Re: embedding gtk widgets in a buffer

[Richard M Stallman]

    - callback interface for the widgets. It would be nice with some ideas
    how to do this. For instance:
      - button pressed handler

The natural way is for this to generate events, and when those events
reach the main loop, they will do whatever it is.

      - when a xembed widget is ready, a callback to start an external
      program in the widget would be nice, now it has to be done manually on
      the cmd line

This callback does not need to be visible from Lisp.
When you create the widget, you specify the command and args
for the command to start the program.  In the C code,
Emacs can handle the callback by starting it.

    - 2 windows showing the same buffer doesnt quite work and is probably tricky

It would be a pain in the neck to have buffers that are not allowed to
appear in more than one window, but this may be necessary for the
xembed case.

Buttons in the buffer ought to be able to work on more than one Emacs
window.

The only way I can think of to make the xembed widgets work in more
than one Emacs window is if you can tell the other program to display
in a pixmap, and then Emacs redisplay would copy that pixmap to the
screen.