[gtkmm] Gdk::Color/Gdk::GC question

[Carl Nygard <cjnygard fast net>]

Can someone tell me why GC::set_rgb_fg_color does not work?  I'm using
the radar.cc example from the .rpm install, here's the code I modified: 
(setting NOTRGB=1 works fine, otherwise black screen)

PPI::PPI()
{
  // get_window() would return 0 because the Gdk::Window has not yet been realized
  // So we can only allocate the colors here - the rest will happen in on_realize().
  Glib::RefPtr<Gdk::Screen> screen = 
      Gdk::Visual::get_best(Gdk::VISUAL_TRUE_COLOR)->get_screen();

//   Glib::RefPtr<Gdk::Colormap> colormap = get_default_colormap();
  Glib::RefPtr<Gdk::Colormap> colormap = screen->get_rgb_colormap();


  blue_ = Gdk::Color("blue");
  red_ = Gdk::Color("red");

  // ....
}

void PPI::on_realize()
{
  // We need to call the base on_realize()
  Gtk::DrawingArea::on_realize();

  // Now we can allocate any additional resources we need
  Glib::RefPtr<Gdk::Window> window = get_window();

  gc_ = Gdk::GC::create(window);

  window->set_background(black_);
  window->clear();

  //  Make sure the same colormap is set in the gc_
  Glib::RefPtr<Gdk::Screen> screen = 
      Gdk::Visual::get_best(Gdk::VISUAL_TRUE_COLOR)->get_screen();
  gc_->set_colormap(screen->get_rgb_colormap());

//   gc_->set_foreground(green_);
}


bool PPI::on_expose_event(GdkEventExpose*)
{
  // we need a ref to the gdkmm window
  Glib::RefPtr<Gdk::Window> window = get_window();

  // window geometry: x, y, width, height, depth
  int winx, winy, winw, winh, wind;
  window->get_geometry(winx, winy, winw, winh, wind);

  window->clear();

  // 4 white points
#if NOTRGB
  gc_->set_foreground(white_);
#else
  {
      Gdk::Color c;
      c.set_rgb(255, 255, 255);
      gc_->set_rgb_fg_color(c);
  }
#endif
  window->draw_point(gc_, 5, 5);
  window->draw_point(gc_, 5, winh-5);
  window->draw_point(gc_, winw-5, winh-5);
  window->draw_point(gc_, winw-5, 5);

  // a thick solid grey line
#if NOTRGB
  gc_->set_foreground(grey_);
#else
  {
      Gdk::Color c;
      c.set_rgb(128, 128, 128);
      gc_->set_rgb_fg_color(c);
  }
#endif
  gc_->set_line_attributes(/*line_width*/7, /*LineStyle*/Gdk::LINE_SOLID,/*CapStyle*/Gdk::CAP_NOT_LAST,/*JoinStyle*/Gdk::JOIN_MITER);
  // LineStyle: LINE_SOLID, LINE_ON_OFF_DASH, LINE_DOUBLE_DASH
  // CapStyle: CAP_NOT_LAST, CAP_BUTT, CAP_ROUND, CAP_PROJECTING
  // JoinStyle: JOIN_MITER, JOIN_ROUND, JOIN_BEVEL
  window->draw_line(gc_, 10, 10, winw-10, winh-10);
  
 // ...
}