[PATCH weston v4 01/15] Add a fullscreen shell protocol

[Bryce W. Harrington]

On Tue, Feb 25, 2014 at 07:26:33PM -0600, Jason Ekstrand wrote:
> Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
> ---
>  protocol/fullscreen-shell.xml | 158 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 158 insertions(+)
>  create mode 100644 protocol/fullscreen-shell.xml
> 
> diff --git a/protocol/fullscreen-shell.xml b/protocol/fullscreen-shell.xml
> new file mode 100644
> index 0000000..13bdfcf
> --- /dev/null
> +++ b/protocol/fullscreen-shell.xml
> @@ -0,0 +1,158 @@
> +<protocol name="fullscreen_shell">
> +  <interface name="wl_fullscreen_shell" version="1">
> +    <description summary="Displays a single surface per output">
> +      Displays a single surface per output.
> +
> +      This interface provides a mechanism for a single client to display
> +      simple full-screen surfaces.  While there technically may be multiple
> +      clients bound to this interface, only one of those clients should be
> +      shown at a time.
> +
> +      To present a surface, the client uses either the present_surface or
> +      present_surface_for_mode requests.  Presenting a surface takes effect
> +      on the next wl_surface.commit.  See the individual requests for
> +      details about scaling and mode switches.
> +      
> +      The client can have at most one surface per output at any time.
> +      Requesting a surface be presented on an output that already has a
> +      surface replaces the previously presented surface.  Presenting a null
> +      surface removes its content and effectively disables the output.
> +      Exactly what happens when an output is "disabled" is
> +      compositor-specific.  The same surface may be presented multiple

presented to multiple

> +      outputs simultaneously.
> +
> +      Once a surface is presented on an output, it stays on that output
> +      until either the client removes it or the compositor destroys the
> +      output.  This way, the client can update the output's contents by
> +      simply attaching a new buffer.
> +    </description>
> +
> +    <request name="release" type="destructor">
> +      <description summary="release the wl_fullscreen_shell interface">
> +      	Release the binding from the wl_fullscreen_shell interface
> +
> +	This destroys the server-side object and frees this binding.  If
> +	the client binds to wl_fullscreen_shell multiple times, it may wish
> +	to free some of those bindings.
> +      </description>
> +    </request>
> +
> +    <enum name="present_method">
> +      <description summary="different method to set the surface fullscreen">
> +	Hints to indicate to the compositor how to deal with a conflict
> +	between the dimensions of the surface and the dimensions of the
> +	output. The compositor is free to ignore this parameter.
> +      </description>
> +      <entry name="default" value="0" summary="no preference, apply default policy"/>
> +      <entry name="center" value="1" summary="center the surface on the output"/>
> +      <entry name="zoom" value="2" summary="scale the surface, preserving aspect ratio, to the largest size that will fit on the output" />
> +      <entry name="zoom_crop" value="3" summary="scale the surface, preserving aspect ratio, to fully fill the output cropping if needed" />
> +      <entry name="stretch" value="4" summary="scale the surface to the size of the output ignoring aspect ratio" />
> +    </enum>
> +
> +    <request name="present_surface">
> +      <description summary="present surface for display">
> +	Present a surface on the given output.
> +
> +	If the output is null, the compositor will present the surface on
> +	whatever display (or displays) it thinks best.  In particular, this
> +	may replace any or all surfaces currently presented so it should
> +	not be used in combination with placing surfaces on specific
> +	outputs.
> +
> +	The method parameter is a hint to the compositor for how the surface
> +	is to be presented.  In particular, it tells the compostior how to
> +	handle a size mismatch between the presented surface and the
> +	output.  The compositor is free to ignore this parameter.
> +
> +	The "zoom", "zoom_crop", and "stretch" methods imply a scaling
> +	operation on the surface.  This will override any kind of output
> +	scaling, so the buffer_scale property of the surface is effectively
> +	ignored.
> +      </description>
> +      <arg name="surface" type="object" interface="wl_surface" allow-null="true"/>
> +      <arg name="method" type="uint"/>
> +      <arg name="output" type="object" interface="wl_output" allow-null="true"/>
> +    </request>
> +
> +    <request name="present_surface_for_mode">
> +      <description summary="present surface for display at a particular mode">
> +	Presents a surface on the given output for a particular mode.
> +
> +	If the current size of the output differs from that of the surface,
> +	the compositor will attempt to change the size of the output to
> +	match the surface.  The result of the mode-swith operation will be

