R: [Plib-devel] SSG Tree help needed

[Paolo L. <p.l...@ci...>]

> -----Messaggio originale-----
> Da: pli...@li...=20
> [mailto:pli...@li...] Per conto di=20
> po...@cs...
> Inviato: sabato 19 novembre 2005 20.54
> A: pli...@li...
> Oggetto: [Plib-devel] SSG Tree help needed
>=20
>=20
> Hi! We are creating car simulation, and we are planning to=20
> use PLIB (SSG=20
> loader). I know the structure of SSG tree, but if I add some=20
> image (object)=20
> in the scence graph, I want to know in which classes the different=20
> attributes (like color, texture, animation) of that image=20
> goes?

As far as for 'adding an image to the scene graph' you mean a texture =
which
maps a (somehow flat) object, it is actually a texture attribute to a =
state.
A tipical node structure in SSG is:

ssgBranch (Transform, grouping, Range Selector, Switch, Texture =
transform,
etc.)
  |
  V
ssgLeaf (geometry, e.g. VtxArray)
  |
  V
ssgState (actually SimpleState, i.e. leaf attributes such as texture, =
color,
GL modes, etc.)

Thus, for answering the question, the different attributes go to the
ssgSimpleState class object, e.g.

  ssgSimpleState *s =3D new ssgSimpleState();
  s->setTexture( "imagefilename.ext", true, true );
  ssgLeaf *l;
  // create and fill geometry node l - ssgLeaf is just an abstract class
  l->setState( s );

About animation, we should agree on what kind of it - texture animation =
in
terms of texture transform can be accomplished in two ways:

1. inserting a ssgTextureTransform node before the ssgLeaf, and setting =
the
wanted texture transform on that;

2. setting up a pre-draw callback for the leaf node, which sets the GL
texture transform matrix, and a post-draw callback which resets it ti =
the
identity. The pre-draw one has to return 1 for the leaf to be drawn.

Choice 2. doesn't change your scene graph structure.

Other kind of animations could imply color attributes to be changed, yet =
you
have to manage for timing since there's no built-in mechanism for this. =
You
have timed swiches instead, which actually act by selecting one of =
children
nodes in a timed sequence. There should be other timed animation =
mechanisms
in SSG that you can search for in ssg.h, along with a mine of methods =
for
the standard classes which will be useful to you for your advanced apps.

> Because ssgVTable class contains the information like leaf geometry=20
> as arrays of=20
> vertex, normal, texture coordinate and colour data then what=20
> does the Root,=20
> branches and kids of the tree contains? Does kids only=20
> contains the objects=20
> of the scene?

Yes, leaf nodes contain scene objects, but are not the very last leaf in =
the
strict sense, being this the state node.

> What is exact difference between ssgRoot, ssgBaseTransform=20
> and ssgEntity? For the transform object does the ssgRoot is=20
> always be the=20
> parent node?

Regarding the realtion between a Transform and the Root node, yes and =
no,
since for structuring hierarchical transformation you'll probably create =
a
structure where a ssgTransform is one of the children of another
ssgTransform (the classic "robot arm" example). The Root node is still =
there
only for historical reasons, since latest Plib versions make =
ssgCullAndDraw
to start from a ssgBranch, and ssgLoad to return a ssgEntity.

> Kindly pls. find time to reply earliest possible.
> Thnaks a lot.
> - Poonam.

You're welcome, greetings -

Paolo Leoncini