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

[Bill Spitzak]

On Thu, Oct 29, 2015 at 9:51 PM, Jonas Ådahl <jadahl at gmail.com> wrote:

>
> > > I too would like some clarifications why this is needed. The cursor and
> > > button state, I assume, could be reset on the next enter or by
> > > cancelled/finished, but that the client may want update its UI in some
> > > way.
>


> As long as there needs to be no UI/behavioural changes as a result of
> ending this grab, ending it at the next 'enter' I guess would be just
> fine, but as long as UI needs to react to the drop immediately, it seems
> necessary.
>

I think everybody was confused by the mention of "restoring the cursor".
That is *not* something the DnD source would do and it threw everybody off
trying to comment on this.

I think what is wanted is an indication that the drag really did finish.
For instance a file browser acting as the source of a "move" action will
want a confirmation that the move actually worked before it actually
destroys the source file. This confirmation can happen long after the dnd
action is negotiated and after all the data is transferred. Imagine if the
destination suddenly encounters an error trying to write the file to the
destination disk. It does seem like toolkits are purposely delaying
messages that were designed to be sent asap in other DnD protocols in order
to achieve this.

I guess some kind of event sent to the source would work for this. There
should probably be success and failure forms of the event, and maybe even a
progress indicator (then you could do movie-style gui where the files
gradually vanish as they are deleted).
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