[gnu-emacs] / README.xwidget

* Xwidgets

This is an experimental branch to enable embedding of GTK widgets
inside an Emacs window. The Emacs abstraction is called an Xwidget,
for eXternal widget, and also in reference to the Xembed protocoll.

There is a demo file called xwidget-test.el which shows some of the
possibilities. There are some screnshots at the emacswiki.

Currently its possible to insert buttons, sliders, and xembed widgets
in the buffer. It works similar to the support for images in Emacs.
Adding more types of widgets should be fairly straightforward, but
will require adapter code for each type.

A difference from images is that xwidgets live their own life. You
create them with an api, get a reference, and tie them to a particular
buffer with a display spec. 

Each xwidget can have several views. In MVC terms, an xwidget is the
model, and an xwidget-view is a view of the xwidget in a particular
Emacs window.

The xwidget code attempts to keep the visual appearance of the views
in sync with through an Observer pattern implementation.

** building
bzr co bzr+ssh://bzr.savannah.gnu.org/emacs/xwidget/
export CFLAGS=" -g -DGLYPH_DEBUG=1"
#export CFLAGS="-g"
./configure   --with-x-toolkit=gtk3 --with-xwidgets
make -j4

** MVC and Xembedd
The MVC approach appears to be at least in principle robust for plain gtk
widgets. For the interesting case of gtk sockets which implements an
xembed host widget that allows for embedding other applications inside
an Emacs window, the story gets more complex.

The problem is that xembed is designed to plug an application window
inside a a secket and thats it. You can't move a plug between
sockets. I tried numerous hacks to get around this but there is
nothing that works realy well.

Therefore the Emacs part of the code will only expose well-defined
interfaces. cooperating applications will be able to use the interface
in a well defined manner. The problem is that there is no known xembeddable
application that implement the needed type of functionality, which is
allowing for creating new windows on the fly that plug into new
sockets.

Therefore I will attempt to provide an external application that wraps
another application and through hacks attempts to provide the needed
multi view xembed function. That way Emacs is sane and the insanity
contained.

This app will work by providing a socket that an app plugs into. The
socket window is copied efficientlp by means of composition to a
number of other windows, that then are plugged into the different
Emacs sockets. 

* Brief overview of how xwidgets work
Xwidgets work in one way like images in Emacs. You bind a display spec very
similar to an image display spec to buffer contents. The display engine will
notice the display spec and try to display the xwidget there. The display engine
prepares space at the right place for the xwidget and so on for free, as long as
we provide proper sizes and so on back to the redisplay engine.

** Issues
The problem is that Emacs cant actually draw the widgets, as it can with
images. Emacs must notify GTK about where the widgets should be, and how they
should be clipped and so on, and this information must be given to GTK
synchonous with Emacs display changes. Ok, so why is that difficult then?

- How do we know when a widget is NOT to be drawn? The only way I found so far
  is having a flag for each xwdiget, that is reset before a redisplay. When an
  xwidget is encountered during display, the flag is set. After redisplay,
  iterate all xwidgets and hide those which hasnt been displayed. 

- The gtk socket type for embedding external applications is desirable
  but presents a lot of difficulties of its own. One difficulty is
  deciding which input events to forward, and when and how to do it.

** placement and clipping
the entire emacs frame is a gtk window. we use the fixed layout
manager to place xwidgets on the frame. coordinates are supplied by
the emacs display engine. widgets are placed inside an intermediate
window, called the widgetwindow. the widgetwindows are placed on the
emacs frame.

this way was chosen to simplify clipping of the widgets against emacs
window borders.


** different strategies
Integrating toolkit widgets(gtk in this case) and the emacs display
engine is more difficult than your plain average gui application, and
different strategies has been tested and will continue to be tested.

There was a distinction between live xwidgets and
phantom xwidgets, previous to the change to MVC.

- the first aproach was to have the live xwidget on-screen, and move
  them about. the phantoms were generated by snapshoting the live
  xwidget. 

the drawback of that aproach was that the gtk toolkit is admirably
lazy and doesnt draw the widget if its not actualy shown, meaning that
the snapshots for the phantoms will show garbage.

