[osg-users] osgscreencapture transfer speeds (PBOs slower)

2009-12-07 Thread J.P. Delport
Hi all, running with latest svn OSG, the osgscreencapture example produces the best speed for me (tested on a few machines) when run with the --no-pbo command line parameter. All the pbo options (--single-pbo to --triple-pbo) are slower. Is this expected? I've thought that the pbo versions

Re: [osg-users] osgscreencapture transfer speeds (PBOs slower)

2009-12-07 Thread Robert Osfield
Hi J.P, I found that the GL driver support for properly accelerating the reading from the GPU memory using PBO to be very sensitive for pixel format, and if you fell off the past path it would indeed be slower. It's a while since I implemented osgscreencapture so can't remember all the details

Re: [osg-users] osgscreencapture transfer speeds (PBOs slower)

2009-12-07 Thread J.P. Delport
Hi Robert, Robert Osfield wrote: Hi J.P, I found that the GL driver support for properly accelerating the reading from the GPU memory using PBO to be very sensitive for pixel format, and if you fell off the past path it would indeed be slower. It's a while since I implemented osgscreencapture

Re: [osg-users] osgscreencapture transfer speeds (PBOs slower)

2009-12-07 Thread Art Tevs
Hi J.P. , Robert, as far as I remember PBO is indeed slower for formats not natively supported by the VRAM. On nVidia GPU's it seems that the PBO transfer of GL_BGRA is imho the fastest one. Yes, it is even faster than GL_RGBA. I think that has something todo with alignment of the data in the

Re: [osg-users] osgscreencapture transfer speeds (PBOs slower)

2009-12-07 Thread Art Tevs
Hi J.P. I think one can get more thatn 1GB/s. Of course it strongly depends on used system memory, motherboard and CPU. There was discussion on GPGPU forum (http://www.gpgpu.org/forums/viewtopic.php?t=4798). And it seems that it is also a matter of how to write the correct benchmark. So,