[gtkada] Line width : how to ?

[yoann toussaint]

hello,
I would like to draw a line width a specific width (to make a draw brush 
function)
I use the gtk-extra-plot package
and I try :

    L:Gtk_Plot_Line;
    Point :Gtk_Plot;
   begin
      Gtk_New(Point,pixmap);
      Set_Line_Width(L,3.0);

Draw_Line(Point,L,Gdouble(X),gdouble(Y),gdouble(X),gdouble(Y));

but I didn't found a function to instanciate the line like 
gtk_new(l,pixmap) ?
so a storage error is raised :
raised STORAGE_ERROR : stack overflow (or erroneous memory access

how to use it ?
why there is a plot parameter in the function :

*procedure* Draw_Line            
  (Plot               : *access* Gtk_Plot_Record;
   Line               : *      * Gtk_Plot_Line;
   X1, Y1, X2, Y2     : *      * Gdouble);

this function draw a line from x1,y1 to x2,y2 ? why does it need a plot ?

thanks,
yoann