Hi Wojtek, I'm afraid I'm too overloaded to go deep into discussion on this topic. There has been lots of discussion about it over the years so I'd recommend checking out the archives. The upshot there aren't any easy solutions to positional state.
Robert. On Thu, Mar 27, 2008 at 11:00 AM, Wojciech Lewandowski <[EMAIL PROTECTED]> wrote: > Hi Robert, > > I think I understand these nuances when it refers to TexGenNode. But what > bothers me is a question what modelview matrix is used while applying > TexGen to OpenGL when I use TexGen as an attribute ? Is this the modelview > that CullVisitor accumulated when processing the group with texgen state > attribute ? Or is it a "random" modelview which is current when render stage > aplies texgen attribute before rendering renderleafs using this stateset ? > > I wish to use TexGen as attribute because TexGenNode behaviour seems > globally superfluous. Tex coords are generated for children as well as > sibling subgraphs of TexGenNode (I am not sure what about ancestors). I > would rather want to limit tex coord generation to children subgraphs. But I > can't sort out how to modify texgen matrix to produce exactly the same > coords as TexGenNode used to... > > Few more questions: what happens if I set two or more TexGenNodes on the > same stage somewhere in the graph. Is it allowed ? What will be their scope > ? And what happens if there is TexGenNode and some other node with TexGen > attribute on the stateset ? > > We had the occasion to test this last case and observed some TexGen > coordinate bleeding. We had TexGenNode in the graph root and one node with > environment mapping texgen attribute positioned somewhere down the graph. > For simplicity lets name this node a ENV_MAP_NODE. > > I would expect that TexGenNode coords would be used for all the drawables > except those that inherit TexGen attribute from ENV_MAP_NODE. But we saw > that ENV_MAP_NODE TexGen attribute was overriding coord generation for nodes > above in graph hierarchy whenever the ENV_MAP_NODE entered the frustum. > Should this happen ? > > Wojtek > > > > ----- Original Message ----- > From: "Robert Osfield" <[EMAIL PROTECTED]> > To: "OpenSceneGraph Users" <osg-users@lists.openscenegraph.org> > Sent: Thursday, March 27, 2008 10:27 AM > Subject: Re: [osg-users] TexGenNode vs Group with TexGen attribute > > > > Hi Wojtek, > > > > You've come across the wacky world of position OpenGL state. Normal > > OpenGL state like modes and textures etc are invarient of the current > > modelview matrix, not so for positional state these use the current > > modelview matrix to position themselves so its become crucial that you > > apply a specific modelview matrix before you apply the state otherwise > > it's position will vary widely according to what modelview matrices > > just so happens to be applied. > > > > Examples of positional state are glLight, glClipPlane and glTexGen > > EYE_LINEAR. glTexGen OBJECT_LINEAR is not positional though so it > > doesn't matter when its applied - its just like ordinary OpenGL state. > > So how does the scene graph handle this positional state? We have to > > anchor in space using a special node, osg::LightSource, osg::ClipLane > > and osg::TexGenNode all exist for this purpose. > > > > Robert. > > > > On Thu, Mar 27, 2008 at 9:16 AM, Wojciech Lewandowski > > <[EMAIL PROTECTED]> wrote: > >> > >> > >> Hi, > >> > >> Whats the difference in coord generation (in practice) between TexGenNode > >> and Group with TexGen attribute. Suppose I have the same subgraph > >> attached > >> to either such TexGenNode or such Group with TexGen. In both cases > >> TexGens > >> are eye linear and use the same texture stage. > >> > >> I expected them to produce the same tex coords but results different. So > >> I > >> am bit puzzled. What did I miss ? > >> > >> Cheers, > >> Wojtek Lewandowski > >> _______________________________________________ > >> osg-users mailing list > >> osg-users@lists.openscenegraph.org > >> > >> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > >> > >> > > _______________________________________________ > > osg-users mailing list > > osg-users@lists.openscenegraph.org > > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
