drawing scaled images with cairomm

[Christopher Harvey <chris basementcode com>]

I've got the following code (pasted below) that stores a
Cairo::RefPtr<Cairo::ImageSurface> created from a Gdk::PixBuf. When I
draw this image it is about 30x30, and I want to be able to scale it up.
I don't care too much about the filtering, but it would be cool if
cariomm could do it for me rather than allocating tons of memory and
scaling myself just to display a larger version of a 30x30 image. Again,
I don't care about the filtering algorithm, I just can't figure it out
in general from the docs....
Thanks.



The term PDF here means probability distribution function, not portable
document format.

Cairo::RefPtr<Cairo::ImageSurface> currentImage;
Window *window = NULL;

bool updatePDF(double dt) {
  const unsigned int w(g_pf->getWidth());
  const unsigned int h(g_pf->getHeight());

  std::vector<unsigned char> data(w*h*3);
  for(unsigned int i = 0;i<data.size();i+=3) {
    data[i] = 255;
    data[i+1] = 0;
    data[i+2] = 0;
  }

  Glib::RefPtr<Gdk::Pixbuf> pb;
  pb = Gdk::Pixbuf::create_from_data(&data[0], Gdk::COLORSPACE_RGB,
				     false, 8, w, h, w*3);


  currentImage = Cairo::ImageSurface::create(Cairo::FORMAT_RGB24,
					     pb->get_width(), pb->get_height());

  Cairo::RefPtr<Cairo::Context> image_context_ptr =
Cairo::Context::create(currentImage);

  // Draw the image on the new Context
  Gdk::Cairo::set_source_pixbuf(image_context_ptr, pb, 0.0, 0.0);
  image_context_ptr->paint();

  window->queue_draw();

  return true;
}

bool drawPDF(GdkEventExpose *e, DrawingArea *area) {

  // This is where we draw on the window
  Glib::RefPtr<Gdk::Window> window = area->get_window();
  if(window) {
    Gtk::Allocation allocation = area->get_allocation();
    int width = allocation.get_width();
    int height = allocation.get_height();
    Cairo::RefPtr<Cairo::Context> cr = window->create_cairo_context();

    if(e) {
      // clip to the area indicated by the expose event so that we only
      // redraw the portion of the window that needs to be redrawn
      cr->rectangle(e->area.x, e->area.y,
		    e->area.width, e->area.height);
      cr->clip();
    }

    double line_width = 0.05;

    if(currentImage)
      cr->set_source(currentImage, 0.0, 0.0);
    else
      cr->set_source_rgb(0.0, 0.0, 1.0);
    cr->rectangle(0,0,width,height);
    cr->fill();
  }

  return true;
}