mode-switch

> +	returned via the provided wl_fullscreen_shell_mode_feedback object.
> +
> +	If the current output mode matches the one requested or if the
> +	compositor successfully switches the mode to match the surface,
> +	then the mode_successfull event will be sent and the output will

mode_successful event

> +	contain the contents of the given surface.  If the compositor
> +	cannot match the output size to the surface size, the mode_failed
> +	will be sent and the output will contain the contents of the
> +	previously presented surface (if any).  If another surface is
> +	presented on the given output before either of these has a chance
> +	to happen, the present_canceled event will be sent.

present_cancelled

Grepping weston for 'canceled' vs. 'cancelled' seems to indicate the
latter spelling is preferred.

> +	If the size of the presented surface changes, the resulting output
> +	is undefined.  The compositor may attempt to change the output mode
> +	to compensate.  However, there is no guarantee that a suitable mode
> +	will be found and the client has no way to be notified of success
> +	or failure.

Probably a stupid question but could the presented surface be locked to
prevent it from changing size?

> +	The framerate parameter specifies the target framerate for the
> +	output.  The compositor is free to ignore this parameter.  A value
> +	of 0 indicates that the client has no preference.

This doesn't actually define what the framerate parameter does.  Does it
do something if the framerate drops too low?  Or does it cap it to not
go above a certain level?

> +	If the surface has a buffer_scale greater than 1, the compositor
> +	may choose a mode that matches either the buffer size or the
> +	surface size.  In either case, the surface will fill the output.

This paragraph is a bit confusing.  Is buffer_scale a scaling factor?

> +      </description>
> +      <arg name="surface" type="object" interface="wl_surface"/>
> +      <arg name="output" type="object" interface="wl_output"/>
> +      <arg name="framerate" type="int"/>
> +      <arg name="feedback" type="new_id" interface="wl_fullscreen_shell_mode_feedback"/>
> +    </request>
> +
> +    <enum name="error">
> +      <description summary="wl_fullscreen_shell error values">
> +	These errors can be emitted in response to wl_fullscreen_shell requests
> +      </description>
> +      <entry name="invalid_method" value="0" summary="present_method is not known"/>
> +    </enum>
> +  </interface>
> +
> +  <interface name="wl_fullscreen_shell_mode_feedback" version="1">
> +    <event name="mode_successful">
> +      <description summary="mode switch succeeded">
> +	This event indicates that the attempted mode switch operation was
> +	successful.  A surface of the size requested in the mode switch
> +	will fill the output without scaling.
> +
> +	Upon recieving this event, the client should destroy the
receiving

> +	wl_fullscreen_shell_mode_feedback object.
> +      </description>
> +    </event>
> +    <event name="mode_failed">
> +      <description summary="mode switch failed">
> +	This event indicates that the attempted mode switch operation
> +	failed. This may be because the requested output mode is not
> +	possible or it may mean that the compositor does not want to allow
> +	mode switches at this time.

Would it be worth returning these two failure modes as distinct events?
Might help client developers in debugging if nothing else.

If lets say a game client wanted to do a mode change, would it make
sense for them to do a series of present_surface_for_mode calls and
keep trying different modes while they receive mode_failed events?
Or is there a way for them to query for allowed modes that they can
select from?

> +
> +	Upon recieving this event, the client should destroy the
receiving

> +	wl_fullscreen_shell_mode_feedback object.
> +      </description>
> +    </event>
> +    <event name="present_canceled">
present_cancelled

> +      <description summary="mode switch canceled">
mode switch cancelled

> +	This event indicates that the attempted mode switch operation was
> +	canceled.  Most likely this is because the client requested a
cancelled

> +	second mode switch before the first one completed.
> +
> +	Upon recieving this event, the client should destroy the
receiving

> +	wl_fullscreen_shell_mode_feedback object.
> +      </description>
> +    </event>
> +  </interface>
> +</protocol>
> -- 
> 1.8.5.3
> 
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Apart from a few typos here and there, the docs are very coherent and
understandable.  

Reviewed-by: Bryce Harrington <b.harrington at samsung.com>

Bryce