- the second aproach was to use composition support. that tells gtk
  that the widget should be drawn in an off-screen buffer and drawn on
  screen by the application.

this has the primary advantage that the snapshot is always
available, and enables the possibility of more eye-candy like drawing
live and phantom widgets in different colors.

the drawback is that its our own responsibility to handle drawing,
which puts more of the display optimization burden on us.

this is aproach worked so-so.

- another aproach is to have both live and phantom widgets drawn
  on-screen by proxy gtk objects. the live xwidget will be entirely
  handled in an off-screen window, and the proxy objects will redirect
  events there.

- combine on-screen and off-screen aproaches. maybe composition is the
  way to go for most cases, but on-screen xembeding is the way to go
  for particular special cases, like showing video in a
  window. off-screen rendering and whatnot, is not efficient in that
  particular case, and the user will simply have to accept that the
  phantom of a video widget isnt particularily beautiful.

- The current and seemingly sanest aproach implements a MVC pattern.

** Testing
;;test like:
;; cd /path/to/xwidgets-emacs-dir
;; make   all&&  src/emacs -q --eval "(progn (load \"`pwd`/lisp/xwidget-test.el\") (xwidget-demo-basic))"

* ToDo:s
** DONE webkit flashkiller by default
   CLOSED: [2011-07-19 Tue 14:27]
while its possible to support plugins in the webkit xwidget, flash has
issues on 64 bit, and slows down emacs to a halt with off screen
rendering, and of course is not free software. its in the way for real
world usage even if its interesting to watch flash animations inside
emacs. which should be achieved with Gnash or other free software
instead.

http://stackoverflow.com/questions/4885513/prevent-flash-in-cocoa-webview

simply use this api:
http://webkitgtk.org/reference/WebKitWebPluginDatabase.html

** DONE allow xwidgets to report thoir size
   CLOSED: [2011-07-19 Tue 14:26]
now we just hard code sizes. but webkit widgets for instance can
report sizes that suit the content. support that.
** TODO BUG xwidget view ghosts
- xwidget-webkit-browse-url somewhere
- split window.
now theres 2 webkit views
- c-x 1
now theres 2 views but one is a ghost!
one should have been deleted when its window died but that didnt work
for some reason here.

- m-x xwidget-cleanup

the ghost goes away because we killed explicitly but this is just a workaround.

xwidget_view_delete_all_in_window(w); in delete-window-internal is not sufficient.
delete-other-windows-internal
delete_all_subwindows
unshow_buffer

** DONE BUG annoying backtrace
   CLOSED: [2011-07-19 Tue 14:28]
(this no longer seems to happen even under heavy usage. seems merging
from trunk helped. lots were happening in redisplay at this time in trunk.)

sadly happens a lot.
- happens even with no initialized xwidgets
-                    + row->glyphs[area][i].face_id
or similar code, so row is invalid for some reason.
xwidgets currently disable some redisplay opimizations so it might be
an actual emacs bug manifesting without optimizations.

*** bt 1
      /* Compute the width of this line.  */
      row->pixel_width = row->x;
      for (i = 0; i < row->used[TEXT_AREA]; ++i)
        row->pixel_width += row->glyphs[TEXT_AREA][i].pixel_width;

