On Thu, 5 Sep 2002, Michel Lanners wrote:
> On 4 Sep, this message from Mark Vojkovich echoed through cyberspace:
> >> Is there any way to grab a screenshot really fast. I mean like a 1280x1024
> >> 32bbp screenshot in a couple of milliseconds? I am using XShmGetImage()
> >> right now, but a screenshot of the size mentioned above takes about 110 to
> >> 120 milliseconds. Doing the math this gives me a bandwidth of about 40 to
> >> 45 MB/s. Surely there must be a faster way of doing it.
> >>
> >> The system i am sitting on is a Linux box, XFree 4.2.0, nVidia graphics
> >> (GF2) with the nVidia binary driver.
> >>
> > No, there's not a way to copy quickly from the framebuffer.
> > Reads across AGP are limited to PCI bandwidth. I am seeing over
> > 100 MB/sec in general though (closer to 150 MB/sec on fast P4s).
>
> Would there be a way to use the graphic chip's blitter to copy the
> framebuffer contents over AGP to main memory?
No, AGP is for system ram -> video card transfers only.
What might be possible is to reserve space in video ram, blit the
framebuffer contents there and then slowly transfer them to main ram at
your convenience.
Also, using DMA will speedup things, as plain reads can be very slow.
Vladimir Dergachev
>
> Cheers
>
> Michel
>
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> Michel Lanners | " Read Philosophy. Study Art.
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