Hi Robert, I am working on an HDR implementation which should work on multiple channels. The method I use requires average luminance of the scene. If I use different average luminances for different channels the colors will simply not match. E.g. in a tunnel front channel will see the tunnel exit and have a higher average luminance than the side channels which only see the dark tunnel walls.
So, I do need a way to collect current average luminances of all channels and compute a single average that can be used for all (by channel I mean separate computers that are connected to separate projectors). I know that getting data back from GPU is slow but 12ms for a 4x4 texture seems extreme. glReadPixels seems to be faster, because we are able to make full screen grabs (800x600) and still keep 60hz (even w/o pbo). Some GPGPU people suggest using glReadPixels to read directly from a FBO rather than glGetTexImage, so I was wondering if there is a way to obtain the osg::FBO pointer from the camera? cheers, tugkan > Hi Tugkan, > > On Thu, Jan 14, 2010 at 12:00 PM, Tugkan Calapoglu <[email protected]> wrote: >> unfortunately that method is easy but very slow. I think it also uses >> glGetTexImage. > > An operation like glReadPixels and glGetTexImage involves the fifo > being flushed and the data copied back into main memory. These two > things together make it slow and there isn't much you can do about it > directly. > > The best way to deal with the high cost of these operations is to > avoid them completely. Try to use algorithms that can use render to > texture using FBO's and read this textures directly in other > shaders. Never try to copy the results back to the CPU/main memory, > this does force you to do more work on the GPU and rely on more > complex shaders but in the end it means that you don't have to force a > round trip to the GPU. > > Robert. > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > -- Tugkan Calapoglu ------------------------------------- VIRES Simulationstechnologie GmbH Oberaustrasse 34 83026 Rosenheim Germany phone +49.8031.463641 fax +49.8031.463645 email [email protected] internet www.vires.com ------------------------------------- Sitz der Gesellschaft: Rosenheim Handelsregister Traunstein HRB 10410 Geschaeftsfuehrer: Marius Dupuis Wunibald Karl ------------------------------------- _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
