Hi Richard, I'm afriad I'm not going to dive into a complex topic as I'm away on a trip, I'll try to give a quick reply to one quetion.
> So the primary question is: Why is the stategraph build from the root to > the leafs of the scenegraph and not the other way around? All OpenGL state in the OSG is inherited top down, and does so in the same way that scene graph is structured from the root at the top to the leaf at the bottom. The osgUtil::StateGraph is built as mini graph that mimics the scene graph structure and the inheritance that it implies, but contains only the elements that are visible. The state graph has to built this way to achieve the standard model of inheritance that the OSG adheres too, to do it any other way would break this inheritance convention and break most features along with it. Robert. On Wed, Apr 9, 2008 at 7:19 AM, Schmidt, Richard, SDGE1 < [EMAIL PROTECTED]> wrote: > Hi, > I got some questions about the stategraph build by osg while > culltraversal. > > So the primary question is: Why is the stategraph build from the root to > the leafs of the scenegraph and not the other way around? > > To explain it a bit, lets make an example: > > You want to display a model (a car for example), which is available as > .ive file. The model itself has a complex stateset with many > texturebinds. For each instance of the model in your scene you add a > transform node and a stateset which sets the material color. By doing so > you will loose the ability of osg to build a proper stategraph, the > stategraph becomes 'fragmented' because of setting the material color in > the parent stateset of the models graph. > > The general problem is: In the scenegraph, the parameters of the > instances are in the inner nodes (the transform nodes). In the > stategraph, the parameters of the instances are at the leaf nodes. > > Just consider another example: Lets assume you want upload > positions/rotations through uniforms to a shader. The statesets of the > uniforms have to be placed under the shader stateset to get the > stategraph sorting work properly. > > I am currently working on integrating speedtree into osg. I converted > the shaders to glsl and the parameters to uniforms. The geometry is > setup like the examples of speedtree. It's all working pretty well, but > I am stuck with the problem above. > > I'd like to organize the scenegraph as shown at the attached image > (please ignore the PositionAttitudeTransform, the position and rotations > are part of the stateset InstancesParms). > > Basics of speedtree: > *four different shaders( in the example above are just three of them) > *3 levels of statesets: > *first level: the shaders > *second level: the 'template' parameters of the model (like > texture and material properties > *third level: the instance parameters (like scale, position, > windoffset, rotation) > > Now consider adding level of detail to the graph and try to organize the > graph like osg needs it: The shaders at the root, than the 'template' > stateset and than the instances. The result is that one has to clone the > whole LOD hierarchy for each shader which is not a desired solution. > > I would prefer, if the stategraph is build from bottom up, instead of > top down. > > Greetings, > Richard > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > >
_______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
