[PATCHv4 wayland-protocols] text-input: Add v3 of the text-input protocol

Thu May 3 19:55:40 UTC 2018

On Thu, May 03, 2018 at 09:22:46PM +0200, Dorota Czaplejewicz wrote:
> On Thu, 3 May 2018 20:47:27 +0200
> Silvan Jegen <s.jegen at gmail.com> wrote:
> 
> > Hi Dorota
> > 
> > Some comments and typo fixes below.
> > 
> > On Thu, May 03, 2018 at 05:41:21PM +0200, Dorota Czaplejewicz wrote:
> > > This new protocol description is a simplification over v2.
> > > 
> > > - All pre-edit text styling is gone.
> > > - Pre-edit cursor can span characters.
> > > - No events regarding input panel (OSK) state nor covered rectangle.
> > >   Compositors are still free to handle situations where the keyboard
> > >   focus rectangle is covered by the input panel.
> > > - No set_preferred_language request for clients.
> > > - There is no event to send keysyms. Compositors can use wl_keyboard
> > >   interface instead.
> > > - All state is double-buffered, with specified state.
> > > - Use Unicode codepoints to measure strings.
> > > 
> > > Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz at puri.sm>
> > > Signed-off-by: Carlos Garnacho <carlosg at gnome.org>
> > > ---
> > > This is the next update coming from Purism to perfect the text input protocol.
> > > 
> > > The following changes added on top of PATCHv3:
> > > 
> > > - Fixed whitespaces.
> > > - Removed enable flags - the same information can be gathered from
> > > the first requests after enter.
> > > - Changed offsets inside UTF-8 strings to use Unicode character
> > > counts in order to remove the possibility of communicating invalid
> > > state.
> > > - Specified the exact lifetime of double-buffered state, and initial values.
> > > - Made changes requested by the IM double-buffered.
> > > 
> > > Some questions remain open. One is: how to specify how much text
> > > to capture in set_surrounding_text, and how often to update?
> > > 
> > > A possible change that I decided against for now is to replace
> > > enable/disable events by create/destroy of a new object, which
> > > would make more state lifetimes encoded in the protocol.
> > > 
> > > After reading a blog post on fcitx [0], I got the impression that
> > > letting the compositor know some persistent ID of a text edit
> > > instance could be useful, however I'm not sure what the use cases
> > > are.
> > > 
> > > As always, I'm happy to hear feedback.
> > > 
> > > Cheers,
> > > Dorota Czaplejewicz
> > > 
> > > [0] https://www.csslayer.info/wordpress/fcitx-dev/gaps-between-wayland-and-fcitx-or-all-input-methods/
> > > 
> > >  Makefile.am                                    |   1 +
> > >  unstable/text-input/text-input-unstable-v3.xml | 362 +++++++++++++++++++++++++
> > >  2 files changed, 363 insertions(+)
> > >  create mode 100644 unstable/text-input/text-input-unstable-v3.xml
> > > 
> > > diff --git a/Makefile.am b/Makefile.am
> > > index 4b9a901..86d7ca9 100644
> > > --- a/Makefile.am
> > > +++ b/Makefile.am
> > > @@ -3,6 +3,7 @@ unstable_protocols =								\
> > >  	unstable/fullscreen-shell/fullscreen-shell-unstable-v1.xml		\
> > >  	unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml			\
> > >  	unstable/text-input/text-input-unstable-v1.xml				\
> > > +	unstable/text-input/text-input-unstable-v3.xml				\
> > >  	unstable/input-method/input-method-unstable-v1.xml			\
> > >  	unstable/xdg-shell/xdg-shell-unstable-v5.xml				\
> > >  	unstable/xdg-shell/xdg-shell-unstable-v6.xml				\
> > > diff --git a/unstable/text-input/text-input-unstable-v3.xml b/unstable/text-input/text-input-unstable-v3.xml
> > > new file mode 100644
> > > index 0000000..ed5204f
> > > --- /dev/null
> > > +++ b/unstable/text-input/text-input-unstable-v3.xml
> > > @@ -0,0 +1,362 @@
> > > +<?xml version="1.0" encoding="UTF-8"?>
> > > +
> > > +<protocol name="text_input_unstable_v3">
> > > +  <copyright>
> > > +    Copyright © 2012, 2013 Intel Corporation
> > > +    Copyright © 2015, 2016 Jan Arne Petersen
> > > +    Copyright © 2017, 2018 Red Hat, Inc.
> > > +    Copyright © 2018 Purism SPC
> > > +
> > > +    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="zwp_text_input_v3" version="1">
> > > +    <description summary="text input">
> > > +      The zwp_text_input_v3 interface represents text input and input methods
> > > +      associated with a seat. It provides enter/leave events to follow the
> > > +      text input focus for a seat.
> > > +
> > > +      Requests are used to enable/disable the text-input object and set
> > > +      state information like surrounding and selected text or the content type.
> > > +      The information about the entered text is sent to the text-input object
> > > +      via the pre-edit and commit_string events.
> > > +
> > > +      Text is valid UTF-8 encoded, indices and lengths are in code points. If a
> > > +      grapheme is made up of multiple code points, an index pointing to any of
> > > +      them should be interpreted as pointing to the first one.  
> > 
> > That way we make sure we don't put the cursor/anchor between bytes that
> > belong to the same UTF-8 encoded Unicode code point which is nice. It
> > also means that the client has to parse all the UTF-8 encoded strings
> > into Unicode code points up to the desired cursor/anchor position
> > on each "preedit_string" event. For each "delete_surrounding_text" event
> > the client has to parse the UTF-8 sequences before and after the cursor
> > position up to the requested Unicode code point.
> > 
> > I feel like we are processing the UTF-8 string already in the
> > input-method. So I am not sure that we should parse it again on the
> > client side. Parsing it again would also mean that the client would need
> > to know about UTF-8 which would be nice to avoid.
> > 
> > Thoughts?
> 
> The client needs to know about Unicode, but not necessarily about
> UTF-8. Specifying code points is actually an advantage here, because
> byte offsets are inherently expressed relative to UTF-8. By counting
> with code points, client's internal representation can be UTF-16 or
> maybe even something else.

