Discussion:
[RFC wayland-protocols] Add alpha-compositing protocol
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Alexandros Frantzis
2017-08-08 14:24:58 UTC
Permalink
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]),
with a few changes made to the blending_equation enumeration.

A proof-of-concept implementation for Weston can be found at:

https://git.collabora.com/cgit/user/alf/weston.git/log/?h=alpha-compositing-v1

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

---
Makefile.am | 1 +
unstable/alpha-compositing/README | 5 +
.../alpha-compositing-unstable-v1.xml | 134 +++++++++++++++++++++
3 files changed, 140 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 5b5ae96..eca1f4e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -15,6 +15,7 @@ unstable_protocols = \
unstable/xwayland-keyboard-grab/xwayland-keyboard-grab-unstable-v1.xml \
unstable/keyboard-shortcuts-inhibit/keyboard-shortcuts-inhibit-unstable-v1.xml \
unstable/xdg-output/xdg-output-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..8101db1
--- /dev/null
+++ b/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
@@ -0,0 +1,134 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="alpha_compositing_unstable_v1">
+
+ <copyright>
+ Copyright 2016 The Chromium Authors.
+ Copyright 2017 Collabora Ltd
+
+ 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>
+
+ <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>
+
+ <enum name="error">
+ <entry name="blending_exists" value="0"
+ summary="the surface already has a blending object associated"/>
+ </enum>
+
+ <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>
+ </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.
+
+ 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>
+
+ <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>
+
+ <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)" />
+ </enum>
+
+ <request name="set_blending">
+ <description summary="set the blending equation">
+ Set the blending equation for compositing the wl_surface.
+
+ 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.
+
+ 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>
--
2.13.2
Gary Bisson
2018-09-07 14:02:24 UTC
Permalink
Hi Alexandros, All,
Post by Alexandros Frantzis
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]),
with a few changes made to the blending_equation enumeration.
https://git.collabora.com/cgit/user/alf/weston.git/log/?h=alpha-compositing-v1
[1] https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
Was there any feedback on this RFC? On top of Chromium, it seems that
NXP is now also using it for its i.MX processors [2]. So it would
definitely be great to have this protocol upstream.

Note that NXP apparently modified this version of the patch a bit.

Regards,
Gary

[2] https://source.codeaurora.org/external/imx/wayland-protocols-imx/commit/?id=799164a4
Alexandros Frantzis
2018-09-10 09:14:57 UTC
Permalink
Post by Gary Bisson
Hi Alexandros, All,
Post by Alexandros Frantzis
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]),
with a few changes made to the blending_equation enumeration.
https://git.collabora.com/cgit/user/alf/weston.git/log/?h=alpha-compositing-v1
[1] https://chromium.googlesource.com/chromium/src/+/master/third_party/wayland-protocols/unstable/alpha-compositing/alpha-compositing-unstable-v1.xml
Was there any feedback on this RFC? On top of Chromium, it seems that
NXP is now also using it for its i.MX processors [2]. So it would
definitely be great to have this protocol upstream.
Note that NXP apparently modified this version of the patch a bit.
Regards,
Gary
[2] https://source.codeaurora.org/external/imx/wayland-protocols-imx/commit/?id=799164a4
Hi Gary,

thanks for bringing the i.MX version to my/our attention.

I haven't received any feedback about this proposal so far, but I am
happy to revive the upstreaming effort as soon as I do. To this end, I
have also added Haihua Hu (from NXP) to the CC list for this thread.

Thanks,
Alexandros
Daniel Stone
2018-11-06 11:15:11 UTC
Permalink
Hi Alexandros,

On Tue, 8 Aug 2017 at 15:25, Alexandros Frantzis
Post by Alexandros Frantzis
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]),
with a few changes made to the blending_equation enumeration.
[...]
+ <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.
This doesn't specify any interaction with per-pixel alpha values. Is
it an additional step after per-pixel alpha, or does it replace
per-pixel alpha?

Beyond that, looks good to me.

Cheers,
Daniel

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