull/hot/isect' member functions
derived from an ssgBranch node.

-- 
Steve Baker   HomeEmail: <sjb...@ai...>
              WorkEmail: <sj...@li...>
              HomePage : http://web2.airmail.net/sjbaker1
              Projects : http://plib.sourceforge.net
                         http://tuxaqfh.sourceforge.net
                         http://tuxkart.sourceforge.net
                         http://prettypoly.sourceforge.net