[RFC PATCH v3 wayland] protocol: add wl_pointer.axis_source, axis_stop and axis_discrete events

Tue Jun 2 01:06:23 PDT 2015

Hi,

I think this looks pretty decent now. Currently I have no more issues
with the protocol, only minor nits and comments on wording etc. that can
be found inline. Assuming those are addressed, this patch has my
Reviewed-by.

On Thu, May 07, 2015 at 03:54:08PM +1000, Peter Hutterer wrote:
> The axis_source event determines how an axis event was generated. That enables
> clients to judge when to use kinetic scrolling.
> 
> The axis_stop event notifies a client about the termination of a scroll
> sequence, likewise needed to calculate kinetic scrolling parameters.
> 
> The axis_discrete event provides the wheel click count. Previously the axis
> value was some hardcoded number (10), with the discrete steps this enables a
> client to differ between line-based scrolling on a mouse wheel and smooth
> scrolling with a touchpad.
> 
> We can't extend the existing wl_pointer.axis events so we introduce a new
> concept: latching events. These events (axis_source and axis_discrete)
> are prefixed before a wl_pointer.axis or axis_stop event, i.e. the sequence
> becomes:
> 
> wl_pointer.axis_source
> wl_pointer.axis
> wl_pointer.axis_source
> wl_pointer.axis
> wl_pointer.axis_source
> wl_pointer.axis
> wl_pointer.axis_source
> wl_pointer.axis_stop
> 
> or:
> 
> wl_pointer.axis_source
> wl_pointer.axis_discrete
> wl_pointer.axis_axis
> 
> Clients need to combine the state of all events where needed.
> ---
> Changes to v2:
> - more documentation, should be self-explanatory now
> - drop time and axis values from the events where they are redundant
> - axis_stop now carries an array so we can end more axes in one go
> 
> wl_pointer.axis_discrete.discrete stayed an int after some IRC chat with
> Jonas. I've expanded the documentation a bit to hopefully make it clear this
> event won't be generated for some devices. Let's leave converting from
> pixel-space to discrete events up to the clients, they have more semantic
> knowledge of what exactly is required.
> 
>  protocol/wayland.xml | 98 +++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 94 insertions(+), 4 deletions(-)
> 
> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> index c5963e8..15f8d72 100644
> --- a/protocol/wayland.xml
> +++ b/protocol/wayland.xml
> @@ -1337,7 +1337,7 @@
>         wl_seat.get_keyboard or wl_seat.get_touch, the returned object is
>         always of the same version as the wl_seat.
>     -->
> -  <interface name="wl_seat" version="4">
> +  <interface name="wl_seat" version="5">
>      <description summary="group of input devices">
>        A seat is a group of keyboards, pointer and touch devices. This
>        object is published as a global during start up, or when such a
> @@ -1411,7 +1411,7 @@
>    </interface>
>  
>    <!-- for the version see the comment in wl_seat -->
> -  <interface name="wl_pointer" version="3">
> +  <interface name="wl_pointer" version="5">
>      <description summary="pointer input device">
>        The wl_pointer interface represents one or more input devices,
>        such as mice, which control the pointer location and pointer_focus
> @@ -1572,10 +1572,100 @@
>        <description summary="release the pointer object"/>
>      </request>
>  
> +    <!-- Version 5 additions -->
> +
> +    <enum name="axis_source">
> +      <description summary="axis source types">
> +	Describes the source types for axis events. This indicates to the

nit: Seems you have a tab here while not in the other paragraphs.

> +        client how an axis event was physically generated, a client may

nit: I'm not a native speaker, but shouldn't this be either a full stop
(.) or a semi colon (;), instead of a comma (,)?

> +        adjust the user interface accordingly. For example, scroll events
> +        from a "finger" source may be in a smooth coordinate space with
> +        kinetic scrolling whereas a "wheel" source may be in discrete steps
> +        of a number of lines.
> +
> +        The "continous" axis source is a device generating events in a
> +        continuous coordinate space, but using something other than a
> +        finger. One example for this source is button-based scrolling where
> +        the vertical motion of a device is converted to scroll events while
> +        a button is held down.
> +      </description>
> +      <entry name="wheel" value="0" summary="A physical wheel" />
> +      <entry name="finger" value="1" summary="Finger on a touch surface" />

Just thought about the ambiguity of using "finger" as one usually uses a
finger to scroll on a wheel. But whatever. Using "touch" would be rather
ambiguous too I suppose.

