protocol: try to clarify wl_buffer doc

Fix few typos in wl_buffer description.

Mention backing storage in wl_buffer.destroy.

Try to clarify the wl_buffer.release semantics by not explaining what
*might* happen. It is important to not suggest, that if release does not
come before frame callback, it will not come before attaching a new
buffer to the surface. We want to allow the following scenario:

The compositor is able to texture from wl_buffers directly, but it also
keeps a copy of the surface contents. The copy is updated when the
compositor is idle, to avoid the performance hit on
wl_surface.attach/commit. When the copy completes some time later, the
server sends the release event. If the client has not yet allocated a
second buffer (e.g. it updates rarely), it can reuse the old buffer.

Reported-by: John Kåre Alsaker <john.kare.alsaker@gmail.com>
Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index e88cc95..019816d 100644 (file)
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -226,16 +226,17 @@
 
   <interface name="wl_buffer" version="1">
     <description summary="content for a wl_surface">
-      A buffer provides the content for a wl_surface.  Buffers are
+      A buffer provides the content for a wl_surface. Buffers are
       created through factory interfaces such as wl_drm, wl_shm or
-      similar.  It has a width and a height and can be attached to a
+      similar. It has a width and a height and can be attached to a
       wl_surface, but the mechanism by which a client provides and
-      updates the contents is defined by the buffer factory interface
+      updates the contents is defined by the buffer factory interface.
     </description>
 
     <request name="destroy" type="destructor">
       <description summary="destroy a buffer">
-       Destroy a buffer.  This will invalidate the object id.
+       Destroy a buffer. If and how you need to release the backing
+       storage is defined by the buffer factory interface.
 
        For possible side-effects to a surface, see wl_surface.attach.
       </description>
@@ -244,17 +245,14 @@
     <event name="release">
       <description summary="compositor releases buffer">
        Sent when this wl_buffer is no longer used by the compositor.
-
-       If a client does not get a release event before the frame callback
-       requested in the same wl_surface.commit that attaches this wl_buffer
-       to a surface, then the client may assume, that the compositor will
-       be using this wl_buffer until the client attaches another wl_buffer.
-       Therefore the client will need a second wl_buffer to update the
-       surface contents again.
-
-       Otherwise, if a release event arrives before the frame callback, the
-       client is immediately free to re-use the buffer and its backing
-       storage, and does not necessarily need a second buffer. Typically
+       The client is now free to re-use or destroy this buffer and its
+       backing storage.
+
+       If a client receives a release event before the frame callback
+       requested in the same wl_surface.commit that attaches this
+       wl_buffer to a surface, then the client is immediately free to
+       re-use the buffer and its backing storage, and does not need a
+       second buffer for the next surface content update. Typically
        this is possible, when the compositor maintains a copy of the
        wl_surface contents, e.g. as a GL texture. This is an important
        optimization for GL(ES) compositors with wl_shm clients.