Hi everyone,
I've seen a lot of threads on performance issues in the mailing list but none
of them seemed to address my particular problem precisely, either because the
problem description was vague or the replies were covering a matter far too
vast to include everything in a single message. So I've decided to expose my
problem and share my observations and potential solution. My goal here is to
understand why it does what it does and maybe help some other users with
similar problems.
Here's my system configuration: Dell XPS, Intel Core2 Quad Q9300 @ 2.5 Ghz, 4
GB RAM, NVidia GeForce GTX 280. The application uses MFC classes (extended from
the OSGViewerMFC exemple) and is run under Windows Vista 32-bit.
So, I have this multi-view application with textured terrains generated from
osgGIS. I eliminated all LODs to eliminate this factor in my performance
comparison. On those terrains, we add road segments with a stateset:
mGeometrie = new osg::Geometry;
mGeometrie->setVertexArray(lListe);
mGeometrie->addPrimitiveSet(new
osg::DrawArrays(osg::PrimitiveSet::LINE_LOOP,0,1));
mGeometrie->addPrimitiveSet(new
osg::DrawArrays(osg::PrimitiveSet::POLYGON,0,1));
((osg::DrawArrays*)mGeometrie->getPrimitiveSet(0))->setCount(lListe->size());
((osg::DrawArrays*)mGeometrie->getPrimitiveSet(1))->setCount(lListe->size());
osg::ref_ptr<osg::StateSet> lStateSet = mGeometrie->getOrCreateStateSet();
lStateSet->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
osg::ref_ptr<osg::Vec4Array> lCouleur = new osg::Vec4Array;
lCouleur->push_back(osg::Vec4(1.0f, 1.0f, 0.0f, 1.0f));
mGeometrie->setColorArray(lCouleur);
mGeometrie->setColorBinding(osg::Geometry::BIND_OVERALL);
We also add a larger invisible road segment above to make things easier for the
user to select a segment (the collision is detected in a visitor):
osg::ref_ptr<osg::Geometry> lGeometrieSelection = new osg::Geometry;
lGeometrieSelection->setVertexArray(lListeSelection);
lGeometrieSelection->addPrimitiveSet(new
osg::DrawArrays(osg::PrimitiveSet::LINE_LOOP,0,1));
lGeometrieSelection->addPrimitiveSet(new
osg::DrawArrays(osg::PrimitiveSet::POLYGON,0,1));
((osg::DrawArrays*)lGeometrieSelection->getPrimitiveSet(0))->setCount(lListeSelection->size());
((osg::DrawArrays*)lGeometrieSelection->getPrimitiveSet(1))->setCount(lListeSelection->size());
osg::ref_ptr<osg::StateSet> lStateset =
lGeometrieSelection->getOrCreateStateSet();
osg::ref_ptr<osg::Material> lMateriel =
dynamic_cast<osg::Material*>(lStateset->getAttribute(osg::StateAttribute::MATERIAL));
if (!lMateriel) lMateriel = new osg::Material;
lMateriel->setTransparency(osg::Material::FRONT_AND_BACK, 1.0f);
lStateset->setAttributeAndModes( lMateriel,
osg::StateAttribute::PROTECTED | osg::StateAttribute::ON);
lStateset->setRenderingHint(osg::StateSet::TRANSPARENT_BIN);
osg::ref_ptr<osg::Vec4Array> lCouleurSelection = new osg::Vec4Array;
lCouleurSelection->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 0.0f));
lGeometrieSelection->setColorArray(lCouleurSelection);
lGeometrieSelection->setColorBinding(osg::Geometry::BIND_OVERALL);
Now, I noticed a lot of things while doing my performance experiments:
- First of all: Statesets seem to affect performance drastically and
the code above generates a lot of them. I have 4 views sharing a scene
containing 4 terrain with 15 segments each. Without the road segments, I reach
56 FPS with 237 statesets, 512K vertices and 970K primitives. When I add the
road segments, I drop to 24 FPS with 781 statesets, 544K vertices and +1M
primitives.
- Primitives and vertices count also affect performance but the effect
is less significant. Indeed, I can put 5 terrains without the road segments and
I'm still at 55 FPS with only 257 statesets, 625K vertices and +1.2M
primitives. I drop to 30 FPS with 514 statesets, 1.2M vertices and 2.4M
primitives (10 terrains with no road segments).
- With a single view, the stateset effect is far less significant.
Maybe my multi-view is not set properly?
- The FOV (set in the camera's projection matrix) also seem to affect
performance negatively and worsen the stateset effect. For now, I set it to 170
degrees (to be able to cull everything for CAVE rendering) but I think I will
need to optimize this value with tracker coordinates.
I remember Robert saying that we should avoid independent statesets. This
raises a lot of questions since I don't fully understand this functionality
yet... For instance, what is the typical amount of statesets in a commercial
application? How can we combine statesets for multiple objects potentially in
different states from each others?
Finally, do you have any idea how I could solve my particular selection problem
without having to add more statesets for the invisible but larger road
segments? Note that adding the visible segments also add a lot of statesets...
Any idea how to diminish this even more?
Thank you very much for your time (especially if you reached this line!)
Cheers,
Frederic Drolet, M. Sc.
Computing Solutions and Experimentations | Solutions informatiques et
expérimentations
Systems of Systems | Systèmes de systèmes
DRDC Valcartier | RDDC Valcartier
2459, boul. Pie-XI North
Quebec, Quebec
G3J 1X5 CANADA
Phone | Téléphone: (418) 844-4000 ext : 4820
Fax | Télécopieur: (418) 844-4538
E-mail | Courriel: frederic.dro...@drdc-rddc.gc.ca
<mailto:frederic.dro...@drdc-rddc.gc.ca>
Web : www.valcartier.drdc-rddc.gc.ca <http://www.valcartier.drdc-rddc.gc.ca>
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