(gdb) bt
#0  0x000000000045c340 in compute_line_metrics (it=0x7fffffff8a20)
    at xdisp.c:17549
#1  0x00000000004603da in display_line (it=0x7fffffff8a20) at xdisp.c:18792
#2  0x0000000000457646 in try_window (window=23403045, pos=..., flags=1)
    at xdisp.c:15399
#3  0x00000000004559c9 in redisplay_window (window=23403045, just_this_one_p=0)
    at xdisp.c:14944
#4  0x0000000000450247 in redisplay_window_0 (window=23403045) at xdisp.c:13152
#5  0x00000000005fdcd9 in internal_condition_case_1 (bfun=
    0x450208 <redisplay_window_0>, arg=23403045, handlers=12691046, hfun=
    0x4501d9 <redisplay_window_error>) at eval.c:1538
#6  0x00000000004501ba in redisplay_windows (window=23403045) at xdisp.c:13132
#7  0x000000000044f19c in redisplay_internal () at xdisp.c:12706
#8  0x000000000044f9f2 in redisplay_preserve_echo_area (from_where=7)
    at xdisp.c:12964
#9  0x0000000000568525 in swallow_events (do_display=1) at keyboard.c:4197
#10 0x0000000000422554 in sit_for (timeout=40, reading=1, do_display=1)
    at dispnew.c:5963
#11 0x000000000056512c in read_char (commandflag=1, nmaps=8, maps=
    0x7fffffffd3f0, prev_event=12720514, used_mouse_menu=0x7fffffffd604, 
    end_time=0x0) at keyboard.c:2689
#12 0x0000000000572c59 in read_key_sequence (keybuf=0x7fffffffd850, bufsize=
    30, prompt=12720514, dont_downcase_last=0, can_return_switch_frame=1, 
---Type <return> to continue, or q <return> to quit---
    fix_current_buffer=1) at keyboard.c:9291
#13 0x0000000000562897 in command_loop_1 () at keyboard.c:1446
#14 0x00000000005fdb52 in internal_condition_case (bfun=
    0x5624b4 <command_loop_1>, handlers=12772898, hfun=0x561dab <cmd_error>)
    at eval.c:1493
#15 0x00000000005621ab in command_loop_2 (ignore=12720514) at keyboard.c:1157
#16 0x00000000005fd4ce in internal_catch (tag=12768770, func=
    0x562185 <command_loop_2>, arg=12720514) at eval.c:1247
#17 0x000000000056215e in command_loop () at keyboard.c:1136
#18 0x00000000005618f9 in recursive_edit_1 () at keyboard.c:757
#19 0x0000000000561a95 in Frecursive_edit () at keyboard.c:821
#20 0x000000000055fba2 in main (argc=1, argv=0x7fffffffe188) at emacs.c:1704


*** bt 2

** DONE Examine using XComposite rather than GTK off-screen
  rendering. This would make xembed widgets work much better. This
  would probably be rathter difficult, but could open up other
  interesting possibilities for Emacs. There is an early attempt in
  xwidget.c, but the X call to redirect to offscreen rendering fails
  for unknown reasons.

  the attempt was further worked on, and the xlib calls replaced with
  gdk calls, this works better.

** TODO  make the keyboard event code propagation code work. 
There is an attempt to provide an api to send keyboard events to an
xwidget, but it doesnt currently work very well.

try gtk event creation instead since that works fine in the webkit osr code.

** DONE remove the special-case for when the minibuffer is
  active.  I added some code to reduce the annoying problem display artefacts
  when making the minibuffer the selected window. This made xwidgets in the
  buffer go grey or black whenever one did m-x to activate the minibuffer. The
  coded tried to handle the minibuffer as a special case. That simply wasnt a
  good idea. Special-casing will never work properly. It is much better to spend
  time finding solutions that work acceptably in the general case.

** DONE disable emacs cursor drawing on top of an active xwidget. 
  This ought to be rather simple and should improve the visuals a lot.

** TODO  improve the xwidgets programming interface 
so its less of hand-waving affair. This shouldnt be too hard, but I
  have deliberatley not spent any time on it, since getting the
  visuals right is much harder. Anyway, I sort of think the interface
  should be somewhat like it is, except symbols is used instead of
  integers.
*** DONE use symbols for xwidget types rather than ints
    CLOSED: [2011-06-27 Mon 12:52]


*** TODO better lisp based structure for xwidgets
the lisp interface woud be like this:
- make-xwidget returns an xwidget object, similar to a process
  object. this object is used when creating the display spec(instead of
  the user defined id now used)

the data structure would be something like this:
- a "process" like aproach to create the xwidgets. xwidgets are
  coupled to buffers, somewhat like processes, except a buffer can
  hold several xwidgets
- an xwidget has a plist to hold the model, like a process
- an xwidget has an assoc list of xwidget views

there are some things that arent clear:
- an xwidget doesnt necessarily need to be coupled to a buffer but it
  seems to be the clearest model. xwidgets would be buffer local
- xwidget-views are by necessity coupled to a emacs window so it might
  be better to store them window locally rather than in an assoc
  coupled to the xwidget model
- for some gtk widgets that resist an mvc approach, like the webkit
  widgets, special operations are needed, similar to the old phantom
  widgets aproach. so we need to differentiate live and phantom
  instances for these troublesome widgets and let lisp manage all the trickery.

stuff that needs to work:
- do something for all views of a xwidget(resize, value change)
- do something for all xw-views in an emacs window(deletion etc)
- lookup xw-view for xwidget in emacs window(during redisplay)
(- do something for all siblings of a xw-view. not atm)

*** DONE xwidget creation interface
    CLOSED: [2011-07-18 Mon 01:59]
xwidgets are a little bit like emacs processes but also a little bit
like emacs images. Therefore its not perfectly obvious how to handle
creation. Currently I just use hardcoded identifiers. the real scheme
needs to be something else.

