[cairo] cairo on cross-endian architectures
Egon.Nijns at bib.kuleuven.be
Mon Sep 12 03:17:05 PDT 2005
I'm running into some color problems (red and blue are swapped) with
cairo (as used by Mozilla's SVG implementation) on a cross-endian
architecture (these were already discussed earlier on the cairo mailing
list, I've attached part of the earlier discussion below).
We are using a Sun Ray Server, and I think that this is a cross-endian
architecture, since I'm seeing the swapped colors problem. I've
submitted a badly written patch doing the byte-swaps Owen Taylor
suggested to Mozilla's bugzilla, and want to clean up the code (I hope
that a fix for this can one day be included in cairo).
The biggest problem I have is that I don't know how to do the
cross-endian detection (plus I have no experience with Xlib coding
whatsoever), but maybe someone on this list can give me some clues on
how to do this properly?
> On Tue, 2005-05-10 at 15:04 -0600, Peter Dennis Bartok wrote:
>>> Hi all,
>>> Has anyone successfully used Cairo on anything other than a
>>> Xfree/Xorg X server?
>>> Two cases where we are seeing problems are Sun's X server and
>>> Hummingbirds' Exceed Win32 X server. On both or applications usually
>>> die with a BadMatch (in XPutImage or XGetImage). *Also, on Servers
>>> that have MSB first, cairo treats it as if they are LSB first,
>>> thereby swapping red and blue.*
>>> My understanding of the inner workings of cairo and libpixman sadly
>>> is quite limited, so I wouldn't know where to start trying to fix this.
> No libpixman or Cairo knowledge needed. It's all really shallow inside
> *For the endianess problems, the code simply needs to byte-swap the
> image after calling XGetImage / before calling XPutImage if you detect
> cross-endian. (Image byte order not equal to local byte
> (In some cases, there are tricks you can play with calling a big
> endian RGB x888 visual a little endian BGR 888x visual. libpixman can
> draw to a BGR 888x visual but it's going to be slow. Certainly simpler
> to just byte-swap than to worry about
> accelerating that.)
> It looks to me like the code should work fine on MSB as long
> as the client/server endianess matches.
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