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

Scott Anderson scott.anderson at collabora.com
Wed Nov 14 04:04:35 UTC 2018


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 <reveman at chromium.org>
+Alexandros Frantzis <alexandros.frantzis at 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>
-- 
2.19.1



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