surface buffer cardinality and outputs

[Jerome Glisse]

On Thu, Mar 14, 2013 at 3:38 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> On Wed, 13 Mar 2013 19:52:55 +0100
> Sylvain BERTRAND <sylware at legeek.net> wrote:
>
>> The other option would be to ignore those output properties, and
>> the compositor would manage something with an output agnostic
>> buffer.  In that case, we would remove the subpixel property from
>> the output to stay consistent (mode is used for shell surface
>> fullscreen).
>
> Btw. the sub-pixel property has also other issues: if the compositor
> does any surface transformations instead of pure translation, any
> sub-pixel rendering will become incorrect. That's a gap we haven't
> really tried to solve yet, either.
>
>
> Thanks,
> pq

Sorry for jumping kind of late in the discussion. I think client
should provide a dpi information with their surface telling the
compositor for which dpi the surface was rendered for an allow
compositor to upscale surface for higher dpi. That way application
that care about dpi could do proper rendering while thing that can be
upscale through overlay or other means are upscale (many thing on a
desktop can't be rerendered in higher dpi video, picture, ...). This
dpi property should be per sub-surface so an application can have
sub-surface with different dpi, think something like a browser with
text in high dpi and embedded video in original size.

For sub-pixel rendering the solution i have been thinking for a while
but still haven't had time to prototype on weston, is to have weston
send the transformation matrix to the client have the client render in
screen coordinate space and when commiting its surface the client
would also tell which transformation matrix it did use. Again this
should be per sub-surface so that one can render the text and ui in
screen space and do proper anti-aliasing while just do nothing for
picture or video and let the compositor do the transformation. This is
i believe the cleanest solution for proper sub-pixel rendering inside
wayland paradigm.

Cheers,
Jerome