[PATCH wayland-protocols v2] Add alpha-compositing protocol

[Scott Anderson]

This protocol specifies a set of interfaces used to control the alpha
compositing and blending of surface contents.

It's based on the Chromium Wayland protocol of the same name ([1]) and
an old proposal of this protocol ([2]).

Differences from v1 proposal:
- Add additional "fromsource" blending equation used by [3]
- Allow the server to advertise which blending equations it supports
- Added a protocol errors for using an unsupported equation
- Added a protocol error for using an invalid alpha value
- Added clarification about wl_surface.set_opaque_region
- Added clarification about per-pixel alpha values

A proof-of-concept implementation for Weston can be found at:
https://gitlab.freedesktop.org/ascent/weston/tree/alpha-compositing-v1

[1] https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
[2] https://lists.freedesktop.org/archives/wayland-devel/2017-August/034741.html
[3] https://lists.freedesktop.org/archives/wayland-devel/2018-September/039437.html
---
Makefile.am | 1 +
unstable/alpha-compositing/README | 5 +
.../alpha-compositing-unstable-v1.xml | 172 ++++++++++++++++++
3 files changed, 178 insertions(+)
create mode 100644 unstable/alpha-compositing/README
create mode 100644 unstable/alpha-compositing/alpha-compositing-unstable-v1.xml

diff --git a/Makefile.am b/Makefile.am
index 6394e26..ac6c9f8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -21,6 +21,7 @@ unstable_protocols = \
unstable/xdg-output/xdg-output-unstable-v1.xml \
unstable/input-timestamps/input-timestamps-unstable-v1.xml \
unstable/xdg-decoration/xdg-decoration-unstable-v1.xml \
+ unstable/alpha-compositing/alpha-compositing-unstable-v1.xml \
$(NULL)

