[RFC wayland] protocol: Add wl_surface.buffer_damage
Derek Foreman
derekf at osg.samsung.com
Thu Nov 12 11:27:34 PST 2015
There seems to be some heated debate about whether we should deprecate
the old request or not, and how aggressively we should push people
towards the new one.
I've stayed out of that conversation, and think if we want to consider
that we can still do so after we land the new buffer_damage (now to be
called damage_pixels?) request, with a weston implementation, and
perhaps patch mesa to use it.
We'll want the new request either way, the deprecation or defamation of
the old request can be a follow up. :)
On 06/11/15 02:55 PM, Bill Spitzak wrote:
> The description for wl_surface.damage should be shortened to a minimal
> indication that this is for back-compatibility only and that refer to
> the buffer_damage request. Something like "identical to buffer_damage if
> the buffer and surface coordinates are equal, otherwise the behaviour is
> undefined".
>
> On Fri, Nov 6, 2015 at 11:08 AM, Jasper St. Pierre
> <jstpierre at mecheye.net <mailto:jstpierre at mecheye.net>> wrote:
>
> To help clear things up, I think we should deprecate the
> wl_surface.damage request and document that the coordinates are
> effectively undefined -- for legacy reasons, if you see
> wl_surface.damage, it should be considered a damage for the entire
> surface.
>
> On Fri, Nov 6, 2015 at 10:55 AM, Derek Foreman
> <derekf at osg.samsung.com <mailto:derekf at osg.samsung.com>> 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.buffer_damage 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.buffer_damage request
> > was another option.
> >
> > Signed-off-by: Derek Foreman <derekf at osg.samsung.com
> <mailto:derekf at osg.samsung.com>>
> > ---
> >
> > Necro-posting on:
> >
> http://lists.freedesktop.org/archives/wayland-devel/2014-February/013440.html
> > and
> >
> http://lists.freedesktop.org/archives/wayland-devel/2014-February/013442.html
> >
> > This came up on IRC again the other day, and it's still an
> unsolved problem...
> > I'm posting this as RFC to see if anyone's interested in it - I'll
> do an
> > implementation if we can get an agreement on the protocol text.
> >
> > protocol/wayland.xml | 44
> ++++++++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 42 insertions(+), 2 deletions(-)
> >
> > diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> > index 9c22d45..1cb2f66 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.
> > @@ -1327,6 +1327,46 @@
> > </description>
> > <arg name="scale" type="int"/>
> > </request>
> > +
> > + <!-- Version 4 additions -->
> > + <request name="buffer_damage" 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 pending
> buffer
> > + must be set by wl_surface.attach before sending damage. 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 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. This is desirable because EGL implementations
> > + are unaware of buffer scale and buffer transform and can only
> > + provide damage in buffer co-ordinates. Damage in buffer
> > + co-ordinates is required for EGLSwapBuffersWithDamage to work
> > + efficiently.
> > +
> > + Mixing wl_surface.buffer_damage and wl_surface.damage requests
> > + on the same surface will result in undefined behaviour.
> > + </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">
> > --
> > 2.6.1
> >
> > _______________________________________________
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>
>
>
> --
> Jasper
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