[Pixman] Pixman on iOS

[Siarhei Siamashka]

On Sun, Mar 6, 2011 at 5:28 AM, cu <cairouser at yahoo.com> wrote:
> I am starting to look (very carefully) into building pixman and, one day
> may be, cairo on iphone/ipad/iOS.
>
> So far I've got to the point where I can configure and build pixman for
> a single arm architecture. So far so good.

> However, I seem to be unable to enable NEON optimizations. Presumably,
> iPhone/iPad armv7 does have those.
>
> I wonder if the issue is specific set of compiler directives used to
> access NEON operations? Any help or insight would be appreciated.

In order to compile NEON assembly optimizations, ideally one would
need GAS compatible assembler (fully supporting 'modern' features like
macros) which can produce Mach-O object files. I'm not aware of the
latest news on this front and my information may be a bit outdated.
But from what I read, apparently Apple forked an ancient version of
binutils ages ago and has a very primitive assembler. And on the other
hand, upstream GNU binutils do not support Mach-O yet. The popular
solution seems to be to use intermediate preprocessors written in
scripting languages on assembly source files to produce something that
can be digested by the assembler from iPhone SDK.

After NEON assembly can be compiled, pixman runtime CPU detection
needs to be tweaked to detect NEON and enable it on iPhone. And
finally, somebody needs to check whether iPhone ABI is compatible with
what is used by Linux and Android (ARM EABI) because this can be
potentially a source of really bad runtime bugs. Just running tests
from pixman test suite to see whether they pass or fail may be a good
start.

That said, I neither have any Apple hardware required to do iPhone
development, nor do I feel that it would be the right thing for me to
work on this issue considering many factors. Surely it would have been
better for everyone if Apple tried to be more compatible with Linux.
But as it does not seem to be the case, somebody has to do some work
to make sure that pixman NEON optimizations work there.

-- 
Best regards,
Siarhei Siamashka