[PATCH weston 1/3] Introduce pointer lock interface

Jason Ekstrand jason at jlekstrand.net
Tue Sep 23 14:42:35 PDT 2014

Hi Matthieu,
Could you please provide more explanation on what use-cases you are
considering and why the current proposal fails to accomplish them?  All I
was able to get from your post was the example of a TV remote.  It's all
well and good to completely disagree with the proposed approach, but
without a good reason as to why it doesn't work, it's kind of moot.

It's also worth noting the scope of the proposal.  The primary objective
here is to provide a mechanism to take a device that could be providing
relative events but which the compositor has turned into a pointer and get
the relative events out of it.  It's not intended to be a generic system
for getting relative events.

On that note, if you want to get a generic relative motion events, can't
you just open the device and read them?  Sure we could cobble together a
specification for how to read a bunch of buttons and relative events and
then create a cursor from them.  I'm pretty sure it exists in the form of
the USB HID spec.  How does reimplementing that in Wayland help us?  There
was, at one point, a proposal for gamepads, but nothing has happened there
in a while.

On Tue, Sep 23, 2014 at 9:01 AM, Matthieu Gautier <dev at mgautier.fr> wrote:

> Hello,
> I'm pretty new into wayland and the discussion is relatively long, so I
> may have missed arguments/constraints.
> However I would like to share my point of view.
> It seems to me that we are taking the problem the wrong way.
> Relative motions exist as soon as there is a device generating them.
> wl_pointer is just a particular interpretation of those events.
> In fact, we may have a system where we have relative motion events but no
> wl_pointer. Think about a smart tv with a remote control with
> accelerator/gyroscope detectors.
> This remote may behave as a mouse, generating relative motion events. But
> the main interface of the TV may have no pointer. The interface should been
> a set of icons and user move between them with the remote buttons.

If you're just pressing buttons to move between icons, then "pointer" is
probably the wrong way to look at it anyway.  It's more "arrow keys" than a

> In the same way, we may want that special applications still have access
> to motion events:
> - A web browser that will display itself the pointer (or activate
> wl_pointer in the compositor)
> - A video game
> - Any application that want make gesture recognition.
> In this context, wl_pointer is a special use-case of a shell and having a
> mouse device doesn't imply having a pointer.
> Relative motions should be always available (if there is a device) and
> wl_pointer should be created on top of relative motions.
> Trying to reduce the wl_pointer behavior to have the raw events seems to
> me the contrary of what we have to do.
> What I propose is :
> - Having a way to get "relative input object" (lets call it wl_relative
> for now) from wl_seat.
> - Having a way to get a wl_pointer from the wl_seat at it is already the
> case.
> Relative events a sent to client if it is active (It is to the compositor
> to decide this, as usual) whatever there is a wl_pointer or not.
> The pointer lock interface will become some kind of "deactivate/configure
> wl_pointer".
> # Functionally :
> A combination of :
> - Hide the cursor (already available with wl_pointer.set_cursor)
> - Don't not update wl_pointer position from relative events.
> - Confine the pointer position into my wl_surface.
> - Set wl_pointer at this position.
> - A fps game will hide the cursor and deactivate update of wl_pointer
> position.
> - A strategy game will just confine the pointer.
> - A application with a 3D view that what to rotate it when user drag the
> mouse will just deactivate update of pointer position between button_down
> and button_up.
> - A application that just want relative motion events do nothing.
> At any time, relative motion events are sent to client through the
> wl_relative object. Regardless of the state of wl_pointer.
> It is up to the client to handle events from wl_pointer or wl_relative
> depending of which kind of information it wants.
> # Interface :
> The wl_pointer could gain two (four?) more requests :
> - set_mode(mode, callback)
> - reset_mode()
> ( - has_mode
> - get_mode )
> The default mode is the mode we have for now (no special constraints)
> A client can change the mode of a wl_pointer. It gets a callback.
> When compositor stops the special mode (or refuse it) the done event of
> the callback is sent.
> When the client has finished with special mode, it sends the reset_mode
> request.
> The wl_pointer.leave event may or not be sent to client when the done
> event is sent (The pointer may still being inside the wl_surface when
> special mode ends)
> However a wl_pointer.leave event implies a done event. (We cannot have a
> special mode if we don't have the pointer focus)
> On the interface to get the wl_relative object from seat, it depends :
> Is there a possibility to have several cursor on one seat ?

One cursor per seat.  If there are multiple physical mice, then you get an
aggregate of all the mice.  You can, however, have multiple seats in which
case you will get multiple pointers.

> (Two mouses moving two cursors)
> Does wl_seat.get_cursor return always a proxy to the same object ?

Yes, all pointers created from the same seat are identical.

> - If there is only one cursor, we can simply add a get_relative request to
> wl_seat.
> - If not, we should get a object from the other.
>   . Ideally, get the wl_pointer from wl_relative. (and wl_relative from
> wl_seat)
>   . Practically, cause of the existent, get wl_relative from wl_pointer.
> Regards,
> Matthieu Gautier.
> _______________________________________________
> wayland-devel mailing list
> wayland-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
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