Heres a tentative approach:
- xwidget-create returns a xwidget object, like process creation
  functions. the xwidget will be largely uninitialized until
  discovered by redisplay. an xw belongs to a buffer
- xwidget-insert inserts the xwidget in a buffer. when discovered by
  redisplay it will be initialized and a xwidget-view allocated
- an event will be emitted when initialization is finished when
  relevant like for sockets

the problem with this aproach is that its not really legal to reuse
xwidget objects by writing several display specs who reference the
same xwidget. It could presumably be done but it would just become
weird for no real benefit. the big preblem is that the display spec
decides the on-screen size, and its not sane to have xwidget views
with different sizes. therefore such display specs would need to be
catched and dissallowed. Except it is hard because AFAIK the specs
don't have an identity as such. A flag in the structure could be set
by lookup so the first display attempt would win. but then you can't
rewrite the spec to change the size. hmmm. A third approach would be
to just allow the 1st spec refering an xw during a redisplay to take
effect, the rest are signaled as errors. this wouldnt be too bad.

the other aproach would be to work more like images:

- write the display spec with all information needed to create the
  xwidget.
- retrieve the xwidget objet from the spec with an xwidget-at-point function. It
  can be uninitalized which client code must handle. Unlike
  assynchronous process creation we dont get back a handle, because
  there is none yet.
- emitted event on initialization, when needed. Many widgets don't
  need this. for instance, a button sends an event when pressed. but
  you can't press it unless its on screen, and then its initialized
  properly. 

This approach seemed good, but how do I know which instance
generates an event if I cant set the id beforehand?

so, therefore, the first two aproach is used. 


*** DONE xwidget creation interface actually
    CLOSED: [2011-07-18 Mon 01:59]
conclusion of above ramblings:
- should be similar to make-text-button
- don't init from display spec, instead during make-xwidget call
*** TODO callbacks would be nice 
but they need to be handled initially with events for technical
reasons. C code can't call Lisp easily. The event handler can call the
callback though.

** TODO  more documentation
There should be user docs, and xwidget contributor docs. The current README
is all contributor docs there is now, apart from the code.



** CANCELLED look into more ways of displaying xwidgets, like binding them to a
   CLOSED: [2011-07-05 Tue 11:34]
window rather than a point in a buffer. This was suggested by Chidong.
This would be a useful addition to Emacs in itself, and would avoid nearly all 
display issues. I still think the general case is more interesting, but this
special case should also be added. The xwidget would then be bound to
replace the view of a particular window, and it would only show in
that window.

I got the webkit xwidget to work well enough so I dont see the need
for this now, except for sockets and I think it can better be dealt
with at the lisp level.

** DONE MVC mode for xwidgets
   CLOSED: [2011-06-27 Mon 12:53]
It appears unfruitful to chase using the same display mode for all
types of xwidgets. Composition is fun but not robust the way I'm
tried to do it.

Instead there should be a set of MVC xwidgets. Each on-screen instance
of an MVC widget would be a real GTK widget. The instances would
communciate state using signals. 

There are drawbacks. There is no inbuilt support for MVC in GTK, so we
have to roll our own, which is tedious if not much work for the few
cases.

MVC for xembedded application will need support from the applications
themselves. Inkscape supports multiple views to the same document,
other programs don't. In practice it might not be a big drawback.


*** DONE figure out what to do with the multiple frames case. 
    CLOSED: [2011-06-27 Mon 12:52]
This should be easier to solve with MVC.
Surprisingly, this just worked!
*** DONE how to propagate changes in views to other views?
    CLOSED: [2011-06-27 Mon 12:53]
I used gtk signals, the implementation for sliders works well!