> +      <entry name="continuous" value="2" summary="Continuous coordinate space"/>
> +    </enum>
> +
> +    <event name="axis_source" since="5">
> +      <description summary="axis source event">
> +        Scroll and other axis source notification.
> +
> +        This event does not occur on its own. It is sent before a
> +        wl_pointer.axis or wl_pointer.axis_stop event and carries the source
> +        information for that event. A client is expected to accumulate the
> +        data in both events before proceeding.
> +
> +        The source specifies how this event was generated. If the source is
> +        wl_pointer.axis_source.finger, a wl_pointer.axis_stop event will be
> +        sent when the user lifts the finger off the device.
> +
> +        If the source is wl_pointer.axis_source.wheel or
> +        wl_pointer.axis_source.continuous, a wl_pointer.axis_stop event may
> +        be sent but is not guaranteed to be sent.
> +
> +        This event is optional. If the source is unknown for a particular
> +        axis event sequence, no event is sent.
> +
> +        The order of wl_pointer.axis_discrete and wl_pointer.axis_source is
> +        not guaranteed.
> +      </description>
> +      <arg name="axis_source" type="uint"/>
> +    </event>
> +
> +    <event name="axis_stop" since="5">
> +      <description summary="axis stop event">
> +        Scroll and other axis stop notification.
> +
> +        For some wl_pointer.axis_source types, a wl_pointer.axis_stop event
> +        is sent to notify a client that the axis sequence has terminated.
> +        This enables the client to implement kinetic scrolling.
> +        See the wl_pointer.axis_source documentation for information on when
> +        this event may be generated.
> +
> +        Any wl_pointer.axis events after this event should be considered as
> +        the start of a new axis motion.

Maybe should clarify thats its a stat of a new motion from the same
source type as was just stopped. A stopped finger touch, does not affect
the state of a ongoing continuous scroll.

> +
> +        The timestamp is to be interpreted identical to the timestamp in the
> +        wl_pointer.axis event.

It is unclear what axis event you are referring to here, as this is not
a latched state event. Maybe we should just "warn" that it may be identical
to the previous axis event of the same source type?

> +
> +        The axes array lists all axes stopped with this event.
> +      </description>
> +      <arg name="time" type="uint" summary="timestamp with millisecond granularity"/>
> +      <arg name="axes" type="array" summary="the axes stopped with this event"/>
> +    </event>
> +
> +    <event name="axis_discrete" since="5">
> +      <description summary="axis click event">
> +        Scroll and other axis discrete step information.

This sentence sounds odd. Maybe "Scroll and other discrete step information"?

Jonas

> +
> +        This event does not occur on its own. It is sent before a
> +        wl_pointer.axis event and carries the axis value of the
> +        wl_pointer.axis event in discrete steps (e.g. mouse wheel clicks).
> +
> +        This event is optional, continuous scrolling devices
> +        like two-finger scrolling on touchpads do not have discrete
> +        steps and do not generate this event.
> +
> +        The discrete value carries the directional information. e.g. a value
> +        of -2 is two steps towards the negative direction of this axis.
> +
> +        The order of wl_pointer.axis_discrete and wl_pointer.axis_source is
> +        not guaranteed.
> +        <arg name="discrete" type="int"/>
> +      </description>
> +    </event>
>    </interface>
>  
>    <!-- for the version see the comment in wl_seat -->
> -  <interface name="wl_keyboard" version="4">
> +  <interface name="wl_keyboard" version="5">
>      <description summary="keyboard input device">
>        The wl_keyboard interface represents one or more keyboards
>        associated with a seat.
> @@ -1690,7 +1780,7 @@
>    </interface>
>  
>    <!-- for the version see the comment in wl_seat -->
> -  <interface name="wl_touch" version="3">
> +  <interface name="wl_touch" version="5">
>      <description summary="touchscreen input device">
>        The wl_touch interface represents a touchscreen
>        associated with a seat.
> -- 
> 2.3.5
> 