Re: exposing cairo context from gnuplot

[Allin C. <cot...@wf...>]

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? 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