[osg-users] Texture Caching Problem with 3.6.3/4

[Robert Osfield]

On Monday, 9 December 2019 19:57:27 UTC, Greg D wrote:
>
> My quick fix is to clear the cache on the first render (and call clear 
> thereafter).  OpenFlight files open and render fine now.  Is this a safe 
> fix?
>
> void ViewerBase::frame(double simulationTime)
> {
>     ....
> osgDB::Registry::instance()->clearObjectCache();  // ADDED TO CLEAR CACHE 
> AFTER RENDER SINCE IT BECOMES CORRUPTED
> }
>
>
Adding this line to ViewerBase is a point of information about the problem 
rather than a fix.  FYI, you can override Viewer::frame() by just 
subclassing Viewer there is no need to modify the OSG itself.  You can also 
call the clear after the frame() in your own frame loop.  However, all of 
these clearObjectCache() changes are hacks around a different problem.

>From your previous post that the change to OpenFlight's use of local cache 
vs ObjectCache indicates to me that the memory optimization of unrefering 
the osg::Image after the image data has been applied to the Textures 
texture object.  If an Texture is in the cache and could be reused *and* 
the texture object data is released between the first use but before that 
Texture is later reused.

The potential fixes are :

    Nt enable Texture::UnrefImageAfterApply  - this is set to true by the 
osgUtil::Optimizer's TextureVisitor.  Is you app call the Optimizer on 
loaded databases?
    Don't delete the graphics contexts, instead just close the window and 
reopen it when you need it.
    Don't enable the object cache usage.

A fix at the OSG would be for the OjbectCache to automatically detect the 
usage case where a Texture is in the case, it's been compiled and the image 
unreferred, the context deleted, then the Texture requested from the 
cache.   The place to do this would probably be 
ObjectCache::releaseGLObjects(osg::State* state).  It'd need to 
dynamic_cast<Texture> the Objects in the cache to find the textures then 
remove the Texture from the cache if it's got UnrefImageAfter enabled and 
no osg::Image still attached to it.

Robert.




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