Octave/backend interface proposal

[Michael Goffioul]

Hi,

Following a chat I had with Shai, we though we would need at some
point in time some kind of interaction between octave and any
graphics backend (to exchange some information). After some
discussions, we agreed on a scheme, whose skeleton would
be something like in the attached files.

The idea is to define a graphics_backend interface (that the
actual backend would implement) and attach to a figure the
backend to which it belongs, which serves as an entry point
for octave/backend interaction. This scheme should allow
multiple backends running at the same time.

Example of possible interaction are:
- closing a figure window
- getting font metric information
- getting drawing canvas size (useful to deal with normalized
units)
- other things we didn't think about yet

For the moment, only a gnuplot backend is defined and will
be used as default.

If you're OK with the concept (and the implementation), please
commit.

Michael.

graphics-backend.h
Description: Text document

graphics-backend.cc
Description: Text document

backend.diff
Description: Text document