Hi, Just curious about how cameras work in general. I would appreciate some clarification. I basically have four questions.
1) In the following message: http://www.mail-archive.com/[email protected]/msg14619.html it is said that a Slave camera can have its own scene graph. It is my understanding that the reason to be of Slave cameras are that they are dependent on their View's master camera, and (almost obviously) point to the same scene graph. The usages I can see for them are for: - 3D vision. The left eye is the master camera of the View, and the right eye is a slave camera. - the rear view mirror in a car. - Google StreetView-style car cameras, looking left/right/forward/backward/up and down. Again, in these situations, the slave camera obviously has the same scene graph as the master camera. So why would I want to define a custom scene graph for a slave camera, and how do I do that anyway? 2) I am not used to doing this (usually I just create a Camera and add it to a View, the Camera is never referenced anywhere else), but I understand that, as per their osg::Node object model inheritance, Cameras can be added to scene graphs, I guess to position them physically in the 3D space. When physically present in the scene graph, how are they being rendered, are they just processed as a regular osg::Group, or is there something else I am missing? 3) osg::Camera indirectly derives from osg::Group. This means I can add child nodes to a Camera. I might sound stupid here but I've never done that. Could you describe to me a usage scenario? If my camera is moving in a car, my car is most likely going to have a top-level group, and my camera will be declared as a leaf node in there... but won't have child nodes. When would a camera have child nodes? Spectacles in front of the field of view? Just want to know if I'm missing something here too. 4) Following up on question #3. I am a bit confused about the ReferenceFrame member of osg::Camera, which is a member inherited from osg::Transform. I read somewhere that it is possible to make the Slave camera independent from its master camera by setting its ReferenceFrame (inherited from osg::Transform) to ABSOLUTE_RF. Right? But in this case, regarding my question #3, if I *do* have renderable child nodes like Geodes below my slave Camera, and this slave Camera is declared somewhere in my scene graph, these child nodes will no longer be relatively positioned in the tree, since the ReferenceFrame of my camera is ABSOLUTE_RF. It seems to me that ReferenceFrame will in this situation serve a dual purpose for Camera: define the absolute/relative relationship to the master camera AND define the relationship of child nodes in the scene graph. This is a bit confusing. Since master/slave is a view-only concept, not a scene graph concept, I would have put the RELATIVE_RF/ABSOLUTE_RF master/slave somewhere else, in osg::View, per slave Camera. Thank you! Cheers, Fred ------------------ Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=32332#32332 _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