** TODO canvas support
heresy an interesting comparision of gtk canvases
http://live.gnome.org/ProjectRidley/CanvasOverview
*** goocanvas
goocanvas is a gtk canvas implemented using cairo. investigate.

pros:
- it has a MVC model aproach out of the box which is nice.

http://developer.gnome.org/goocanvas/unstable/goocanvas-model-view-canvas.html

export CFLAGS="`pkg-config --cflags goocanvas` -DHAVE_GOOCANVAS"
export LDFLAGS=`pkg-config --libs goocanvas`
./configure
make

I made a hello goo world xwidget so seems doable.
I wanted to load a SVG which wasnt immediately straightforward, so I
tried clutter. but it turns out the exact same strategy could be used
with goocanvas.

*** clutter
maybe clutter can be used as a canvas? 
pros:
- seems to have a lot of traction atm. many examples
- potentialy fast and cool vector graphics
cons:
- no out of the box MVC support, but seems doable. no worse than the
  other home brew mvc support I have in xwidgets
(media-explorer in an application that employes the MVC pattern)

http://www.openismus.com/documents/clutter_tutorial/0.9/docs/tutorial/html/sec-stage-widget.html

there is also cool stuff like this:
http://gitorious.org/webkit-clutter/webkit-clutter which is an webkit actor for
clutter! hmmmmm.

I want to render svg. aparently:
  librsvg rsvg_handle_render_cairo(h, cr);
  ClutterCairoTexture
  Clutter

export CFLAGS="`pkg-config --cflags clutter-gtk-1.0` -DHAVE_CLUTTER"
export LDFLAGS=`pkg-config --libs clutter-gtk-1.0`
./configure
make

compiles but I get:
Gtk-ERROR **: GTK+ 2.x symbols detected. Using GTK+ 2.x and GTK+ 3 in
the same process is not supported

export CFLAGS="`pkg-config --cflags clutter-gtk-0.10` -DHAVE_CLUTTER"
export LDFLAGS=`pkg-config --libs clutter-gtk-0.10`
./configure
make


** DONE mvc code crashes after a while
   CLOSED: [2011-07-12 Tue 18:52]
seemingly only when compiling with optimizations.
I have no idea why.

Doesn't seem to happen after some code cleanups.
** DONE xwidget-resize-at
   CLOSED: [2011-07-19 Tue 14:28]
reimplement so display spec is not involved
** DONE display spec validation
   CLOSED: [2011-07-19 Tue 14:44]
it is an error to reuse xwidgets in several buffers or in the same
buffer. how do we catch these errors? 
- showing the same xwidget twice in a buffer is no more wrong than
  showing in several emacs windows, just conceptually wrong, so ignore
  this case for now
- xwidgets now store a reference to the buffer they were created in,
  so use that to invalidate xwidget references in oher buffers. but
  thats not really an error either
- xwidgets should now be proper lisp objects so you dont delete them
  you await their garbage collection. so therefore there can never be
  invalid disploy specs

so turned out this got solved by using proper lisp objects for
xwidgets. yay!


** TODO browser xwidget
although embedding a browser is not my primary concern many are
interested in this. some suitable browser component needs to be found
supporting gtk.

*** DONE webkit
    CLOSED: [2011-07-03 Sun 22:13]
there is a webkit gtk port. there is no obvious mvc support.
http://live.gnome.org/WebKitGtk
http://webkitgtk.org/

it might be possible to keep a set of webxits in artificial
synchronisation by recursive deep copy of the DOM from one webkit to
another. This will be error prone at best though. Another way might be
to just use bitmap copy of the "live"instance to the "phantom"
instances. the problem of transfering the live view remains though.

export CFLAGS="`pkg-config --cflags webkit-1.0` -DHAVE_WEBKIT -g"
export LDFLAGS=`pkg-config --libs webkit-1.0`
./configure
make

**** off screen rendering
export CFLAGS="`pkg-config --cflags webkit-1.0` -DHAVE_WEBKIT_OSR -g"
export LDFLAGS=`pkg-config --libs webkit-1.0`
./configure
make

works a little bit  but i get errors like:

(emacs:8362): GLib-GObject-WARNING **: invalid cast from `GdkOffscreenWindow' to `GdkDrawableImplX11'

set a breakpoint in g_log, backtrace seems to indicate
webkitViewportAttributesRecompute is the offender. 

