Hi Jen, I haven't personally used the OcclusionQueryNode for work myself, perhaps Paul Martz the author of this feature might be able to chip in.
Robert. On 12 December 2012 12:39, Jen Hunter <[email protected]> wrote: > Hi Robert, > > thank you for your reply. I appreciate your help :) > > I'm sorry if I didn't express myself correctly. I also have to admit I'm > not quite the expert on computer graphics. > > Let's try to make it clearer. I want to know which of the lines on my > model are visible in a rendered image. That would be the case if a line > results in at least one drawn pixel. > > I need to have this information for an AR application which performs edge > tracking. Such approaches work with 2D-3D correspondences for each frame to > estimate the camera parameters. > The recorded webcam image of an object shows of course only the edges of > the object which are visible from the cameras point of view. To get the > correspondences I need excactly the same lines on the model (from the last > frame). > > I programmed a working OPENGL example for finding out the visible lines > using occlusion query glGetOcclusionQueryuivNV. > > At the moment I fail to understand how to make that work for OSG. I had a > look at osgocclusionquery and the used OcclusionQueryNode and understand > that it uses ARB_occlusion_query to check the pixel count. > > I tried the following but the output of the visible lines is still > incorrect: > > > Code: > > osg::Node* scene = osgDB::readNodeFile("file.dae"); > if (!scene) return 1; > > osg::Group* rootnode = new osg::Group; > rootnode->addChild(scene); > viewer.setSceneData(rootnode); > > GetLinesVisitor lineFinder; > scene->accept(lineFinder); > lines = lineFinder.getLineVector(); > > for(int i = 0; i < lines.size(); i++){ > > osg::ref_ptr<osg::OcclusionQueryNode> parent = new > osg::OcclusionQueryNode; > parent->setVisibilityThreshold( 0 ); > > osg::Geometry* linesGeom = new osg::Geometry(); > osg::Vec3Array* vertices = new osg::Vec3Array; > vertices->push_back(lines.at(i).start); > vertices->push_back(lines.at(i).end); > linesGeom->setVertexArray(vertices); > linesGeom->addPrimitiveSet(new > osg::DrawArrays(osg::PrimitiveSet::LINES,0,2)); > > osg::Geode* geode = new osg::Geode(); > geode->addDrawable(linesGeom); > parent->addChild(geode); > > > //A std::vector for all OcclusionQueryNodes. I later ask in a loop > for each element oqNodes.at(i).get()->getPassed() and count the trues > oqNodes.push_back(parent); > rootnode->addChild(parent); > } > > > > > > > So here are my questions: > > (1) How do I set up an OcclusionQueryNode for each line? > > (2) Why does the approach from my previous post not work? Is the > calculation of screen coordinates (using MVPW matrix) for a given vertex > really so imprecise that I cannot count on this being the correct > coordinates to look up in the depth buffer? > > > Cheers, > Dakota > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=51538#51538 > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >
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