[PATCH 00/15] weston scaling support

[John Kåre Alsaker]

On Tue, May 28, 2013 at 3:40 PM, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> On Tue, 28 May 2013 15:10:53 +0200
> John Kåre Alsaker <john.kare.alsaker at gmail.com> wrote:
>
> > On Thu, May 23, 2013 at 2:57 AM, Kristian Høgsberg <hoegsberg at gmail.com
> >wrote:
> >
> > > I read through the latest wayland protocol patches and the discussion
> > > around them and didn't seen anything I didn't like.  I think the
> > > approach here is good and agree with the consensus.  This patch series
> > > looks great too and I like the improvements to the pixman renderer and
> > > the compositor-x11.c optimization.
> > >
> > Where did the consensus come from?
> >
> > I think the lack of fractional scale factors will result in further
> > extensions to support that in the future. I really also dislike how this
> > implementation won't allow clients to draw with pixel precision on
> scaling
> > factors above 1.
>
> Quite the contrary, it does allow drawing at least at pel precision, and
> it even guarantees that a pel always accurately hits the pixel
> boundaries in both the buffer, and all outputs regardless of their
> scale factor (provided the compositor does not do additional
> transformations of its own).
>
The only problem is that pel precision is not pixel precision. Furthermore
output sizes are not aligned with pel unit sizes, they are in pixels.


> Introduce rational factors, and it can only be of worse image quality,
> combined with a lot of protocol and interpretation difficulties, when
> sizes are suddenly not integers.
>
Which protocol and interpretation difficulties are you referring to? I've
not found any in my proposal, buffer and surface sizes are still in
integers there.
I do wonder what happens if you attach a buffer of size 101x101 in the
current implementation with a scale factor of two. Is the compositor
expected to use 50.5x50.5 as the surface size?

While rendering at rational factor can't be of better quality, it can
however be done at a much higher quality than downscaling, faster and with
less memory usage.

>
> If you really need an output scaling factor like 1.5, then you report it
> as either 1 or 2, and do a compensating scaling in the compositor to
> achieve 1.5. That is the best compromize I can imagine, since to be
> honest, 1.5 does not work for the protocol nor the clients' rendering.
>
1.5 works just fine for the protocol and clients' rendering.


> I thought I explained that before, maybe to someone else, but on this
> mailing list anyway.
>
>
> - pq
>
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