[PATCH 1/6] Add weston randr protocol
Pekka Paalanen
ppaalanen at gmail.com
Thu Feb 27 00:35:30 PST 2014
On Thu, 27 Feb 2014 08:06:23 +0000
"Wang, Quanxian" <quanxian.wang at intel.com> wrote:
>
>
> -----Original Message-----
> From: Pekka Paalanen [mailto:ppaalanen at gmail.com]
> Sent: Thursday, February 27, 2014 3:28 PM
> To: Wang, Quanxian
> Cc: wayland-devel at lists.freedesktop.org; Zhang, Xiong Y
> Subject: Re: [PATCH 1/6] Add weston randr protocol
>
> On Thu, 27 Feb 2014 11:28:00 +0800
> Quanxian Wang <quanxian.wang at intel.com> wrote:
>
> > Weston protocol wrandr will provide interface to
> > 1) set output mode
> > 2) set output transform
> > 3) move output to relative position
> > 4) provide disconnected display port information
> >
> > *Dynamic* mode setting is the main objective of this protocol.
> > Remember, it is one shot operation. For example, if setting the
> > mode, just call one request wl_randr_set_mode without any other
> > operation.
>
> Hi,
>
> like I said in my other reply, this is a configuration interface, not
> something for all applications to use. Protocol comments below
> assuming, that this will be a configuration interface and that the
> generic idea is acceptable.
>
> > Signed-off-by: Quanxian Wang <quanxian.wang at intel.com>
> > Reviewed-by: Zhang, Xiong Y <xiong.y.zhang at intel.com>
> > ---
> > protocol/Makefile.am | 1 +
> > protocol/randr.xml | 151
> > +++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files
> > changed, 152 insertions(+) create mode 100644 protocol/randr.xml
> >
> > diff --git a/protocol/Makefile.am b/protocol/Makefile.am index
> > 5e331a7..df2e070 100644
> > --- a/protocol/Makefile.am
> > +++ b/protocol/Makefile.am
> > @@ -5,6 +5,7 @@ protocol_sources = \
> > text.xml \
> > input-method.xml \
> > workspaces.xml \
> > + randr.xml \
> > text-cursor-position.xml \
> > wayland-test.xml \
> > xdg-shell.xml \
> > diff --git a/protocol/randr.xml b/protocol/randr.xml new file mode
> > 100644 index 0000000..f15e87a
> > --- /dev/null
> > +++ b/protocol/randr.xml
> > @@ -0,0 +1,151 @@
> > +<?xml version="1.0" encoding="UTF-8"?> <protocol name="randr">
> > +
> > + <copyright>
> > + Copyright (c) 2012-2013 Collabora, Ltd.
>
> Fix this.
>
> > +
> > + Permission to use, copy, modify, distribute, and sell this
> > + software and its documentation for any purpose is hereby
> > granted
> > + without fee, provided that the above copyright notice appear in
> > + all copies and that both that copyright notice and this
> > permission
> > + notice appear in supporting documentation, and that the name of
> > + the copyright holders not be used in advertising or publicity
> > + pertaining to distribution of the software without specific,
> > + written prior permission. The copyright holders make no
> > + representations about the suitability of this software for any
> > + purpose. It is provided "as is" without express or implied
> > + warranty.
> > +
> > + THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO
> > THIS
> > + SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
> > AND
> > + FITNESS, IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR
> > ANY
> > + SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
> > + WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
> > WHETHER IN
> > + AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
> > + ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
> > + THIS SOFTWARE.
> > + </copyright>
> > +
> > + <interface name="wl_randr" version="1">
> > + <description summary="randr">
> > + The global interface exposing randr capabilities.
> > + As a wl_randr, that provides the interfaces for apps to more
> > operations
> > + on output.
> > +
> > + The aim of wl_randr is to get modes list, choose preferred
> > mode,
> > + layout the output including position, rotate, and en/disable.
> > + The idea is from xrandr protocoal of xserver. It is very
> > convenient for
> > + weston/wayland user to operates on mode setting of output.
> > + </description>
> > +
> > + <enum name="error">
> > + <entry name="bad_randr" value="0"
> > + summary="the to-be wl_randr is invalid"/>
> > + </enum>
> > +
> > + <request name="destroy" type="destructor">
> > + <description summary="unbind from the wl_randr interface">
> > + Informs the server that the client will not be using this
> > + protocol object anymore. This does not affect any other
> > + objects, wl_randr objects included.
> > + </description>
> > + </request>
> > +
> > + <request name="set_mode">
> > + <description summary="set the mode of output">
> > + set the mode of output
> > + </description>
> > + <arg name="output" type="object" interface="wl_output"
> > + summary="the output object"/>
> > + <arg name="width" type="int"/>
> > + <arg name="height" type="int"/>
> > + <arg name="refresh" type="int"/>
> > + </request>
>
> Since you require a wl_output, there does not seem to be a way to
> force a disconnected output on? Should there be? Why else would you
> need a way to list disconnected outputs? [Wang, Quanxian] list
> disconnected outputs, just let user get to know the status of display
> port in this current machine. Who are connected, who are not
> connected.
>
> Should there be a way to force a connected output off?
>
> What about detailed mode timings? Should the client be allowed to use
> e.g. CVT or GTF formulae to invent completely new modes that the
> hardware might support? [Wang, Quanxian] wl_out or mode will be
> firstly be available in compositor. Otherwise, this interface will
> not allow that. We will check the parameter to make sure if user sets
> it rightly or under the control.
