[osg-users] Performance drop & higherRAMusageafterswitchingfromOSG 1.2 to latest SVN

[Marco Jez]

Hi Robert,

I've attached a modified cow.osg from which I've removed explicit 
DataVariance properties from state attributes. Just load the same model 
multiple times with OSG_NOTIFY_LEVEL set to INFO, and read the optimization 
report. Here are the results:

    osgviewer cow_undet.osg cow_undet.osg cow_undet.osg cow_undet.osg

[OSG 2.3]
...
Optimizer::optimize() doing SHARE_DUPLICATE_STATE
Num of StateSet=4
searching for duplicate attributes
Optimizer::optimize() doing FLATTEN_STATIC_TRANSFORMS
...
...

[OSG 1.2]
...
Optimizer::optimize() doing SHARE_DUPLICATE_STATE
Num of StateSet=4
state attribute list
    013DEE90  Material
    013E87E0  Material
    013E9898  Material
    0147F510  Material
    013E7F08  TexGen
    013E8F10  TexGen
...
...

As you can see, current osgUtil::Optimizer fails to share duplicate state 
attributes because their variance is set to UNSPECIFIED. I think the reason 
why nobody noticed this behaviour before is that all .osg and .ive models 
that were created with older versions of OSG have either DYNAMIC or STATIC 
variance, as the UNSPECIFIED flag was introduced later.

As for what piece of code should be fixed, I think it's much a design 
choice. A fundamental question is: what is the postcondition of 
Object::computeDataVariance()? I find it logical to state that after 
computeDataVariance() is called, the object's variance is either STATIC or 
DYNAMIC. If the function doesn't find any reason why the object should be 
tagged as dynamic, it should mark it as static. After all, if an object is 
dynamic because the user externally modifies it, it's user's responsibility 
to set its data variance accordingly.

Another concern is what an osgDB plugin should do when it reads from a 
format that doesn't provide information about data variance. Since the user 
receives only the root node of a scene graph that is created in an "opaque" 
way, should child nodes and attributes be marked as STATIC if not explicitly 
made dynamic by the plugin itself?

BTW, was the UNSPECIFIED flag really necessary? :-)

Cheers,
Marco
 
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