[Mesa-stable] [Mesa-dev] [PATCH v2 2/2] mesa: _mesa_format_convert should be endian agnostic

[Matt Turner]

On Fri, Aug 7, 2015 at 12:24 PM, Oded Gabbay <oded.gabbay at gmail.com> wrote:
> This patch fixes a bug that is manifested in the read path of mesa when
> running on big-endian machines. The effects can be seen when running
> piglit sanity test and/or taking a screen capture.
>
> The bug is caused when _mesa_format_convert receives src_format as
> mesa_format, which it thens changes to mesa_array_format. During this
> change, it checks for endianness and swaps the bytes accordingly.
> However, because the bytes are _already_ swapped in the memory itself
> (being written there by llvmpipe/softpipe/sw rast), and src_format
> value matches the _actual_ contents of the memory, the result of the
> read is wrong.
>
> Therefore, because other layers/functions, such as llvm or
> read_rgba_pixels() takes care whether we are dealing with big-endian or
> little-endian, _mesa_format_convert should be endian agnostic to avoid
> duplicate swapping of bytes.
>
> btw, it is also mentioned in the comment of the function that it doesn't
> handle byte-swapping, so the original code contradicts the documentation.
>
> Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>
> CC: "10.5 10.6" <mesa-stable at lists.freedesktop.org>
> Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>

Multiple S-o-b. Whoops. Just fix before committing. :)