If you intend to save the results of your rendering to an osg::Image, then FBOs probably won't give you any performance benefit over rendering to the back buffer. In fact the additional cost of multiple BindBuffer calls per frame might cause a performance hit with FBOs (as opposed to rendering to the back buffer multiple times with the same rendering context, which would be faster). The cost of copying back to the host osg::Image is the same in either case.
FBOs are excellent for rendering into, then using that rendering as a texture, with no intervening copy. RTT with a frame buffer requires an intervening copy, so would be slower for that purpose. Paul Martz Skew Matrix Software LLC http://www.skew-matrix.com 303 859 9466 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf > Of nicolas martin > Sent: Thursday, February 07, 2008 8:38 AM > To: [email protected] > Subject: Re: [osg-users] performance fbo > > Well, if I understand the way it is working, the fbo saves > you the time to copy from the framebuffer to a texture, but > you still have to transfer from the texture to main memory. > But if is right, then rendering to an image should be faster > using an fbo, even when there is only one fbo (and no > overhead related to binding...), but it seems the > performances are the same whatever the method in osgprerender. > Anyway, when using a lot of rtts, I found that using fb is > really faster than using fbos, is it a problem of osg ? or > just normal due to the way fbos works ? > > So If i plan on doing a lot of rtts, saving each render to an > image (in main memory), should I stick with adding a lot of > cameras each rendering to an osg::Image with framebuffer > implementation ?? or has anybody else ever tried something else ? > > thanks > > On 6 fév, 17:21, nicolas martin <[EMAIL PROTECTED]> wrote: > > Well, let's say that i'm adding like 50 cameras so > basically 50 fbos > > ... > > But as I currently don't really understand what is the need > for fbo, > > if you're about to copy the texture to an image anyway, can anyone > > explain it to me ??? > > I'm also really interested in understanding what is exactly > osg doing > > when it is rendering to an image ... Creating an fbo (with > what format > > for the texture ??), rendering to it, and then copying it > to my image > > ?? > > > > thanks > > > > On Feb 6, 2:59 pm, "Paul Martz" <[EMAIL PROTECTED]> wrote: > > > > > How many fbos is "a lot"? Hundreds of BindBuffer calls > per frame can > > > not be a good thing, perhaps that explains the performance hit. > > > -Paul > > > > > > -----Original Message----- > > > > From: [EMAIL PROTECTED] > > > > [mailto:[EMAIL PROTECTED] On > Behalf Of > > > > [EMAIL PROTECTED] > > > > Sent: Wednesday, February 06, 2008 10:42 AM > > > > To: [EMAIL PROTECTED] > > > > Subject: [osg-users] performance fbo > > > > > > Hi all, > > > > > > I modified the osgprerender example to add a certain number of > > > > cameras, doing exactly the same thing as the one that<s > rendering > > > > to a texture, but made them render to a texture that is > not used. > > > > So in the scene, there is the main viewer, the camera > that's doing > > > > rtt, and a lot of other cameras doing rtt for nothing. > > > > What I've experienced is that by using the fbo > implementation, the > > > > fps is really lower than the one I get by using any of > the other > > > > implementation ... > > > > You may ask why I'm doing this, but I want to do a lot of rtt > > > > saving each render to an image, so I thought that just by > > > > modifying the osgprerender example, it would do the trick ... > > > > but :( Is there some kind of overhead related to using a lot of > > > > fbos compared to another method ?? > > > > > > Thanks all > > > > _______________________________________________ > > > > osg-users mailing list > > > > [EMAIL PROTECTED] > > > >http://lists.openscenegraph.org/listinfo.cgi/osg-users-opensce > > > > > negraph.org > > > > > _______________________________________________ > > > osg-users mailing list > > > > [EMAIL PROTECTED]://lists.openscenegraph. org/listinfo.cgi/osg-users-openscenegraph... > > > > _______________________________________________ > > osg-users mailing list > > > [EMAIL PROTECTED]://lists.openscenegraph. org/listinfo.cgi/osg-users-openscenegraph... > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-opensce negraph.org _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
