Re: exposing cairo context from gnuplot

[Ethan M. <merritt@u.washington.edu>]

On Wednesday 09 September 2009, Allin Cottrell wrote:
> 
> On Wed, 9 Sep 2009, Richard Henwood wrote:
> 
> > On Tue, 2009-09-08 at 09:27 -0700, Ethan Merritt wrote:
> > > On Tuesday 08 September 2009 01:44:25 Richard Henwood wrote:
> > > > On Mon, 2009-09-07 at 17:49 -0400, Allin Cottrell wrote:
> > > > >
> > > > > I think what Richard was asking is whether the "cairo drawing
> > > > > context" struct, or "cairo_t", that is used internally by gnuplot
> > > > > could somehow be exposed programmatically...
> > > >
> > > > This is indeed what I am curious about...
> 
> > > [...] This mode of operation is already supported by the qt,
> > > tkcanvas, and x11 terminal drivers.  You initialize the
> > > context, invoke gnuplot, and tell it to draw into your
> > > existing context rather than creating a new one.  Of course
> > > the details are different in each case.
> >
> > Ah! This is good news. So presumably if a 'cairo' terminal driver
> > existed, this would provide me a way to get nice gnuplot plots into my
> > GTK/cairo application?
> 
> In the meantime a good option, I find, is to get gnuplot to create
> a PNG file (e.g. using the pngcairo terminal), then load that file
> into your GTK window using gdk_pixbuf_new_from_file() or perhaps
> cairo_image_surface_create_from_png().  Of course, you don't
> get a vector graphic that way.
> 
> I'm not quite sure how a "cairo term" would work.  You couldn't
> actually pass a cairo drawing context to gnuplot, could you?

I'm not a gtk programmer, but there's always Google...
which leads me to the plplot project on SourceForge. It seems that
plplot is somewhat similar to gnuplot in intent, but the relevant point
is that they recently added an external cairo terminal driver "extcairo"
that so far as I can tell from the description does exactly what you want.
If it works for them, I don't see why it wouldn't work for us.
Anyonw have time to check out the code and report back on how the
information to open the context is passed?

	Ethan

> With the x11 term, for example, you can say "window <XID>", passing the
> X11 ID of the window you want to draw into, in string form. I
> don't offhand see what a cairo counterpart would look like.
 
> Here's something I haven't tried, but that might be nice. Since
> gnuplot already does SVG, one could get gnuplot to write an SVG
> file, create a cairo context using gdk, then call librsvg to read
> the SVG file into your cairo context.  This would not require any
> modifications to gnuplot.
> 
> Allin Cottrell
>