[PATCH wayland v4] protocol: Add wl_surface.damage_buffer
Pekka Paalanen
ppaalanen at gmail.com
Sun Nov 29 23:51:37 PST 2015
On Fri, 27 Nov 2015 09:33:41 -0800
Jason Ekstrand <jason at jlekstrand.net> wrote:
> On Nov 27, 2015 1:35 AM, "Pekka Paalanen" <ppaalanen at gmail.com> wrote:
> >
> > On Fri, 27 Nov 2015 16:47:19 +0800
> > Jonas Ådahl <jadahl at gmail.com> wrote:
> >
> > > On Thu, Nov 26, 2015 at 03:44:12PM -0600, Derek Foreman wrote:
> > > > wl_surface.damage uses surface local co-ordinates.
> > > >
> > > > Buffer scale and buffer transforms came along, and EGL surfaces
> > > > have no understanding of them.
> > > >
> > > > Theoretically, clients pass damage rectangles - in Y-inverted surface
> > > > co-ordinates) to EGLSwapBuffersWithDamage, and the EGL implementation
> > > > passed them on to wayland. However, for this to work the EGL
> > > > implementation must be able to flip those rectangles into the space
> > > > the compositor is expecting, but it's unable to do so because it
> > > > doesn't know the height of the transformed buffer.
> > > >
> > > > So, currently, EGLSwapBuffersWithDamage is unusable and EGLSwapBuffers
> > > > has to pass (0,0) - (INT32_MAX, INT32_MAX) damage to function.
> > > >
> > > > wl_surface.damage_buffer allows damage to be registered on a surface
> > > > in buffer co-ordinates, avoiding this problem.
> > > >
> > > > Credit where it's due, these ideas are not entirely my own:
> > > > Over a year ago the idea of changing damage co-ordinates to buffer
> > > > co-ordinates was suggested (by Jason Ekstrand), and it was at least
> > > > partially rejected and abandoned. At the time it was also suggested
> > > > (by Pekka Paalanen) that adding a new wl_surface.damage_buffer request
> > > > was another option.
> > > >
> > > > This will eventually resolve:
> > > > https://bugs.freedesktop.org/show_bug.cgi?id=78190
> > > > by making the problem irrelevant.
> > > >
> > > > Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
> > >
> > > Reviewed-by: Jonas Ådahl <jadahl at gmail.com>, with a couple of comments
> > > below.
> >
> > Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> >
> > ...
> >
> > > > ---
> > > >
> > > > Changes from v3:
> > > > replaced the last paragraph with Pekka's version
> > > > (with one tiny grammar change)
> > > >
> > > > protocol/wayland.xml | 49
> +++++++++++++++++++++++++++++++++++++++++++++++--
> > > > 1 file changed, 47 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> > > > index f9e6d76..4e97bb9 100644
> > > > --- a/protocol/wayland.xml
> > > > +++ b/protocol/wayland.xml
> > > > @@ -176,7 +176,7 @@
> > > > </event>
> > > > </interface>
> > > >
> > > > - <interface name="wl_compositor" version="3">
> > > > + <interface name="wl_compositor" version="4">
> > > > <description summary="the compositor singleton">
> > > > A compositor. This object is a singleton global. The
> > > > compositor is in charge of combining the contents of multiple
> > > > @@ -986,7 +986,7 @@
> > > > </event>
> > > > </interface>
> > > >
> > > > - <interface name="wl_surface" version="3">
> > > > + <interface name="wl_surface" version="4">
> > > > <description summary="an onscreen surface">
> > > > A surface is a rectangular area that is displayed on the
> screen.
> > > > It has a location, size and pixel contents.
> > > > @@ -1109,6 +1109,10 @@
> > > > wl_surface.commit assigns pending damage as the current damage,
> > > > and clears pending damage. The server will clear the current
> > > > damage as it repaints the surface.
> > > > +
> > > > + Alternatively, damage can be posted with wl_surface.damage_buffer
> > > > + which uses buffer co-ordinates instead of surface co-ordinates,
> > > > + and is probably the preferred and intuitive way of doing this.