maybe try gtk3 variants?

export CFLAGS="`pkg-config --cflags webkitgtk-3.0 ` -DHAVE_WEBKIT_OSR "
export LDFLAGS=`pkg-config --libs webkitgtk-3.0 `
./configure   --with-x-toolkit=gtk3
make

crash in gtk_window_get_size instead. great.

http://gtkplus-p3.0.sourcearchive.com/documentation/2.91.5-0ubuntu1/testoffscreenwindow_8c-source.html

after many atempts, the basic issue remains. for some reason the
offscreen widget isnt ok when I want to snapshot it, so i simply get
emptiness. the surface is only ok someimes. 

here is a useful debugging snippets:
  // debugging redraw:
  //  - the bg colors always change, so theres no error in signal handling
  //  - i get this error now and then:
  //(emacs:7109): GLib-GObject-WARNING **: invalid cast from `GdkOffscreenWindow' to `GdkDrawableImplX11'
  // seems to happen in webkit actually. see README
  
  if(0){ //redraw debug hack. helped a lot in fact. use the with alpha painter below also
    cairo_set_source_rgb(cr, osr_dbg_color, 1.0, 0.2);
    cairo_rectangle(cr, 0,0, xw->width, xw->height);
    cairo_fill(cr);
    osr_dbg_color+=0.1;
    if(osr_dbg_color>1.0)
      osr_dbg_color=0.0;
    
  }

you need to terminate drawing like this:
  
  //cairo_set_source_surface (cr, src_pixmap, 0,0); 
  //cairo_set_operator (cr, CAIRO_OPERATOR_OVER);

  //cairo_paint_with_alpha (cr, 1.0);
  //cairo_paint(cr);

the snippets change background color on oach redraw. 

**** on-screen rendering to separate window
an alternative might be to open a separate window and snapshot it. the
idea is that whatever oddness webkit does so that offscreen rendering
doesnt work, doesnt happen on-screen. the window could be opened
somewhere not in the way.

*** CANCELLED firefox
    CLOSED: [2011-07-03 Sun 22:13]
http://www-archive.mozilla.org/unix/gtk-embedding.html
seems to be severly bitrotted

heres a newer aproach
http://hg.mozilla.org/incubator/embedding/file/29ac0fe51754/gtk/tests/test.cpp

while webkit clearly has the best traction as an embeddee, the
offscreen rendering issues makes it interesting to see what ff brings
to the table. turns out webkit has as good offscreen support as anyone.


*** TODO text field support
Emacs captures all keyboard events so text field support isn't super
straightforward. 

**** propagate keyboard events
I have some old hacks for this and they are not good.
**** use the DOM model
expose document.activeElement to lisp. This is potentially more
interesting than just forwarding keyboard events.

webkit_web_view_get_dom_document ()

this is hard it seems. an idea might be to hack elisp support for swig
to machine generate the bindings. 
**** DONE inject javascript
     CLOSED: [2011-07-03 Sun 22:50]
webkit_web_view_execute_script ()

this works now:
(xwidget-webkit-execute-script 5 "document.activeElement.value='test'")

so it should be possible to do some interesting stuff.
execute-script does however not return anything at the interface level
so satisfaction is not total:

http://markmail.org/message/4yowmdgras73z3x5

maybe
https://launchpad.net/gnome-seed

or this funny hack:
<jave> im trying to understanh how to interact via javascript to an embedded
       webkit gtk instance  [23:38]
<jave> i use webkit_web_view_execute_script() which is nice but doesnt return
       a value, by design aparently  [23:39]
<jave> any hints?
<lucian> jave: afaik, webkit still doesn't have full gobject bindings  [23:48]
<lucian> jave: you can hack it up by making the JS modify the title, and read
         the title from gtk-side
<jave> lucian: that was a pretty cool idea!


