We are developing an osg-based application which requires the use of various
vehicle models, which we have modeled at several levels-of-detail.
The highest level of detail for each of these vehicle models include
articulated parts such as turrets that move in azimuth and guns that move in
elevation (e.g. tanks).
Because the osg file is somewhat substantial, we do not want to load the same
osg file for each entity in our simulation. If we had ten tanks to render,
loading and using ten duplicate osg files wouldn't be so bad, but we need to
support rendering dozens of different vehicle types with hundreds upon hundreds
of vehicles of each type.
Therefore we took the advice found in the OpenSceneGraph beginners guide (page
101 and 102) and have implemented a system whereby one detailed osg model is
made the shared child of dozens or hundreds of parents (each of which is an
osg::MatrixTransformation). During execution, we simply update the
rotation/translation or these MatrixTransformation nodes and our single model
is displayed in dozens or hundreds of unique locations and orientations.
But we also need this single model to be posed in a different way for each of
the represented players: Tank1's turret and gun are at different angles than
Tank2's turret and gun, etc.
So I have attempted to implement UpdateCallbacks in order to pose my tank model
each time it needs to be rendered for a given player.
On the matrixTransform for each entity, I call setUserData() with some
entity-specific data, then call setUpdateCallback with a callback object
descended from NodeCallback:
Code:
class articulatedIconCallback : public osg::NodeCallback
{
public:
// called every time a player's matrixTransform node is updated during update
traversal
virtual void operator()(osg::Node* n, osg::NodeVisitor* nv)
{
osg::ref_ptr<articulatedIconDataType> iconData =
dynamic_cast<articulatedIconDataType*> ( n->getUserData() );
if (iconData)
{
iconData->updateIcon();
}
traverse(n,nv);
}
};
In my implementation of updateIcon(), the code retrieves the entity-specific
data (MatrixTransformation->getUserData) in order to determine the turret and
gun angles for that unique player, then proceeds to descend into the node
hierarchy of the osg model, looking for nodes with specific names which mark
them as an articulation point. For instance, we look for a matrixTransform node
(internal to the osg model hierarchy) with the name "TURRET_AZIMUTH". If we
find it, we set the matrix accordingly. We carry on and do the same for gun
elevation and other articulated parts.
The problem is that this appears not to be working. All the player models are
positioned and oriented correctly, but each and every player which shares an
osg model shares the same turrent/gun angles, as if the last player processed
is applying his data to all the players.
In general, am I correct in expecting setUpdateCallback to behave this way? Is
there something specific I need to do to in order for this approach to work? Is
there a different, preferred approach I should be using? Any help will be
greatly appreciated!
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=51734#51734
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