stable_protocols = \
diff --git a/unstable/alpha-compositing/README b/unstable/alpha-compositing/README
new file mode 100644
index 0000000..5826967
--- /dev/null
+++ b/unstable/alpha-compositing/README
@@ -0,0 +1,5 @@
+Alpha compositing protocol
+
+Maintainers:
+David Reveman <***@chromium.org>
+Alexandros Frantzis <***@collabora.com>
diff --git a/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml b/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
new file mode 100644
index 0000000..aae1d6e
--- /dev/null
+++ b/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
@@ -0,0 +1,172 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="alpha_compositing_unstable_v1">
+
+ <copyright>
+ Copyright 2016 The Chromium Authors.
+ Copyright 2017-2018 Collabora Ltd
+ Copyright 2018 NXP
+
+ Permission is hereby granted, free of charge, to any person obtaining a
+ copy of this software and associated documentation files (the "Software"),
+ to deal in the Software without restriction, including without limitation
+ the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ and/or sell copies of the Software, and to permit persons to whom the
+ Software is furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice (including the next
+ paragraph) shall be included in all copies or substantial portions of the
+ Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ DEALINGS IN THE SOFTWARE.
+ </copyright>
+
+ <description summary="Protocol for more advanced compositing and blending">
+ This protocol specifies a set of interfaces used to control the alpha
+ compositing and blending of surface contents.
+
+ Warning! The protocol described in this file is experimental and backward
+ incompatible changes may be made. Backward compatible changes may be added
+ together with the corresponding interface version bump. Backward
+ incompatible changes are done by bumping the version number in the protocol
+ and interface names and resetting the interface version. Once the protocol
+ is to be declared stable, the 'z' prefix and the version number in the
+ protocol and interface names are removed and the interface version number is
+ reset.
+ </description>
+
+ <interface name="zwp_alpha_compositing_v1" version="1">
+ <description summary="alpha_compositing">
+ The global interface exposing compositing and blending capabilities is
+ used to instantiate an interface extension for a wl_surface object.
+ This extended interface will then allow the client to specify the
+ blending equation and alpha value used for compositing the wl_surface.
+ </description>
+
+ <enum name="error">
+ <entry name="blending_exists" value="0"
+ summary="the surface already has a blending object associated"/>
+ </enum>
+
+ <request name="destroy" type="destructor">
+ <description summary="unbind from the blending interface">
+ Informs the server that the client will not be using this
+ protocol object anymore. This does not affect any other objects,
+ blending objects included.
+ </description>
+ </request>
+
+ <request name="get_blending">
+ <description summary="extend surface interface for blending">
+ Instantiate an interface extension for the given wl_surface to
+ provide surface blending. If the given wl_surface already has
+ a blending object associated, the BLENDING_EXISTS protocol error
+ is raised.
+ </description>
+
+ <arg name="id" type="new_id" interface="zwp_blending_v1"
+ summary="the new blending interface id"/>
+ <arg name="surface" type="object" interface="wl_surface"
+ summary="the surface"/>
+ </request>
+
+ <event name="blending">
+ <description summary="supported blending equations">
+ This event advertistes the blending equations that the server
+ supports. All the supported blending equations are advertised once
+ when the client binds to this interface. A roundtrip after binding
+ gurantees that the client has received all supported blending
+ equations.
+
+ For the definition of the blending equations, see the
+ zwp_blending_v1.blending_equation enum.
+
+ The server must always advertise the 'none' blending equation.
+ </description>
+ <arg name="equation" type="uint" summary="the blending equation"/>
+ </event>
+ </interface>
+
+ <interface name="zwp_blending_v1" version="1">
+ <description summary="blending interface to a wl_surface">
+ An additional interface to a wl_surface object, which allows the
+ client to specify the blending equation used for compositing and
+ an alpha value applied to the whole surface.
+
+ When the blending object is created its blending equation is
+ 'none' and its alpha is 1.0, i.e., it's inactive by default. Clients
+ can activate it by setting the blending equation and alpha value.
+
+ Use of this interface has no effect on the surface's opaque region
+ as set by wl_surface.set_opaque_region. Clients must make sure to set
+ their opaque region correctly to prevent repaint artifacts.
+
+ If the wl_surface associated with the blending object is destroyed,
+ the blending object becomes inert.
+
+ If the blending object is destroyed, the blending state is removed
+ from the wl_surface. The change will be applied on the next
+ wl_surface.commit.
+ </description>
+
+ <enum name="blending_equation">
+ <description summary="different blending equations for compositing">
+ Blending equations that can be used when compositing a surface.
+ </description>
+ <entry name="none" value="0" summary="blending object is inactive"/>
+ <entry name="opaque" value="1" summary="(one, zero)"/>
+ <entry name="premultiplied" value="2" summary="(one, one_minus_src_alpha)"/>
+ <entry name="straight" value="3" summary="(src_alpha, one_minus_src_alpha)"/>
+ <entry name="fromsource" value="4" summary="(src_alpha, src_alpha)"/>
+ </enum>
+
+ <enum name="error">
+ <entry name="invalid_equation" value="0"
+ summary="the blending equation is not supported"/>
+ <entry name="invalid_alpha" value="1"
+ summary="the requested alpha value is outside the interval [0, 1]"/>
+ </enum>
+
+ <request name="destroy" type="destructor">
+ <description summary="remove blending from the surface">
+ The associated wl_surface's blending state is removed.
+ The change is applied on the next wl_surface.commit.
+ </description>
+ </request>
+
+ <request name="set_blending">
+ <description summary="set the blending equation">
+ Set the blending equation for compositing the wl_surface.
+
+ If the requested format was not advertised by the
+ zwp_alpha_compositing_v1.blending event, the INVALID_EQUATION protocol
+ error is raised.
+
+ The blending equation state is double-buffered state,
+ and will be applied on the next wl_surface.commit.
+ </description>
+ <arg name="equation" type="uint" summary="the new blending equation"/>
+ </request>
+
+ <request name="set_alpha">
+ <description summary="set the alpha value">
+ Set the alpha value applied to the whole surface for compositing. This
+ alpha value is applied as an additional step after the processing of
+ per-pixel alpha values for the wl_surface.
+
+ If the requested alpha is outside the interval [0, 1], the
+ INVALID_ALPHA protocol error is raised.
+
+ The alpha value state is double-buffered state,
+ and will be applied on the next wl_surface.commit.
+ </description>
+ <arg name="value" type="fixed" summary="the new alpha value"/>
+ </request>
+ </interface>
+
+</protocol>

[Simon Ser]

Hi Alexandros and Scott,

Here are a few small comments. Overall this proposal looks good.

