This has been discussed before, but I'm not sure what you'd search for to find
it in the archives.
In the most general and conservative sense, you should set dynamic data variance
on anything you need to change.
But in reality, you only need to do this for objects that are referenced by the
draw list / render graph. Unfortunately, there is no (header file doxygen)
documentation that tells you what goes in the render graph and what doesn't. So
you can either take the conservative approach, or you can dig into the source to
determine whether you can get away with not marking something dynamic, even
though you know you're going to modify it.
For me, this boils down to a 5 second code change (to mark it dynamic) versus
possibly hours of digging into the code. So I usually take the conservative
approach.
Specifically regarding MatrixTransform, marking it as dynamic (as I did in the
Quick Start Guide) isn't necessary, as OSG's render graph is composed of copies
/ concatenations of the matrix itself, and doesn't hold references to the
MatrixTransform node per se.
Note also that data variance is used by the osgUtil::Optimizer. Other code in
OSG might also reference data variance for various purposes.
-Paul
On 2/14/2012 7:04 AM, Eric Pouliquen wrote:
Hi,
sorry to ask questions about such a classic topic but I've read lot of things
about Datavariance and would like to be sure about some points :
I've read in osg guides that the datavariance of a Drawable (and all
subclasses) and a StateSet must be set the DYNAMIC if we plan to modify its
data during object's life. This is clear.
But I also read in the QuickStart Guide in the Cow example (page 96) that the
coder set the datavariance of a MatrixTranform to DYNAMIC because he will
modify the matrix values in a callback...
So : do we need to set the datavariance to DYNAMIC for any osg Node that we
want to act on in a callback ? That point is not clear for me.
If yes, for example do we need to set a DYNAMIC datavariance for a switch node
as soon as we are going to modify its children enable states in a callback ???
Thanks a lot for your clarifications
Thank you!
Cheers,
Eric
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=45471#45471
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