*** webkit_web_view_load_string ()
I would like preview of html in a buffer rather than from uri.



*** TODO simple xwidget-webkit wrapper
so that it could be used for actual browsing :)
I dont want to reinvent too many wheels so i'd like to use existing
emacs facilities here possible. use bindings similar to w3m(or info)

- m-x xwidget-webkit starts a session
- 'g' goes to a url
- use bookmark-jump i suppose. I mostly use org for bookmarks myself
- browse-url support so webkit can be the default browser
- some way of getting around the quirky keyboard interaction since
  xwidgets dont receive keyboard events because I hawe no idea how to
  do that in a sane way

... and one can of course go on bikeshedding forever. lets keep it
simple and extensible, and compatible with other Emacs packages.

the really cool ideas would need Emacs DOM integration, which is not
easy. 

** DONE clipping of controllers
   CLOSED: [2011-07-05 Tue 11:33]

Emacs uses a big GTK window and does its own clipping against Emacs
windows inside this area. So, in order to layout gtk widgets in emacs
windows we must clip thim ourselves. 

The following method worked well for a long time:
- make a gtk widget, say a button, xw
- make a clipping area, of type gtkfixed(many types have been tested)
- put the clip area in the main emacs gtk window
- figure out clip area changes during emacs redisplay

the only weirdness was that one has to tell gtk the clip area has a
window in order to get clipping. This is weird because all gtkwidgets
are windows in a sense and a window is almost by definition also a
clipping area.

Anyway, in GTK3 the   gtk_widget_set_has_window(GTK_WIDGET (
xv->widgetwindow), TRUE); call is ignored. 

The gtkeventbox which is documented to have its own window doesnt work
either.

http://www.lanedo.com/~carlos/gtk3-doc/chap-drawing-model.html

anyway clipping is rather complicated but seems to finally work okay.

*** DONE subclass my own clipping widget
    CLOSED: [2011-07-04 Mon 16:55]
http://www.lanedo.com/~carlos/gtk3-doc/GtkWidget.html#gtk-widget-set-has-window
mentions that it has_window can only be called inside a widget
impementation.

this wasnt really the issue. allocation was the problem
*** DONE try scrolled window
    CLOSED: [2011-07-01 Fri 10:56]
clipping does in fact work with
gtk_scrolled_window_add_with_viewport (xv->widgetwindow, xv->widget);
!!

I get unwanted scrollbars in the widget though.

  gtk_scrolled_window_set_policy      (  xv->widgetwindow,
  GTK_POLICY_NEVER, GTK_POLICY_NEVER); 

stops clipping from working! 


*** DONE try viewport
    CLOSED: [2011-07-01 Fri 10:56]
gtkviewport is used in scrolled window so in order to remove
scrollbars it should be possible to use viewport directly. however, 
viewport ignores size requests. or rather the container does.


*** DONE debug allocation
    CLOSED: [2011-07-04 Mon 16:56]
the container determines how much size to allocate to child widgets.

        GtkAllocation galloc;
        gtk_widget_get_allocation(GTK_WIDGET (xv->widgetwindow), &galloc);
        printf("allocation %d %d , %d %d\n", galloc.x,galloc.y,galloc.width,galloc.height);

after my clipping attemp shows that my size request is ignored! this
might be logical, since the container provided by emacs is a
gtkfixed. gtkfixed might choose to heed the widgets size desires and
allocate the entire widget size. but we want clipping!

since i cant reasonably expect to change the emacs main container, i
can maybe overide the setallocation method in gwfixed, and adjust
allocation to clipping if its an xwidget asking for allocation.

**** DONE subclass gtkfixed
     CLOSED: [2011-07-04 Mon 16:56]
possibly i need to subclass gtkfixed and override

void                gtk_widget_size_allocate            (GtkWidget *widget,
                                                         GtkAllocation *allocation);

http://developer.gnome.org/gobject/stable/howto-gobject.html

turns out emacs already does this for gtk3 according to jan D:
>>For GTK3, Emacs already subclasses GtkFixed, see emacsgtkfixed.[ch].

- widgets may not be underallocated, aparently
http://mail.gnome.org/archives/commits-list/2011-April/msg10950.html

- how to call base class method/chain up
http://developer.gnome.org/gobject/stable/howto-gobject-chainup.html

- the allocation modification could happen in the container or the
  child. it feels more apropiate in the container

it is however unexpectedy inconvenient to modify allocation because
the needed data is private to the base class. to overcome this:

 - run base class method 1st. 
 - then, iterate all children, and modify allocation  for xwidget
   children only. x y will then be set.

