Re: xaa vs. WriteImage()

[Michael Lorenz]

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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  
<[EMAIL PROTECTED]> wrote:
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 Hello,

 On Mar 5, 2008, at 19:06, Alex Deucher wrote:

On Tue, Mar 4, 2008 at 5:34 PM, Michael Lorenz
<[EMAIL PROTECTED]> wrote:
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 Hello,


On Mar 4, 2008, at 15:37, Marc Aurele La France wrote:

On Mon, 3 Mar 2008, Michael Lorenz wrote:

I noticed the following - XAACopyArea() only attempts to use
accelerated WriteImage() when writing to a DRAWABLE_WINDOW but  
not
on off-screen pixmaps. I used the following changes to make it
work:

diff -u -w -r1.1.1.3 xaaCpyArea.c
- --- xaaCpyArea.c   9 Jun 2001 15:09:02 -0000       1.1.1.3
+++ xaaCpyArea.c     3 Mar 2008 20:51:05 -0000
@@ -64,9 +64,16 @@
           return (XAABitBlt( pSrcDrawable, pDstDrawable,
             pGC, srcx, srcy, width, height, dstx, dsty,
             XAADoBitBlt, 0L));
+    } else {
+        if(infoRec->ScreenToScreenBitBlt &&
+         CHECK_ROP(pGC,infoRec->ScreenToScreenBitBltFlags) &&
+         CHECK_ROPSRC(pGC,infoRec->ScreenToScreenBitBltFlags) &&
+         CHECK_PLANEMASK(pGC,infoRec- 
>ScreenToScreenBitBltFlags))
+            return (XAABitBlt( pSrcDrawable, pDstDrawable,
+            pGC, srcx, srcy, width, height, dstx, dsty,
+            XAADoImageWrite, 0L));
     }
   }

This does not look correct.  Shouldn't this be more in line with
the case where the destination drawable is a window?  (i.e. test
bitsPerPixel's and WritePixmap files instead of
ScreenToScreenBitBlt).

 The whole logic looks a little bit fishy, I used the first if()'s
 source-in-memory branch first but wasn't quite sure if that's  
doing
 the right thing, where it;s now looked better to me but I won't
claim
 I completely understand XAA's inner voodoo. All I want is the make
 XAA use ImageWrite()s for all RAM-to-VRAM transfers if the driver
 supports it.
 Otherwise, teaching the framebuffer layer to cope with a tiled
 framebuffer might be necessary in the long run, any pointers
where to
 start?

Several drivers (radeon, intel, savage) in the Xorg tree provide
support for various tiling methods.  Generally the chip provides a
surface control or aperture for exposing a tiled region to the  
CPU as
a linear surface.  For acceleration, you have to keep track of what
buffers are tiled in the driver and do the right thing with the
blitter when using those surfaces.

 Yeah, I'm dimly aware of these things - my problem is that the
 hardware in question doesn't give me a linear view on the  
framebuffer.
 All I have is a small linear buffer I can use to DMA data in or out
 of the tiled framebuffer. The other problem is that the machine's
 native pixel format is RGBA, if I want 24bit colour that's the only
 one I can use. Fortunately the DMA engine can convert pixels on the
 fly so I can pretend it's ABGR. So pixels would have to be endian-
 flipped as well when the fb layer accesses VRAM - is there any prior
 art for that?

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.

have fun
Michael
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