[UPDATED PATCH wayland] protocol: Add a request and event to identify the visible area for a surface

[Bill Spitzak]

Rob Bradford wrote:
> From: Rob Bradford <rob at linux.intel.com>
> 
> Add a probe_area request to the wl_shell_surface interface along with a
> visible_area event to communicate the result of the probe.
> 
> The intention of this request and event is to allow the client to try and
> refine the placement of popup windows that would otherwise be unusable.
> ---
>  protocol/wayland.xml | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> index edb8a03..023067a 100644
> --- a/protocol/wayland.xml
> +++ b/protocol/wayland.xml
> @@ -874,6 +874,46 @@
>  	to the client owning the popup surface.
>        </description>
>      </event>
> +
> +    <request name="probe_area">

I think this needs to take the extra argument that popup takes, which is 
used to determine if the window is above/below the panel.

> +      </description>
> +      <arg name="x" type="int"/>
> +      <arg name="y" type="int"/>
> +      <arg name="width" type="int"/>
> +      <arg name="height" type="int"/>
> +      <arg name="result" type="new_id" interface="wl_probe_result"/>
> +    </request>
> +  </interface>
> +
> +  <interface name="wl_probe_result" version="1">
> +    <event name="visible_area">
> +      <description summary="the area that would be visible for a proposed transient surface">
> +        This event is fired in response to the probe_area request on the
> +        object returned for that request. It returns the visible area that
> +        the surface would occupy when taking into consideration the
> +        output's edges. If the width or height is zero this indicates that the
> +        window would not be visible at all in that dimension. In that case the
> +        x and y values represent the distance to the edge of the viewable
> +        area.

May want to either say that negative sizes indicate empty, or that 
negative sizes are not allowed to be returned. Basically I think it 
should be the shell's responsibility to return positive width and height.

In your sample implementation the x/y is the maximum of the top-left of 
the visible area and the top-left of the rectangle passed to the 
request. Your intention to return the nearest point on the edge of the 
visible rectangle is a good one, however.

I think you better check what the sample implementation does for rotated 
outputs. Arbitrary transforms are a pain. IMHO the caller does not 
literally want the unclipped rectangle and a rectangle with the same 
area and center and matching for 90 degree rotations will work and 
popups will appear pretty good on rotated clients. This (assuming I 
extracted it correctly from some sample code I had) returns the 
rectangle for the affine transform matrix (ac0,bd0,XY1):

   w' = hypot(aw,ch)
   h' = hypot(bw,dh)
   x' = a(x+w/2)+c(y+h/2)+X-w'/2
   y' = b(x+w/2)+d(y+h/2)+Y-h'/2