[RFC wayland] protocol: Add wl_surface.buffer_damage

Fri Nov 6 12:55:57 PST 2015

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>
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>
> 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>
> > ---
> >
> > 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
> >
> > _______________________________________________
> > wayland-devel mailing list
> > wayland-devel at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>
>
>
> --
>   Jasper
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>
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