Maybe I am misunderstanding something but the protocol specifies that
the strings are valid UTF-8 encoded and the cursor/anchor offsets into
the strings are specified in Unicode points. To me that indicates that
the application *has to parse* the UTF-8 string into Unicode points
when receiving the event otherwise it doesn't know after which Unicode
point to draw the cursor. Of course the application can then decide to
convert the UTF-8 string into another encoding like UTF-16 for internal
processing (for whatever reason) but that doesn't change the fact that
it still would have to parse the incoming UTF-8 (and thus know about
UTF-8).

> There's no avoiding the parsing either. What the application cares
> about is that the cursor falls between glyphs. The application cannot
> know that in all cases. Unicode allows the same sequence to be
> displayed in multiple ways (fallback):
> 
> https://unicode.org/emoji/charts/emoji-zwj-sequences.html
> 
> One could make an argument that byte offsets should never be close
> to ZWJ characters, but I think this decision is better left to the
> application, which knows what exactly it is presenting to the user.

The idea of the previous version of the protocol (from my understanding)
was to make sure that only valid UTF-8 and valid byte-offsets (== not
falling between bytes of a Unicode code point) into the string will be
sent to the client. If you just get a byte-offset into a UTF-8 encoded
string you trust the sender to honor the protocol and thus you can just
pass the UTF-8 encoded string unprocessed to your text rendering library
(provided that the library supports UTF-8 strings which is what I am
assuming) without having to parse the UTF-8 string into Unicode code
points.

Of course the Unicode code points will have to be parsed at some point
if you want to render them. Using byte-offsets just lets you do that at
a later stage if your libraries support UTF-8.

Cheers,

Silvan
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