[osg-users] New to OSG, some questions (selection buffer, parametric curves)
Hi everyone, I am new to OSG, yet intend to use it for some projects. I've been through implementing some scene graph things before, I find OSG very interesting, I appreciate tight OpenGL integration (no cumbersome abstractions) and clean class design. So far I have a few questions regarding some aspects of OSG: - OpenGL selection buffer seems not recommended as a way of picking in OSG, explicit primitive intersections are used instead. Could someone please comment on this (why...)? - Support for parametric curves / surfaces (Bezier, NURBs and the likes). Are there any plan to support this directly (through GLU or other), or should I export those as polygonal data instead? Thank you very much, Raphael ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] New to OSG, some questions (selection buffer, parametric curves)
Hello Raphael, Welcome! Hope you enjoy your time working with OSG, and the community around it! - OpenGL selection buffer seems not recommended as a way of picking in OSG, explicit primitive intersections are used instead. Could someone please comment on this (why...)? I'll let others answer this one, I don't know myself. I have always found OpenGL selection buffers cumbersome to use, but with a good wrapper it should be possible to make something that works well and is easy to use I imagine. So I don't know why that was not done. - Support for parametric curves / surfaces (Bezier, NURBs and the likes). Are there any plan to support this directly (through GLU or other), or should I export those as polygonal data instead? I would like to eventually help in adding support for parametric curves and surfaces in OSG. I have used the GLU interface before and would have used that as the first step, followed by an implementation using Geometry Shaders, with the ability to select the implementation you want to use at runtime and a fallback mechanism. I think it would be really cool to support that. But I haven't gotten to it thus far... :-( If you want to start doing something in this direction, I will be glad to test and comment. And search the archives, there was a discussion related to this not too long ago, so there was obviously interest in this. Hope that helps, and again welcome. J-S -- __ Jean-Sebastien Guay[EMAIL PROTECTED] http://www.cm-labs.com/ http://whitestar02.webhop.org/ ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] New to OSG, some questions (selection buffer, parametric curves)
- OpenGL selection buffer seems not recommended as a way of picking in OSG, explicit primitive intersections are used instead. Could someone please comment on this (why...)? OpenGL's selection render mode is almost universally implemented via software rendering, and is therefore painfully slow for any moderate geometry load. It also tends to be O(n) -- your app just renders everything, even stuff no where near the pick point. You can sidestep these issues by reducing or simplifying the geometry being tested. Selection is the only (sort of direct) support OpenGL has for picking, so if you're using OpenGL and don't want to code a better method, then you're stuck with selection. Fortunately OSG has a superior alternative. One thing scene graphs are good at is spatial organization. As a result, pick testing in a scene graph is O(log(n)). Although it also runs in software, it performs simple ray/sphere intersection tests, which are much more efficient than software rasterization. Paul Martz Skew Matrix Software LLC http://www.skew-matrix.com http://www.skew-matrix.com/ 303 859 9466 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] New to OSG, some questions (selection buffer, parametric curves)
Hi J-S, Yes, geometry shaders would be a must for these (and also for subdivision surfaces). I'd be interested in contributing to these (time permitting, you know that...), although I first have to catch up with OSG. Thank you! Raphael On Feb 11, 2008 10:29 PM, Jean-Sébastien Guay [EMAIL PROTECTED] wrote: Hello Raphael, Welcome! Hope you enjoy your time working with OSG, and the community around it! - OpenGL selection buffer seems not recommended as a way of picking in OSG, explicit primitive intersections are used instead. Could someone please comment on this (why...)? I'll let others answer this one, I don't know myself. I have always found OpenGL selection buffers cumbersome to use, but with a good wrapper it should be possible to make something that works well and is easy to use I imagine. So I don't know why that was not done. - Support for parametric curves / surfaces (Bezier, NURBs and the likes). Are there any plan to support this directly (through GLU or other), or should I export those as polygonal data instead? I would like to eventually help in adding support for parametric curves and surfaces in OSG. I have used the GLU interface before and would have used that as the first step, followed by an implementation using Geometry Shaders, with the ability to select the implementation you want to use at runtime and a fallback mechanism. I think it would be really cool to support that. But I haven't gotten to it thus far... :-( If you want to start doing something in this direction, I will be glad to test and comment. And search the archives, there was a discussion related to this not too long ago, so there was obviously interest in this. Hope that helps, and again welcome. J-S -- __ Jean-Sebastien Guay[EMAIL PROTECTED] http://www.cm-labs.com/ http://whitestar02.webhop.org/ ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] New to OSG, some questions (selection buffer, parametric curves)
I didn't know software rasterizer was used... hmm, but thinking about it, it makes sense as retrieving info from the GPU has not always been an easy thing, yet selection buffer exists since a very long time. Anyway, as you said, higher level knowledge of the scene is definitely an advantage. I'll try to reproduce the same configuration (selecting a square of given width around the click in view space, think I saw a pyramid-like intersection primitive for doing this in OSG) as I did before with selection buffer. Thanks for that info, Raphael On Feb 12, 2008 2:52 AM, Paul Martz [EMAIL PROTECTED] wrote: - OpenGL selection buffer seems not recommended as a way of picking in OSG, explicit primitive intersections are used instead. Could someone please comment on this (why...)? OpenGL's selection render mode is almost universally implemented via software rendering, and is therefore painfully slow for any moderate geometry load. It also tends to be O(n) -- your app just renders everything, even stuff no where near the pick point. You can sidestep these issues by reducing or simplifying the geometry being tested. Selection is the only (sort of direct) support OpenGL has for picking, so if you're using OpenGL and don't want to code a better method, then you're stuck with selection. Fortunately OSG has a superior alternative. One thing scene graphs are good at is spatial organization. As a result, pick testing in a scene graph is O(log(n)). Although it also runs in software, it performs simple ray/sphere intersection tests, which are much more efficient than software rasterization. Paul Martz *Skew Matrix Software LLC* http://www.skew-matrix.com 303 859 9466 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
