willie at zeitgeistmedia.net
Tue Apr 25 12:51:31 CDT 2006
Am Dienstag, 25. April 2006 19:20 schrieb Stefan Dösinger:
> > AFAIK, there are four targets OpenGL can draw to on X: X windows,
> > Pbuffers, FBOs or GLX pixmaps. EXT_framebuffer_object should be the most
> > interesting approach, as it's supposed to somewhat similar to Pbuffer
> > rendering, but supposed to be more portable and faster:
> > "This extension defines a simple interface for drawing to rendering
> > destinations other than the buffers provided to the GL by the
> > window-system."
> > But I guess a FBO or a GLX pixmap would still introduce a similar
> > performance hit compared to Pbuffer rendering?
> FBOs are very interesting for this, but the mail performance issue is to
> read back from the video card. Video cards are mainly output devices,
> reading from them is slow. AFAIK the driver even has to use PCI transfers
> for that, because AGP isn't designed for reading back data. I could be
> wrong with this, and I don't know how PCIe affects this.
Probably got something wrong, but FBOs are supposed to be very fast, exactly
because you _don't_ have to read the data back? It also needs no context
switches, and it's supposed to work on pretty much all graphic cards, even
very old ones.
Here's a small presentation by Simon Green/ Nvidia, including comparison
between FBOs, Pbuffers and WGL_ARB_render_to_texture:
And a small overview, also by Simon Green:
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<willie at froq.net>
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