Here is the method I successfully use:
I have a class called daViewMap which is derived from Gtk::DrawingArea
I use a Cairo::ImageSurface to import a 2-D array into an useful image form
for Cairo.
class daViewMap : public Gtk::DrawingArea
{
public:
Cairo::RefPtr<Cairo::ImageSurface> viewSurface;
Cairo::RefPtr<Cairo::Context> myCr;
};
daViewMap::daViewMap() :
{
viewSurface = Cairo::ImageSurface::create(&viewMap[0][0],
Cairo::FORMAT_A8, VIEW_MAP_X, VIEW_MAP_Y, VIEW_MAP_X );
myCr = Cairo::Context::create(viewSurface);
}
I perform all the cairo-based drawing using the context daViewMap->myCr
and then extract the image via a button callback:
void exportImage(std::string filename)
{
Glib::RefPtr<Gdk::Window> win2 = daViewMap->get_window();
if (win2)
{
Glib::RefPtr<Gdk::Drawable> dra2 =
Glib::RefPtr<Gdk::Window>::cast_dynamic(win2);
Glib::RefPtr<Gdk::Pixbuf> img2 = Gdk::Pixbuf::create(dra2 ,0 ,0
,daViewMap->get_allocation().get_width(),
daViewMap->get_allocation().get_height());
img2->save(filename,Glib::ustring("png"));
}
}
Note the use of a Pixbuf to extract the image from the drawing area's space,
and then we use that to save it out to a file.
Hope that makes sense...
Chris Wilson
On Mon, Aug 11, 2008 at 5:48 PM, John Hobbs <[EMAIL PROTECTED]> wrote:
> Hello, I apologize if this is off-topic as it deals a lot with Cairo,
> I feel it is a borderline thing. Please feel free to send me packing
> to somewhere else if I'm wrong on that point :-)
>
> I'm trying to load an image into a DrawingArea, then put lines on it
> with Cairo and get that back out. Is this possible or do I need to go
> figure out something with GC and Drawable?
>
> Here's the guts of the procedure so far, sorry it's big but I don't
> know how to trim it down and keep it understandable.
>
> ---------------------------------------------
> class ExampleWindow : public Gtk::Window {
>
> public:
> ExampleWindow (std::string path) {
> imagePB = Gdk::Pixbuf::create_from_file(path);
>
>
> drawOnMe.signal_expose_event().connect(sigc::mem_fun(*this,&ExampleWindow::on_da_expose_event));
> add(drawOnMe);
> show_all();
> }
>
> private:
> Gtk::DrawingArea drawOnMe;
> Glib::RefPtr<Gdk::Pixbuf> imagePB;
>
> bool on_da_expose_event (GdkEventExpose * event) {
> std::cout << "Expose Event" << std::endl;
> Glib::RefPtr<Gdk::Window> window =
> drawOnMe.get_window();
> Cairo::RefPtr<Cairo::Context> context =
> window->create_cairo_context();
> Cairo::RefPtr<Cairo::ImageSurface> image_surface =
> Cairo::ImageSurface::create (Cairo::FORMAT_RGB24,
> imagePB->get_width(), imagePB->get_height());
> Cairo::RefPtr<Cairo::Context> image_context =
> Cairo::Context::create(image_surface);
>
> Gdk::Cairo::set_source_pixbuf (image_context,
> imagePB, 0.0, 0.0);
> image_context->paint();
>
> context->set_source(image_surface, 0.0, 0.0);
> context->paint();
>
> context->set_line_width(5.0);
> context->set_source_rgb(0.8, 0.0, 0.0);
> context->move_to(10,20);
> context->line_to(100, 200);
> context->stroke();
>
> return false;
> }
> };
> ---------------------------------------------
>
> I tried getting a surface from that context after the stroke() call
> and then a write to PNG:
>
> Cairo::RefPtr<Cairo::Surface> sfc = context->get_target();
> sfc->write_to_png("please_work.png");
>
> That just crashed on an expose event and I didn't bother to debug. I
> have the feeling I've gone wrong in my understanding of Cairo.
>
> So I guess what it boils down to is I'm curious if there is an easier
> path by using something in Gtkmm (which I chased my tail for a long
> time trying to find something) or if there is a way to get that drawn
> data back out of there.
>
> Thanks for any and all help :-)
>
> - John Hobbs
>
> [EMAIL PROTECTED]
> _______________________________________________
> gtkmm-list mailing list
> [email protected]
> http://mail.gnome.org/mailman/listinfo/gtkmm-list
>
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