= Tk: toplevel, namechan, cmd, pointer, keyboard, imageget, imageput, quote, rect: graphics toolkit     include "draw.m";    include "tk.m";    tk := load Tk Tk->PATH;    Image:    import Draw;        Toplevel: adt    {        display:    ref Draw->Display;        wreq:       chan of string;        image:      ref Image;        ctxt:       ref Draw->Wmcontext;        screenr:    Draw->Rect;    };        toplevel: fn(display: ref Draw->Display, arg: string): ref Toplevel;    namechan: fn(top: ref Toplevel, c: chan of string, n: string): string;    cmd:      fn(top: ref Toplevel, arg: string): string;    pointer:    fn(top: ref Toplevel, p: Draw->Pointer);    keyboard: fn(top: ref Toplevel, key: int);    getimage: fn(top: ref Toplevel, name: string):                 (ref Image, ref Image, string);    putimage: fn(top: ref Toplevel, name: string, i, m: ref Image): string;    rect:     fn(top: ref Toplevel, name: string, flags: int): Draw->Rect;    quote:    fn(s: string): string;    color:    fn(s: string): int; The Tk module provides primitives for  building  user  inter‐faces,  based  on  Ousterhout's Tcl/TK.  The interface to thetoolkit itself is primarily the passing  of  strings  to  andfrom  the elements of the toolkit using the cmd function; seesection 9 of this manual for more information about the  syn‐tax  of those strings.  Tkclient(2) is conventionally used tocreate tk windows that interact correctly with a running win‐dow manager. Toplevel  creates  a  new  window called a Toplevel, which isunder the control of the Tk toolkit, on an existing  display,usually  one  inherited  from the graphics Context (see draw-context(2)).  The Toplevel is  passed  to  cmd  and  namechan(q.v.)   to drive the widgets in the window.  Arg is a stringcontaining creation options (such as -borderwidth 2) that areapplied when creating the toplevel window. Cmd  passes  command strings to the widgets in the Toplevel tand returns the string resulting from their  execution.   Forexample, given a canvas .c in the Toplevel t,    x := int tk->cmd(t, ".c cget -actx");returns the integer x coordinate of the canvas. Bindings can be created in a Toplevel that trigger strings tobe sent on Limbo channels.  Such channels must be declared tothe  Tk module using namechan.  For example, to create a but‐ton that sends the word Ouch when it is pressed:    hitchannel := chan of string;    tk->namechan(t, hitchannel, "channel");    tk->cmd(t,         "button .b.Hit -text Hit -command {send channel Ouch}");    expl := <-hitchannel;     # will see Ouch when button pressed Pointer and keyboard pass mouse and keyboard events to  a  Tkwindow  for  delivery to widgets; they must be called by eachapplication, which usually  receives  them  via  a  Wmcontextstructure (see draw-context(2)) obtained from the window man‐ager, often via tkclient(2). Putimage passes an image and a mask into Tk.  If name is  thename  of a Tk widget, it must be either a panel(9) widget, ora top level widget (ie, ``.'')  ``.'')  or a menu widget,  inwhich  case the associated image or window image is set to i.(m is ignored for menu and  top-level  widgets.)   Otherwise,name  must  be the name of an existing image(9) which has itsimage and mask set to copies of i and m respectively. Initially, a Tk toplevel has no image to draw  on.   Tk  useswreq  to  request new images of an external authority, and toinform said authority when the images are to be deleted.  Therequests  are  formatted as per quoted in string(2), and holdone of the following: !reshape name reqid minx miny maxx maxy       A new image for name is requested (name is either  the       toplevel widget or a menu).  The desired rectangle for       the new image is given by [minx miny maxx  maxy],  and       the application should respond by creating a new image       and using putimage to pass it to Tk.  Reqid is used by       Tk  to  filter  out responses to out-of-date requests;       when responding to a reshape request, the name  passed       to  putimage  should  have a space and reqid appended.       Tkclient(2) usually deals with the details of this. delete name       The image name has been deleted. This is generated for       menu(9) widgets when they are unmapped. raise name       Tk widget name should be raised above other windows on       the same screen. lower name       Tk widget name should be lowered beneath other windows       on the same screen. Wreq  may  be set to nil if an application is not prepared toread requests sent on this channel. Rect returns the bounding rectangle of widget  name  in  top.Flags determines the form of rectangle returned.  If flags iszero, the actual rectangle of name in screen coordinates, notincluding its border, is returned. The bitmask flags that canchange this are: Border Include the widget's border. Required       Return the rectangle required by  the  widget,  rather       than the rectangle that has been actually allocated to       it. Local  Return the rectangle in coordinates  relative  to  the       logical origin of the actual top level image. Quote returns a string that is the same as its arguments, butenclosed in curly  braces  and  with  internal  curly  bracesescaped.  This can be used to make an arbitrary string into aword suitable as an argument to a Tk function. Color returns a colour in 32-bit RGBA format corresponding tothe tk colour name s.  (see types(9) for details). Screenr  gives  the  rectangle  of  the screen containing thetoplevel window.  Tk has no a priori way of knowing what thisis;  it  is  initially  set  to  the rectangle of the displayimage, and may be set by the application if it  knows  better(e.g. from the wmrect file served by wm(1)). == source/libinterp/tk.c/libtk/*.c == see ALSOintro(9),  image(9),  panel(9), tkcmd(1), sh-tk(1), draw-con‐text(2), tkclient(2), wmlib(2)`An Overview of Limbo/Tk', this manual, Volume 2.