Post by Scott Anderson
This protocol specifies a set of interfaces used to control the alpha
compositing and blending of surface contents.
It's based on the Chromium Wayland protocol of the same name ([1]) and
an old proposal of this protocol ([2]).
- Add additional "fromsource" blending equation used by [3]
- Allow the server to advertise which blending equations it supports
- Added a protocol errors for using an unsupported equation
- Added a protocol error for using an invalid alpha value
- Added clarification about wl_surface.set_opaque_region
- Added clarification about per-pixel alpha values

This should probably not be part of the commit message (ie. be after "---").

Post by Scott Anderson
https://gitlab.freedesktop.org/ascent/weston/tree/alpha-compositing-v1

[1] https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/alpha-compositing/alpha-compositing-u> nstable-v1.xml

Post by Scott Anderson
[2] https://lists.freedesktop.org/archives/wayland-devel/2017-August/034741.html
[3] https://lists.freedesktop.org/archives/wayland-devel/2018-September/039437.html

Signed-off-by tags are missing here.

Post by Scott Anderson
---
Makefile.am | 1 +
unstable/alpha-compositing/README | 5 +
.../alpha-compositing-unstable-v1.xml | 172 ++++++++++++++++++
3 files changed, 178 insertions(+)
create mode 100644 unstable/alpha-compositing/README
create mode 100644 unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
diff --git a/Makefile.am b/Makefile.am
index 6394e26..ac6c9f8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -21,6 +21,7 @@ unstable_protocols = \
unstable/xdg-output/xdg-output-unstable-v1.xml \
unstable/input-timestamps/input-timestamps-unstable-v1.xml \
unstable/xdg-decoration/xdg-decoration-unstable-v1.xml \
+ unstable/alpha-compositing/alpha-compositing-unstable-v1.xml \
$(NULL)
stable_protocols = \
diff --git a/unstable/alpha-compositing/README b/unstable/alpha-compositing/README
new file mode 100644
index 0000000..5826967
--- /dev/null
+++ b/unstable/alpha-compositing/README
@@ -0,0 +1,5 @@
+Alpha compositing protocol
+
diff --git a/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml b/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
new file mode 100644
index 0000000..aae1d6e
--- /dev/null
+++ b/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
@@ -0,0 +1,172 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="alpha_compositing_unstable_v1">
+
+ <copyright>
+ Copyright 2016 The Chromium Authors.
+ Copyright 2017-2018 Collabora Ltd
+ Copyright 2018 NXP
+
+ Permission is hereby granted, free of charge, to any person obtaining a
+ copy of this software and associated documentation files (the "Software"),
+ to deal in the Software without restriction, including without limitation
+ the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ and/or sell copies of the Software, and to permit persons to whom the
+
+ The above copyright notice and this permission notice (including the next
+ paragraph) shall be included in all copies or substantial portions of the
+ Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ DEALINGS IN THE SOFTWARE.
+ </copyright>
+
+ <description summary="Protocol for more advanced compositing and blending">
+ This protocol specifies a set of interfaces used to control the alpha
+ compositing and blending of surface contents.
+
+ Warning! The protocol described in this file is experimental and backward
+ incompatible changes may be made. Backward compatible changes may be added
+ together with the corresponding interface version bump. Backward
+ incompatible changes are done by bumping the version number in the protocol
+ and interface names and resetting the interface version. Once the protocol
+ is to be declared stable, the 'z' prefix and the version number in the
+ protocol and interface names are removed and the interface version number is
+ reset.
+ </description>
+
+ <interface name="zwp_alpha_compositing_v1" version="1">
+ <description summary="alpha_compositing">

Maybe the "_" can be removed here? This value is supposed to be human-readable.

Post by Scott Anderson
+ The global interface exposing compositing and blending capabilities is
+ used to instantiate an interface extension for a wl_surface object.
+ This extended interface will then allow the client to specify the
+ blending equation and alpha value used for compositing the wl_surface.
+ </description>
+
+ <enum name="error">
+ <entry name="blending_exists" value="0"
+ summary="the surface already has a blending object associated"/>
+ </enum>
+
+ <request name="destroy" type="destructor">
+ <description summary="unbind from the blending interface">
+ Informs the server that the client will not be using this
+ protocol object anymore. This does not affect any other objects,
+ blending objects included.
+ </description>
+ </request>
+
+ <request name="get_blending">
+ <description summary="extend surface interface for blending">
+ Instantiate an interface extension for the given wl_surface to
+ provide surface blending. If the given wl_surface already has
+ a blending object associated, the BLENDING_EXISTS protocol error
+ is raised.
+ </description>
+
+ <arg name="id" type="new_id" interface="zwp_blending_v1"
+ summary="the new blending interface id"/>
+ <arg name="surface" type="object" interface="wl_surface"
+ summary="the surface"/>
+ </request>
+
+ <event name="blending">

Maybe this could be called "blending_equation"? Using only "blending" is
confusing because there's already a "get_blending" request that creates
"zwp_blending_v1" objects.

