On Fri, Apr 6, 2018 at 12:01 PM, Michel Dänzer <mic...@daenzer.net> wrote:
> On 2018-03-27 07:53 PM, Daniel Stone wrote:
>> On 12 March 2018 at 20:45, Mario Kleiner <mario.kleiner...@gmail.com> wrote:
>>> We need to distinguish if a backing pixmap of a window is
>>> XRGB2101010 or XBGR2101010, as different gpu hw supports
>>> different formats. NVidia hw prefers XBGR, whereas AMD and
>>> Intel are happy with XRGB.
>>>
>>> We use the red channel mask of the visual to distinguish at
>>> depth 30, but because we can't easily get the associated
>>> visual of a Pixmap, we use the visual of the x-screens root
>>> window instead as a proxy.
>>>
>>> This fixes desktop composition of color depth 30 windows
>>> when the X11 compositor uses EGL.
>>
>> I have no reason to doubt your testing, so this patch is:
>> Acked-by: Daniel Stone <dani...@collabora.com>
>>
>> But it does rather fill me with trepidation, given that X11 Pixmaps
>> are supposed to be a dumb 'bag of bits', doing nothing else than
>> providing the same number and size of channels to the actual client
>> data for the Visual associated with the Window.
>
> As far as X11 is concerned, the number of channels and their sizes don't
> even matter; a pixmap is simply a container for an unsigned integer of n
> bits (where n is the pixmap depth) per pixel, with no inherent meaning
> attached to those values.
>
> That said, I'm not sure this is true for EGL as well. But even if it
> isn't, there would have to be another mechanism to determine the format,
> e.g. a config associated with the EGL pixmap. The pixmap doesn't even
> necessarily have the same depth as the root window, so using the
> latter's visual doesn't make much sense.
>

Hi Michel. I thought with this patch i was implementing what you
proposed earlier as a heuristic on how to get around the "pixmaps
don't have an inherent format, only a depth" problem?

My (possibly inaccurate) understanding is that one can only create a
depth 30 pixmap if the x-screen runs at depth >= 30. It only exposes
depth 30 as supported pixmap format (xdpyinfo) if xorg.conf
DefaultDepth 30 is selected, whereas other depths like
1,4,8,15,16,24,32 are always supported at default depth 24. Iff depth
30 is selected, then the root window has depth 30, and a depth 30
visual. If each driver only exports one channel ordering for depth 30,
then the channel ordering of any pixmaps associated drawable should be
the same as the one of the root window.

Wrong thinking?
-mario


>
> --
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer
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