[PATCH v2] protocol: Improve data source notification around DnD progress

[Jonas Ådahl]

On Fri, Oct 30, 2015 at 09:55:37PM +0100, Carlos Garnacho wrote:
> Currently, there's no means for the DnD origin to know whether the
> destination is actually finished with the DnD transaction, short of
> finalizing it after the first transfer finishes, or leaking it forever.
> 
> But this poses other interoperation problems, drag destinations might
> be requesting several mimetypes at once, might be just poking to find
> out the most suitable format, might want to defer the action to a popup,
> might be poking contents early before the selection was dropped...
> 
> In addition, data_source.cancelled is suitable for the situations where
> the DnD operation fails (not on a drop target, no matching mimetypes,
> etc..), but seems undocumented for that use (and unused in weston's DnD).
> 
> In order to improve the situation, the drag source should be notified
> of all stages of DnD. In addition to documenting the "cancelled" event
> for DnD purposes, The following 2 events have been added:
> 
> - wl_data_source.dnd_performed: Happens when the operation has been
>   physically finished (eg. the button is released), it could be the right
>   place to reset the pointer cursor back and undo any other state resulting
>   from the initial button press.
> - wl_data_source.dnd_finished: Happens when the destination side destroys
>   the wl_data_offer, at this point the source can just forget all data
>   related to the DnD selection as well, plus optionally deleting the data
>   on move operations.
> 
> Changes since v1:
>   - Renamed events to have a common "dnd" namespace. Made dnd_performed to
>     happen invariably, data_device.cancelled may still happen afterwards.
> 
> Signed-off-by: Carlos Garnacho <carlosg at gnome.org>
> ---
>  protocol/wayland.xml | 47 +++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 41 insertions(+), 6 deletions(-)
> 
> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> index 59819e9..477ef55 100644
> --- a/protocol/wayland.xml
> +++ b/protocol/wayland.xml
> @@ -408,7 +408,7 @@
>    </interface>
>  
>  
> -  <interface name="wl_data_offer" version="1">
> +  <interface name="wl_data_offer" version="3">
>      <description summary="offer to transfer data">
>        A wl_data_offer represents a piece of data offered for transfer
>        by another client (the source client).  It is used by the
> @@ -423,7 +423,9 @@
>  	Indicate that the client can accept the given mime type, or
>  	NULL for not accepted.
>  
> -	Used for feedback during drag-and-drop.
> +	This request mandates the final result of the drag-and-drop
> +	operation. If the end result is that no mimetype is accepted,
> +	the drag source will receive drag_source.cancelled.

This adds requirements to how to use .accept, but doesn't specify
whether they are only added for version >= 3 or not, making this part
change the previous versions of the protocol.

If we want to change the previous versions, we need to be sure the new
behavior was the actual intended behavior (as for when we changed
wl_subsurface's commit behaviour), and make that change as a separate
commit with its own explanation.

Otherwise we need to make it clear that the new requirements of the
"accept" request is only relevant for version >= 3.

Other than this, either with the "dnd_performed" renamed to
"dnd_drop_performed" or not, this one is
Reviewed-by: Jonas Ådahl <jadahl at gmail.com>


Jonas

>        </description>
>  
>        <arg name="serial" type="uint"/>
> @@ -463,7 +465,7 @@
>      </event>
>    </interface>
>  
> -  <interface name="wl_data_source" version="1">
> +  <interface name="wl_data_source" version="3">
>      <description summary="offer to transfer data">
>        The wl_data_source object is the source side of a wl_data_offer.
>        It is created by the source client in a data transfer and
> @@ -510,14 +512,47 @@
>  
>      <event name="cancelled">
>        <description summary="selection was cancelled">
> -	This data source has been replaced by another data source.
> +	This data source is no longer valid. There are several reasons why
> +	this could happen:
> +
> +	- The data source has been replaced by another data source.
> +	- The drag-and-drop operation was performed, but the drop destination
> +          did not accept any of the mimetypes offered through
> +          data_source.target.
> +	- The drag-and-drop operation was performed but didn't happen over a
> +          surface.
> +	- The compositor cancelled the drag-and-drop operation
> +
>  	The client should clean up and destroy this data source.
>        </description>
>      </event>
>  
> +    <!-- Version 3 additions -->
> +
> +    <event name="dnd_performed" since="3">
> +      <description summary="the drag-and-drop operation physically finished">
> +	The user performed the drop action. This event does not indicate
> +	acceptance, data_source.cancelled may still be emitted afterwards
> +	if the drop destination does not accept any mimetype.
> +
> +	This event might however not be received if the compositor cancelled
> +	the drag-and-drop operation before this event could happen.
> +
> +	Note that the data_source may still be used further in the future and
> +	should not be destroyed here.
> +      </description>
> +    </event>
> +
> +    <event name="dnd_finished" since="3">
> +      <description summary="the drag-and-drop operation concluded">
> +	The drop destination finished interoperating with this data
> +	source, the client is now free to destroy this data source and
> +	free all associated data.
> +      </description>
> +    </event>
>    </interface>
>  
> -  <interface name="wl_data_device" version="2">
> +  <interface name="wl_data_device" version="3">
>      <description summary="data transfer device">
>        There is one wl_data_device per seat which can be obtained
>        from the global wl_data_device_manager singleton.
> @@ -659,7 +694,7 @@
>      </request>
>    </interface>
>  
> -  <interface name="wl_data_device_manager" version="2">
> +  <interface name="wl_data_device_manager" version="3">
>      <description summary="data transfer interface">
>        The wl_data_device_manager is a singleton global object that
>        provides access to inter-client data transfer mechanisms such as
> -- 
> 2.5.0
> 
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