Post by Scott Anderson
+ <description summary="supported blending equations">
+ This event advertistes the blending equations that the server

advertises

Post by Scott Anderson
+ supports. All the supported blending equations are advertised once
+ when the client binds to this interface. A roundtrip after binding
+ gurantees that the client has received all supported blending

guarantees

Post by Scott Anderson
+ equations.
+
+ For the definition of the blending equations, see the
+ zwp_blending_v1.blending_equation enum.
+
+ The server must always advertise the 'none' blending equation.
+ </description>
+ <arg name="equation" type="uint" summary="the blending equation"/>

enum="zwp_blending_v1.blending_equation"

Post by Scott Anderson
+ </event>
+ </interface>
+
+ <interface name="zwp_blending_v1" version="1">
+ <description summary="blending interface to a wl_surface">
+ An additional interface to a wl_surface object, which allows the
+ client to specify the blending equation used for compositing and
+ an alpha value applied to the whole surface.
+
+ When the blending object is created its blending equation is
+ 'none' and its alpha is 1.0, i.e., it's inactive by default. Clients
+ can activate it by setting the blending equation and alpha value.
+
+ Use of this interface has no effect on the surface's opaque region
+ as set by wl_surface.set_opaque_region. Clients must make sure to set
+ their opaque region correctly to prevent repaint artifacts.
+
+ If the wl_surface associated with the blending object is destroyed,
+ the blending object becomes inert.
+
+ If the blending object is destroyed, the blending state is removed
+ from the wl_surface. The change will be applied on the next
+ wl_surface.commit.
+ </description>
+
+ <enum name="blending_equation">
+ <description summary="different blending equations for compositing">
+ Blending equations that can be used when compositing a surface.
+ </description>
+ <entry name="none" value="0" summary="blending object is inactive"/>
+ <entry name="opaque" value="1" summary="(one, zero)"/>
+ <entry name="premultiplied" value="2" summary="(one, one_minus_src_alpha)"/>
+ <entry name="straight" value="3" summary="(src_alpha, one_minus_src_alpha)"/>
+ <entry name="fromsource" value="4" summary="(src_alpha, src_alpha)"/>
+ </enum>
+
+ <enum name="error">
+ <entry name="invalid_equation" value="0"
+ summary="the blending equation is not supported"/>
+ <entry name="invalid_alpha" value="1"
+ summary="the requested alpha value is outside the interval [0, 1]"/>
+ </enum>
+
+ <request name="destroy" type="destructor">
+ <description summary="remove blending from the surface">
+ The associated wl_surface's blending state is removed.
+ The change is applied on the next wl_surface.commit.
+ </description>
+ </request>
+
+ <request name="set_blending">
+ <description summary="set the blending equation">
+ Set the blending equation for compositing the wl_surface.
+
+ If the requested format was not advertised by the
+ zwp_alpha_compositing_v1.blending event, the INVALID_EQUATION protocol
+ error is raised.
+
+ The blending equation state is double-buffered state,
+ and will be applied on the next wl_surface.commit.
+ </description>
+ <arg name="equation" type="uint" summary="the new blending equation"/>
+ </request>
+
+ <request name="set_alpha">
+ <description summary="set the alpha value">
+ Set the alpha value applied to the whole surface for compositing. This
+ alpha value is applied as an additional step after the processing of
+ per-pixel alpha values for the wl_surface.
+
+ If the requested alpha is outside the interval [0, 1], the
+ INVALID_ALPHA protocol error is raised.
+
+ The alpha value state is double-buffered state,
+ and will be applied on the next wl_surface.commit.
+ </description>
+ <arg name="value" type="fixed" summary="the new alpha value"/>
+ </request>
+ </interface>
+
+</protocol>
--
2.19.1
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