[PATCH wayland v4] protocol: Add DnD actions

[Daniel Stone]

Hi,

On Wednesday, 30 September 2015, Carlos Garnacho <carlosg at gnome.org> wrote:

> These 2 requests have been added:
>
> - wl_data_source.set_actions: Notifies the compositor of the available
>   actions on the data source.
> - wl_data_offer.set_actions: Notifies the compositor of the available
>   actions on the destination side, plus the preferred action.
>
> Out of the data from these requests, the compositor can determine the
> action
> both parts agree on (and let the user play a role through eg. keyboard
> modifiers). The chosen option will be notified to both parties
> through the following two requests:
>
> - wl_data_source.action
> - wl_data_offer.action
>
> In addition, the destination side can peek the source side actions through
> wl_data_offer.source_actions.
>
> Compared to the XDND protocol, there's two notable changes:
>
> - XDND lets the source suggest an action, whereas wl_data_device lets
>   the destination prefer a given action. The difference is subtle here,
>   it comes off as convenience because it is the drag destination which
>   receives the motion events (unlike in X) and can perform action updates.
>
>   The drag destination seems also in a better position to update the
>   preferred action based on things like the data being transferred, the
>   place being dropped, and whether the drag is client-local.
>
> - That same source-side preferred action is used in XDND to convey the
>   modifier-induced action to the drag destination, which would then ack
>   it, or reply with another action that's accepted (or none), this makes
>   the XdndPosition/XdndStatus messaging very verbose, and synchronous
>   because the drag source always needs to know the latest status/action
>   for every position+action sent.
>
>   Here it's the compositor which takes care of modifiers and matching
>   available/accepted actions, this allows for the signaling to happen
>   only whenever the actions/modifiers change for real.
>
> Roughly based on previous work by Giulio Camuffo <giuliocamuffo at gmail.com
> <javascript:;>>
>

Mike had a look at this from EFL - CCing him.

Cheers,
Daniel
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