staging: add tearing control protocol

For some use cases like games or drawing tablets it can make sense to reduce
latency by accepting tearing with the use of asynchronous page flips. This
protocol provides a way for clients to indicate whether or not their content
is suitable for this kind of presentation.

Signed-off-by: Xaver Hugl <xaver.hugl@gmail.com>

3 files changed, 125 insertions, 0 deletions

diff --git a/meson.build b/meson.build
index 3f2f008..1b347ae 100644
--- a/meson.build
+++ b/meson.build
@@ -41,6 +41,7 @@ staging_protocols = {
 	'ext-idle-notify': ['v1'],
 	'ext-session-lock': ['v1'],
 	'single-pixel-buffer': ['v1'],
+	'tearing-control': ['v1'],
 	'xdg-activation': ['v1'],
 	'xwayland-shell': ['v1'],
 }
diff --git a/staging/tearing-control/README b/staging/tearing-control/README
new file mode 100644
index 0000000..cdd3ca9
--- /dev/null
+++ b/staging/tearing-control/README
@@ -0,0 +1,4 @@
+Tearing control protocol
+
+Maintainers:
+Xaver Hugl <xaver.hugl@gmail.com>
diff --git a/staging/tearing-control/tearing-control-v1.xml b/staging/tearing-control/tearing-control-v1.xml
new file mode 100644
index 0000000..e38056d
--- /dev/null
+++ b/staging/tearing-control/tearing-control-v1.xml
@@ -0,0 +1,120 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<protocol name="tearing_control_v1">
+  <copyright>
+    Copyright © 2021 Xaver Hugl
+
+    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>
+
+  <interface name="wp_tearing_control_manager_v1" version="1">
+    <description summary="protocol for tearing control">
+      For some use cases like games or drawing tablets it can make sense to
+      reduce latency by accepting tearing with the use of asynchronous page
+      flips. This global is a factory interface, allowing clients to inform
+      which type of presentation the content of their surfaces is suitable for.
+
+      Graphics APIs like EGL or Vulkan, that manage the buffer queue and commits
+      of a wl_surface themselves, are likely to be using this extension
+      internally. If a client is using such an API for a wl_surface, it should
+      not directly use this extension on that surface, to avoid raising a
+      tearing_control_exists protocol error.
+
+      Warning! The protocol described in this file is currently in the testing
+      phase. Backward compatible changes may be added together with the
+      corresponding interface version bump. Backward incompatible changes can
+      only be done by creating a new major version of the extension.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy tearing control factory object">
+        Destroy this tearing control factory object. Other objects, including
+        wp_tearing_control_v1 objects created by this factory, are not affected
+        by this request.
+      </description>
+    </request>
+
+    <enum name="error">
+      <entry name="tearing_control_exists" value="0"
+             summary="the surface already has a tearing object associated"/>
+    </enum>
+
+    <request name="get_tearing_control">
+      <description summary="extend surface interface for tearing control">
+        Instantiate an interface extension for the given wl_surface to request
+        asynchronous page flips for presentation.
+
+        If the given wl_surface already has a wp_tearing_control_v1 object
+        associated, the tearing_control_exists protocol error is raised.
+      </description>
+      <arg name="id" type="new_id" interface="wp_tearing_control_v1"/>
+      <arg name="surface" type="object" interface="wl_surface"/>
+    </request>
+  </interface>
+
+  <interface name="wp_tearing_control_v1" version="1">
+    <description summary="per-surface tearing control interface">
+      An additional interface to a wl_surface object, which allows the client
+      to hint to the compositor if the content on the surface is suitable for
+      presentation with tearing.
+      The default presentation hint is vsync. See presentation_hint for more
+      details.
+    </description>
+
+    <enum name="presentation_hint">
+      <description summary="presentation hint values">
+        This enum provides information for if submitted frames from the client
+        may be presented with tearing.
+      </description>
+      <entry name="vsync" value="0">
+        <description summary="tearing-free presentation">
+          The content of this surface is meant to be synchronized to the
+          vertical blanking period. This should not result in visible tearing
+          and may result in a delay before a surface commit is presented.
+        </description>
+      </entry>
+      <entry name="async" value="1">
+        <description summary="asynchronous presentation">
+          The content of this surface is meant to be presented with minimal
+          latency and tearing is acceptable.
+        </description>
+      </entry>
+    </enum>
+
+    <request name="set_presentation_hint">
+      <description summary="set presentation hint">
+        Set the presentation hint for the associated wl_surface. This state is
+        double-buffered and is applied on the next wl_surface.commit.
+
+        The compositor is free to dynamically respect or ignore this hint based
+        on various conditions like hardware capabilities, surface state and
+        user preferences.
+      </description>
+      <arg name="hint" type="uint" enum="presentation_hint"/>
+    </request>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy tearing control object">
+        Destroy this surface tearing object and revert the presentation hint to
+        vsync. The change will be applied on the next wl_surface.commit.
+      </description>
+    </request>
+  </interface>
+
+</protocol>