Re: xaa vs. WriteImage()

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Hello,

On Mar 6, 2008, at 18:02, Alex Deucher wrote:

On Thu, Mar 6, 2008 at 5:17 PM, Michael Lorenz <macallan@xxxxxxxxxx> wrote:
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 Hello,

 On Mar 6, 2008, at 16:40, Alex Deucher wrote:

On Thu, Mar 6, 2008 at 4:26 PM, Michael Lorenz
<macallan@xxxxxxxxxx> wrote:
On Mar 6, 2008, at 15:58, Alex Deucher wrote:

On Thu, Mar 6, 2008 at 2:58 PM, Michael Lorenz
<macallan@xxxxxxxxxx> wrote:
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 Hello,

 On Mar 6, 2008, at 14:12, Alex Deucher wrote:

On Thu, Mar 6, 2008 at 2:00 PM, Michael Lorenz
EXA has prepare/finish access hooks for CPU access to buffers. I don't think XAA has anything similar. There's also an wrapable FB
module, although I think it's only available in Xorg.

 I'll have a look at that - the main reason I'm using XFree86 is
that
it's already working on NetBSD/sgimips, Xorg needs some more work
but
 I'll eventually do it.
Hmm, some drivers access video memory through tiny apertures like
the
 VGA range - maybe I can do something like this - let the rest
of the
 Xserver render into my DMA buffer and then blit it in place.

Use shadowfb and hook in a custom shadowupdate() function.

 Wouldn't that interfere with XAA? If I could catch the framebuffer
 writes that bypass XAA that way that would solve my problem.
 Thanks!

Yeah, you gotta pick one or the other IIRC.  However for most modern
desktops you either have to be entirely SW or entirely HW or
performance sucks.  You lose if any sort of fallbacks cause a pixmap
migration to/from vram.

 In my case VRAM is RAM, and the CPU is pretty slow - I've had things
running entirely SW and performance sucked. Not the slowest I've ever
 seen but nowhere near what the HW can do.
 Also, many X applications have trouble with the HW's native pixel
 format, cairo for instance just crashes. Using the DMA engine I can
 pretend it's using something more common - ABGR - and those
 applications just work fine. I think the next thing I'll try is to
 pretend that we're accessing VRAM through a small window, there must
 be prior art for that somewhere in the source tree.


the sgi impact driver I mentioned before
(http://cgit.freedesktop.org/xorg/driver/xf86-video-impact/) does
that.  IIRC, there's no way to access the vram directly so everything
gets sent to the card via dma.

Yeah, that's the software-only case. Interesting but I'd rather find a way to make this work while being able to use the rendering engine.

have fun
Michael
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