[PATCH weston v3 1/5] protocol: Add _wl_pointer_gestures (swipe/pinch) protocol

[Bill Spitzak]

On Fri, Jul 31, 2015 at 6:59 AM, Carlos Garnacho <carlosg at gnome.org> wrote:

>
> +    <event name="update">
> +      <description summary="multi-finger pinch motion">
> +       This event is sent when a multi-finger pinch gesture changes the
> +       position of the logical center, the rotation or the relative scale.
> +
> +       The dx and dy coordinates are relative coordinates in the
> +       surface coordinate space of the logical center of the gesture.
> +
> +       The scale factor is an absolute scale compared to the
> +       pointer_gesture_pinch.begin event, e.g. a scale of 2 means the
> fingers
> +       are now twice as far apart as on pointer_gesture_pinch.begin.
> +
> +       The rotation is the relative angle in degrees clockwise compared
> to the previous
> +       pointer_gesture_pinch.begin or pointer_gesture_pinch.update event.
> +      </description>
> +      <arg name="time" type="uint" summary="timestamp with millisecond
> granularity"/>
> +      <arg name="dx" type="fixed" summary="delta x coordinate in surface
> coordinate space"/>
> +      <arg name="dy" type="fixed" summary="delta y coordinate in surface
> coordinate space"/>
> +      <arg name="scale" type="fixed" summary="scale relative to the
> initial finger position"/>
> +      <arg name="rotation" type="fixed" summary="angle in degrees cw
> relative to the previous event"/>
> +    </event>


This is something that would have to be changed in libinput, but it would
be a lot easier on clients if the data was consistently relative to the
initial begin event, rather than the scale being relative to the begin
event while the rotation is relative to the previous event. Also it would
be nice if the rotation was counter-clockwise as that is what positive
angles mean in most graphics libraries.
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