color-management: add wp_image_description_reference_v1

Note that wp_image_description_v1 is not a frozen interface. Therefore
it must always be a descendant of wp_color_manager_v1.

In order to allow other protocols, such as ext-image-capture-source-v1,
to define the equivalent of
wp_color_management_output_v1.get_image_description, we must therefore
create an indirection between the new protocol and
wp_image_description_v1 that is resolved through wp_color_manager_v1
itself.

This is a prerequisite for adding color management support to the
ext-image-copy-capture-v1 protocol.

Signed-off-by: Julian Orth <ju.orth@gmail.com>

Author: mahkoh

staging/color-management/color-management-v1.xml

@@ -581,6 +581,20 @@
         transfer functions and named primaries have been sent.
       </description>
     </event>
+
+    <request name="get_image_description" since="2">
+      <description summary="create an image description from a reference">
+        This request retrieves the image description backing a reference.
+
+        The get_information request can be used if and only if the request that
+        creates the reference allows it.
+      </description>
+
+      <arg name="image_description"
+           type="new_id" interface="wp_image_description_v1"/>
+      <arg name="reference"
+           type="object" interface="wp_image_description_reference_v1"/>
+    </request>
   </interface>
 
   <interface name="wp_color_management_output_v1" version="2">
@@ -1689,4 +1703,22 @@
            summary="Maximum frame-average light level (cd/m²)"/>
     </event>
   </interface>
+
+  <interface name="wp_image_description_reference_v1" version="1">
+    <description summary="Reference to an image description">
+      This object is a reference to an image description. This interface is
+      frozen at version 1 to allow other protocols to create
+      wp_image_description_v1 objects.
+
+      The wp_color_manager_v1.get_image_description request can be used to
+      retrieve the underlying image description.
+    </description>
+
+    <request name="destroy" type="destructor">
+      <description summary="destroy the reference">
+        Destroy this object. This has no effect on the referenced image
+        description.
+      </description>
+    </request>
+  </interface>
 </protocol>