[RFC krh/wayland/next 2/2] protocol: try to clarify wl_buffer doc

[Pekka Paalanen]

On Fri, 12 Oct 2012 14:29:01 +0300
Pekka Paalanen <ppaalanen at gmail.com> wrote:

> 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 at gmail.com>
> Signed-off-by: Pekka Paalanen <ppaalanen at gmail.com>
> ---
>  protocol/wayland.xml |   28 +++++++++++++---------------
>  1 files changed, 13 insertions(+), 15 deletions(-)
> 
> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> index bd05c75..1b75f9b 100644
> --- 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.

Are these two not really an improvement?


Thanks,
pq