OSG Version: 2.6.0
OS: Windows XP SP2
Compiler: MS Version 13.10.3077 ( .NET 2003 )
I am a little confused on how the precompile option works within OSG
2.6.0. From what I understand, the intended use is to have all gl
objects compiled in the background before they are merged with the scene
graph. I do not believe this is working as intended. Please correct me
if I am wrong about any of my assumptions.
By default, the code indicates that this option is on. This can be seen
in the constructor of the DatabasePager. As database requests are
processed, the requests are placed inside of the _dataToCompileList. A
few statements later, an if statement is evaluated to see if loaded
objects need to be compiled and that there are active graphics contexts.
This statement evaluates to true, but when it tries to obtain a compile
context for the graphics context, it returns NULL. Because of this, I
believe the objects to be compiled are being compiled on the same thread
that is rendering the scene.
void DatabasePager::DatabaseThread::run()
{
< ... Code Removed ... >
// move the databaseRequest from the front of the fileRequest to the end
of
// dataToCompile or dataToMerge lists.
if (loadedObjectsNeedToBeCompiled)
{
OpenThreads::ScopedLock<OpenThreads::Mutex>
lock(_pager->_dataToCompileList->_requestMutex);
databaseRequest->_requestQueue = _pager->_dataToCompileList.get();
_pager->_dataToCompileList->_requestList.push_back(databaseRequest);
}
< ... Code Removed ... >
if (loadedObjectsNeedToBeCompiled &&
!_pager->_activeGraphicsContexts.empty())
{
for(ActiveGraphicsContexts::iterator itr =
_pager->_activeGraphicsContexts.begin();
itr != _pager->_activeGraphicsContexts.end();
++itr)
{
osg::GraphicsContext* gc =
osg::GraphicsContext::getCompileContext(*itr);
if (gc)
{
< ... Code Removed ... >
}
}
< ... Code Removed ... >
}
I did some digging to see what needed to be provided to osgViewer to
create the compile context. I found that there was a command line
argument ( "--cc" ) that could be passed to indicate to the pager that a
compile context should be used. This allowed for a compile context to
be obtained, but the scene was no longer visible. Nodes were being
requested and being inserted into the data to compile list, but the
graphics thread seems not to be compiling the data because nothing
visually was showing up.
if (gc)
{
osg::GraphicsThread* gt = gc->getGraphicsThread();
if (gt)
{
gt->add(new DatabasePager::CompileOperation(_pager));
}
else
{
gc->makeCurrent();
_pager->compileAllGLObjects(*(gc->getState()));
gc->releaseContext();
}
}
To make it even more interesting, I NOPed out all of the if statement
and had it go straight to the first statement of the else clause, and
the terrain began showing up, minus the textures. I have not quite
figured that one out yet.
I do not claim to be an expert on the DatabasePager, but it looks like
there might be a few things wrong with the precompile option. I know it
is going to be defaulted to off in later versions of OSG, but I wanted
to do some testing with our terrains having this option on and off. To
me, it looked like having it on or off made no difference, and this is
why I started to investigate.
Can anyone confirm that this is the intended behavior of the precompile
option? Have I made any bad assumptions on how the system is intended
to work? Are there missing command line arguments that I have not
explored?
I am assuming that the graphics context created for the window is the
same graphics context that is used to precompile the data. What kind of
system is in place to make sure that only one thread has access to the
graphics context?
Thanks for any help. I'll report anything else I might find.
Ryan H. Kawicki
The Boeing Company
Training Systems & Services
Software Engineer
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