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

[Bill Spitzak]

On Thu, Oct 29, 2015 at 9:51 AM, Carlos Garnacho <carlosg at gnome.org> wrote:

> So this x11-style "grab" still happens before start_drag on the
> compositor, all it currently does face to the wayland compositor is
> updating the pointer cursor, but client-side it brings the usual
> grabby effects, input still taken "elsewhere", etc. However, we don't
> have a place to finish this grab, waiting for the next enter event
> strikes me as too late, plus this enter event might be
> undistinguishable from a not-after-dnd one at the windowing layer. It
> is similar for drag_finished, an "ask" action (as per the other patch)
> could trigger a popup, which would mess with this grab state if
> source==dest.
>

We are not talking about an enter event received by the DnD source client.
We are talking about an enter event that is sent to whatever client happens
to be under the mouse cursor after the button is released. This is probably
the DnD target client but could be anybody. These clients are already
required to reset the mouse cursor on enter events so the mouse cursor will
be fixed then, with NO work done by the source.

The problem is that you seem to be comparing this to an X11 "active grab",
possibly because of the kludges done to implement XDND. Think of it as a
*passive* grab, exactly the same thing that you get when the user pushes
the mouse button down and drags the cursor outside the client. The source
client gets the mouse-up event, and there does not seem to be any need for
another event to indicate that the drag is done, and resetting the mouse
cursor is the job of whatever client is now under the cursor.
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