On Drawing a Red Line

[Derrick Williams <adw derrickwilliams com>]

 Hello!

 I have just started to learn how to use gtk--, and I have run into
a small puzzle, and it is my hope that the finest human beings on
the planet, all of which read this mailing list, may shine some
illumination on the problem I am experiencing.

 As a test, I wrote a little program which draws a line in a window.
If I stick with the black or white graphics context, it works just
fine. The problem is that, because of weak moral character and
unsolvenly upbringing, I would like to draw the same line in color.
In my case, a red line.

 Here is the class I wrote, called 'RedLine', which is the result of
my poor deductive skills and slow comprehension, and questionable 
programming skills. As you may see, there is probably something I am
doing terribly wrong. I would be interested if I'm taking the wrong
approach in drawing my line, or of any boneheaded code I am writing.

 Here, I attempt to allocate a new color (red), and set the 'fg'
(foreground) color to red, and draw the line. I do not get a red
line, just the black background. You will note that if you uncomment
the line where I reference the 'white_gc', the program works and I
see the white line.

---------------------------- RedLine: ----------------------------------

#include <gtk--.h>
#include <gdk--.h>
#include <gtk/gtk.h>

class RedLine : public Gtk_Window{

public:

  Gdk_Pixmap      pixmap;
  Gdk_GC          gc;

  configure_event_impl (GdkEventConfigure *){

   if(pixmap){
      pixmap.free();
    }

   pixmap.create(get_window(),500,500);
   draw_a_line();
   return TRUE;
 }

 draw_a_line(){

    GdkColor     red={0,0x555,0,0};
    Gdk_Color    new_color(&red);
    Gdk_Colormap sysmap;

    sysmap=Gdk_Colormap::get_system();
    sysmap.alloc(new_color);

    gc = get_style()->gtkobj()->black_gc;
    pixmap.draw_rectangle(gc,TRUE,0,0,500,500);

    get_style()->set_fg(GTK_STATE_NORMAL,red);         
    gc = get_style()->gtkobj()->fg_gc[GTK_STATE_NORMAL];

//    If the next line is uncommented, a white line is drawn
//    gc = get_style()->gtkobj()->white_gc;

    pixmap.draw_line(gc,10,100,180,100);

    get_window().draw_pixmap(gc,pixmap,0,0,0,0,500,500);
 }


 expose_event_impl(GdkEventExpose *event){

    gc = get_style()->gtkobj()->fg_gc[GTK_WIDGET_STATE(GTK_WIDGET(gtkobj()))];
    get_window().draw_pixmap(gc,pixmap,
                       event->area.x, event->area.y,
                       event->area.x, event->area.y,
                       event->area.width, event->area.height);
    return FALSE;
}


  RedLine(){
     //set the events to listen for
     set_events(GDK_EXPOSURE_MASK);
  }
};


int main( int argc, char **argv )
{
   Gtk_Main m( &argc, &argv ); 
   RedLine w; 
   w.show(); 
   m.run(); 
   return 0;
}

-----------------------------END--------------------------------------------

The above is compiled with:


gcc `gnome-config gnomemm --cflags` redline.C `gnome-config gnomemm --libs` -o redline 


No error messages or warnings appear.

I am using RedHat 6.1, with the stock GDK that came with it. I am using
gtk-- 1.03, and there are no modifications I made to any of the libraries.

 Any help or pointers to references would be much appreciated.

 I remain,

 Derrick Williams