>
> > +
> > + <request name="set_transform">
> > + <description summary="set the transform of output">
> > + set the transform of output
> > + </description>
> > + <arg name="output" type="object" interface="wl_output"
> > + summary="the output object"/>
> > + <arg name="transform" type="uint"
> > + summary="the value should be between 0-7"/>
> > + </request>
> > +
> > + <enum name="move">
> > + <description summary="move target output to the position of
> > source output">
> > + The purpose is mainly to allow clients move target output
> > to
> > + the position of source output.
> > + </description>
> > + <entry name="rightof" value="0"/>
> > + <entry name="leftof" value="1"/>
> > + </enum>
> > +
> > + <request name="move">
> > + <description summary="move target output">
> > + position the target output leftof/rightof source output
> > + </description>
> > + <arg name="target_output" type="object" interface="wl_output"
> > + summary="the target output object"/>
> > + <arg name="source_output" type="object" interface="wl_output"
> > + summary="the source output object"/>
> > + <arg name="move" type="int"/>
> > + </request>
>
> Let's say I want to change a mode and move an output to another side.
> How would I do that atomically? I mean, without the compositor e.g.
> [Wang, Quanxian] live with compositor.
>
> first showing me the output on the other side in original mode, and
> then switches the mode to what I asked for. [Wang, Quanxian] :).
> Currently we don't support complex command in one shot. The request
> is an atomic action. If you want to do that, just first change mode,
> and then call another atomic operation to move.
>
> How do I do many operations, perhaps on multiple outputs, in a single
> shot without flickering or glitches? [Wang, Quanxian] The above.
IOW, I just cannot.
Atomicity is not easy to add as an afterthought. If there is any
possibility that it would be needed, it should be designed in from the
start. There are several examples where adding atomic group operations
just cannot work with the original interface, which means you get a new
interface and have to maintain both, or you break the old interface
which might not be possible.
> > +
> > + <request name="get_disoutputs">
> > + <description summary="disconnected output information">
> > + get the disconnected display port information
> > + </description>
> > + </request>
>
> It seems you have modeled this interface like a function call API.
> Function calls are synchronous and built on roundtrips (return
> values), while Wayland protocol is the exact opposite. [Wang,
> Quanxian] Right. But I just want to get the information from
> compositor instead of from drm or others. It lives with compositor.
>
> You could design a protocol, where the list of disconnected outputs
> is kept up to date automatically by the compositor just sending
> events when a client a) binds to the global interface, and b) when
> connector status changes. That could include also connected
> outputs/connectors. [Wang, Quanxian] Yes. Good idea.
>
> > + <request name="get_output_name">
> > + <description summary="output name">
> > + get the output name
> > + </description>
> > + <arg name="wl_output" type="object" interface="wl_output"/>
> > + </request>
>
> Yeah, would be better as a wl_output event indeed.
> [Wang, Quanxian] core protocol is not easy to be changed. :)
This is about adding a new event to a core interface. We have mechanisms
to do that without breaking anything. It "just" needs to be well-thought
and well-designed.
>
> > +
> > + <event name="output_name">
> > + <description summary="output name">
> > + get output name of wl_output
> > + </description>
> > + <arg name="output" type="object" interface="wl_output"/>
> > + <arg name="name" type="string"/>
> > + </event>
> > +
> > + <enum name="action">
> > + <description summary="action">
> > + Actions have been taken.
> > + </description>
> > + <entry name="move" value="0"/>
> > + <entry name="transform" value="1"/>
> > + <entry name="mode" value="2"/>
> > + </enum>
> > +
> > + <enum name="result">
> > + <description summary="action result">
> > + Action result
> > + </description>
> > + <entry name="FAIL" value="-1"/>
> > + <entry name="SUCCESS" value="1"/>
> > + <entry name="NOACT" value="2"/>
> > + </enum>
> > +
> > + <event name="action_done">
> > + <description summary="action done event">
> > + Notify the randr client mode set done.
> > + </description>
> > + <arg name="flags" type="uint"
> > + summary="which action is done"/>
> > + <arg name="result" type="int"/>
> > + </event>
>
> If I change the mode on two different outputs, how do I know which
> action_done corresponds to which request? [Wang, Quanxian] right, add
> wl_output parameter.
No. If I do two mode set operations on the same wl_output, then again I
would not know which answer was for which.
Instead, a generic pattern for this kind of "return data" is to let the
original request also create a feedback protocol object. This object is
unique to the request that was sent, and can deliver any return data
without any ambiguity. An example of a feedback object is wl_callback,
except it can only deliver "done", not "yes"/"no"; not delivering
anything will cause problems.
>
> What if move succeeds but mode change fails? Wouldn't that leave the
> output in an unwanted state which is neither the original nor the
> wanted setting? [Wang, Quanxian] one by one. Not support complex. If
> you have such case, have to turn back. Call another move back. But
> firstly make sure the previous is successful.
That will require a lot of roundtrips, and it essentially forces the
compositor to show all the intermediate steps on the monitors. IOW,
that is designed to be both slow and glitchy. That's not how you should
do dynamic mode setting. I think you are going to need atomic group
operations.
> The solution to this would tie in with the solution to take changes
> atomic. For instance, to prepare for a configuration change, one
> might create a change object in the protocol, store all changes in
> that object, and then commit that set of changes atomically. Then
> have one return value: the whole set either succeeds or fails.
>
> I guess you could look for inspiration in the DRM atomic mode setting
> API. I don't know how the RandR X11 protocol works, if that would be
> a good example also.
Thanks,
pq
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