JanD pointed out the GTK3 port already has its own subclass, so I
modified that one.

*** DONE clip top
    CLOSED: [2011-07-05 Tue 11:30]
there are four controller edges that potentialy need clipping. I begun
with right and bottom edges. clipping them is just a matter of setting
the right size of the widgetwindow and also ensure it gets the right
allocation from the container.

clipping top (and left) is not equally straightforward. I'm using a
viewport now and scroll it the amount that needs to be clipped.
however, the viewport is sensitive to changes in allocation, which
makes it harder to use the allocation workarounds.

see:
- gtk_widget_set_size_request
- gtkscrolledwindow

I returned to using a simple gtkfixed for the widgetwindow. with
allocation hack and set_has_window it works. Idea prefer not to have
the allocatien hack and it wasnt needed it gtk3 only gtk2. needs
furthi investigation,

** TODO various code cleanups
There are many cleanups necessary before any hope of inclusion in
Emacs trunk. To begin with, the part of the patch that touches other
parts of emacs must be very clean. 
*** TODO use FRAME_GTK_WIDGET (f)
rather than gwfixed.

*** DONE support configure
    CLOSED: [2011-07-12 Tue 18:48]
** DONE translate clicks 
   CLOSED: [2011-07-03 Sun 22:12]
on onscreen webkit peer to offscreen

maybe
http://developer.gnome.org/gdk/stable/gdk-Windows.html#GdkWindow-from-embedder

turned out to be not so hard, captured events, copied them and
forwarded them offscreen!

** TODO investigate gdk_window_redirect_to_drawable
http://developer.gnome.org/gdk/stable/gdk-Windows.html#gdk-offscreen-window-set-embedder
maybe control be used in place of my own copy hacks? to work it must
support a chain of redirects, which seems unlikely. the benefit would
be that I dont have to spend time optimizing redrawing.



** DONE remove xwidget_views when emacs window is deleted
   CLOSED: [2011-07-05 Tue 11:29]
removing xwidget views when an Emacs window closes is not reliable.

- switching buffers in a window seems to hide the corresponding
  xwidget-views properly, but they might as well be deleted.

-  patching delete-window-internal could be used to delete the xwidget-views
this seems to work


** TODO support webkit signals
particularily document-load-finished
http://webkitgtk.org/reference/webkitgtk-webkitwebview.html#WebKitWebView-document-load-finished
** notes from x_draw_xwidget_glyph_string

    BUG it seems this method for some reason is called with bad s->x and s->y sometimes.
    When this happens the xwidget doesnt move on screen as it should.
    This mightbe because of x_scroll_run. Emacs decides to scroll the screen by blitting sometimes.
    then emacs doesnt try to actualy call the paint routines, which means this here code will never
    run so the xwidget wont know it has been moved.

    Solved temporarily by never optimizing in try_window_reusing_current_matrix().

    BUG the phantoming code doesnt work very well when the live xwidget is off screen.
    you will get weirdo display artefacts. Composition ought to solve this, since that means the live window is
    always available in an off-screen buffer. My current attempt at composition doesnt work properly however.

    //allocation debugging. the correct values cant be expected to show upp immediately, but eventually they should get to be ok
    // this is because we dont know when the container gets around to doing layout
    //GtkAllocation galloc;
    //gtk_widget_get_allocation(GTK_WIDGET (xv->widgetwindow), &galloc);
    //printf("allocation %d %d , %d %d\n", galloc.x,galloc.y,galloc.width,galloc.height);


*** old notes about the old live/phantom scheme

   //TODO:
   // 1) always draw live xwidget in slected window
   // (2) if there were no live instances of the xwidget in selected window, also draw it live)
   // 3) if there was a live xwidget previously, now phantom it.

   else
     {
       //ok, we are painting the xwidgets in non-selected window, so draw a phantom
       //printf("draw phantom xwidget at:%d %d\n",x,y);
       //xwidget_composite_draw_phantom (xw, x, y, clipx, clipy); //TODO MVC there will be very few cases of phantoming
     }


   atm this works as follows: only check if xwidgets are displayed in the
   "selected window". if not, hide them or phantom them.

   this means valid cases like xwidgets being displayed only once in
   non-selected windows, does not work well. they should also be visible
   in that case not phantomed.