So with the 3.0 api change we propose the following change:
- put OSG_EXPORT on the QueryGeometry class so that we get access to the getNumPixels method.
- Create a function called getQueryGeometry that returns a casted _queryGeode->getDrawable(). Or a function called getQueryGeode that returns _queryGeode."
I move declaration of classes TestResult, QueryGeometry from cpp to header file and made a void createSupportNodes() a virtual method.
Now is possible to inherit from class OcclusionQueryNode."
* Change OcclusionQueryNode::getPassed to take a NodeVisitor rather than the distance from BS center to the eye point. Change where CullVisitor calls this method to use the new parameters.
* getPassed now exits early and returns true to avoid blinking / blink-in of geometry for the first frame or for out-of-range LOD children coming back into view.
* getPassed now considers the distance from the near plane to the bounding sphere (rather than eye point to bounding sphere) when determining if the viewer is "inside" the bounding sphere or not."
occlusion query result is not ready for retrieval when the app tries to
retrieve it. This fix adds an application-level wait loop to ensure the
result is ready for retrieval. This code is not compiled by default; add "-D
FORCE_QUERY_RESULT_AVAILABLE_BEFORE_RETRIEVAL" to get this code.
Full, gory details, to the best of my recollection:
The conditions under which we encountered this issue are as follows: 64-bit
processor, Mac/Linux OS, multiple NVIDIA GPUs, multiple concurrent draw
threads, VRJuggler/SceneView-based viewer, and a scene graph containing
OcclusionQueryNodes. Todd wrote a small test program that produces an almost
instant crash in this environment. We verified the crash does not occur in a
similar environment with a 32-bit processor, but we have not yet tested on
Windows and have not yet tested with osgViewer.
The OpenGL spec states clearly that, if an occlusion query result is not yet
ready, an app can go ahead and attempt to retrieve it, and OpenGL will
simply block until the result is ready. Indeed, this is how
OcclusionQueryNode is written, and this has worked fine on several platforms
and configurations until Todd's test program.
By trial and error and dumb luck, we were able to workaround the crash by
inserting a wait loop that forces the app to only retrieve the query after
OpenGL says it is available. As this should not be required (OpenGL should
do this implicitly, and more efficiently), the wait loop code is not
compiled by default. Developers requiring this work around must explicitly
add "-D FORCE_QUERY_RESULT_AVAILABLE_BEFORE_RETRIEVAL" to the compile
options to include the wait loop."