> > > > </description>
> > > >
> > > > <arg name="x" type="int"/>
> > > > @@ -1325,6 +1329,47 @@
> > > > </description>
> > > > <arg name="scale" type="int"/>
> > > > </request>
> > > > +
> > > > + <!-- Version 4 additions -->
> > >
> > > Bikeshed mode enabled: missing empty line between "Version N additions"
> > > and actual additions.
> > >
> > > > + <request name="damage_buffer" since="4">
> > > > + <description summary="mark part of the surface damaged using
> buffer co-ordinates">
> > > > + This request is used to describe the regions where the pending
> > > > + buffer is different from the current surface contents, and where
> > > > + the surface therefore needs to be repainted. The compositor
> > > > + ignores the parts of the damage that fall outside of the surface.
> > > > +
> > > > + Damage is double-buffered state, see wl_surface.commit.
> > > > +
> > > > + The damage rectangle is specified in buffer coordinates.
> > > > +
> > > > + The initial value for pending damage is empty: no damage.
> > > > + wl_surface.damage_buffer adds pending damage: the new pending
> > > > + damage is the union of old pending damage and the given rectangle.
> > > > +
> > > > + wl_surface.commit assigns pending damage as the current damage,
> > > > + and clears pending damage. The server will clear the current
> > > > + damage as it repaints the surface.
> > > > +
> > > > + This request differs from wl_surface.damage in only one way - it
> > > > + takes damage in buffer co-ordinates instead of surface local
> > > > + co-ordinates. While this generally is more intuitive than surface
> > > > + co-ordinates, it is especially desirable when using wp_viewport
> > > > + or when a drawing library (like EGL) is unaware of buffer scale
> > > > + and buffer transform.
> > > > +
> > > > + Since it is impossible to convert between buffer and surface
> > > > + co-ordinates until all the possible parameters affecting the
> > > > + surface size and the buffer-surface mapping are known at
> > > > + wl_surface.commit time, damage from wl_surface.damage and
> > > > + wl_surface.damage_buffer must be accumulated separately in a
> > > > + compositor and combined during wl_surface.commit at the earliest.
> > >
> > > As Jason already pointed out, this looks out of place. With some
> > > imagination, it might also not entirely true. A compositor may put
> > > damage "together" in a single list, with "transform this way" flags next
> > > to regions in different coordinate spaces, and then later process and
> > > combine at commit when all information is available. Sure, it makes
> > > little sense to do things this way, but it wouldn't be wrong while
> > > still, depending on how interpreted, not really doing what the above
> > > paragraph said.
> >
> > Yeah. It's implementation guideline for compositor writers. Maybe it
> > should have started by stating that, so that client writers don't get
> > confused.
> >
> > I suppose we all agree that in lack of better wording for the moment,
> > this is good to land. If someone comes up with a better wording, we can
> > patch that later.
>
> How about something like this:
>
> Note: Because buffer transformation changes and damage requests may be
> interleaved in the protocol stream, It is impossible to determine the
> actual mapping between surface and buffer damage until wl_surface.commit
> time. Therefore, compositors wishing to take both kinds of damage into
> account will have to accumulate damage from the two requests separately and
> only transform from one to the other after receiving the wl_surface.attach.
wl_surface.commit, not attach.
> That says more or less the same thing but puts the focus on the protocol
> rather than implantation. It also leaves open the possibility of different
> compositor implementations that don't bother trying to combine the two.
With the above typo fix, sounds good to me. :-)
Thanks,
pq
>
> --Jason
>
> > I restored a couple of CCs, and since 26th was thanksgiving in the US,
> > maybe this should land early next week if no-one objects.
> >
> >
> > Thanks,
> > pq
> >
> > > > + </description>
> > > > +
> > > > + <arg name="x" type="int"/>
> > > > + <arg name="y" type="int"/>
> > > > + <arg name="width" type="int"/>
> > > > + <arg name="height" type="int"/>
> > > > + </request>
> > > > </interface>
> > > >
> > > > <interface name="wl_seat" version="5">
> > > > --
> > > > 2.6.2
> > > >
> > > > _______________________________________________
> > > > wayland-devel mailing list
> > > > wayland-devel at lists.freedesktop.org
> > > > http://lists.freedesktop.org/mailman/listinfo/wayland-devel
> >
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