= Context: graphics environment     include "draw.m";    draw := load Draw Draw->PATH;     Context: adt    {       display: ref Display;      # frame buffer on which windows reside       wm:      chan of (string,                   chan of (string, ref Wmcontext)); # wmgr connection    };     # connection to window manager for one or more windows (as Images)    Wmcontext: adt    {       kbd:     chan of int;         # incoming characters from keyboard       ptr:     chan of ref Pointer; # incoming stream of mouse positions       ctl:     chan of string;      # commands from wm to application       wctl:    chan of string;      # commands from application to wm       images:  chan of ref Image;   # exchange of images       connfd:  ref Sys->FD;         # connection control       ctxt:    ref Draw->Context;    }; The  Context  type  encapsulates  the data types and channelsused by an interactive application, and establishes a contextfor  graphics  output  and window management.  A reference tothe Context is passed as the first argument to an applicationwhen it begins execution: include "draw.m" Command: module{     init: fn(nil: ref Draw->Context; nil: list of string);}; Most  programs do not create Contexts but instead inherit onefrom their parent, typically a shell or window system.    Context interfaceThe following elements of Context are used by wm: display       The Display adt to which the application is connected;       may be nil.  See draw-display(2). wm     A  shared  channel through which a private channel can       be set up with a window manager.  A client application       sends a tuple containing a request string (of a format       defined by the window manager)  and  a  private  reply       channel.   It  receives a tuple in reply on that chan‐       nel; the tuple contains a string (eg, an  acknowledge‐       ment  or  diagnostic)  and  a reference to a Wmcontext       value containing channels by which the application can       interact with the window manager.    Wmcontext interfaceThe Wmcontext provides a set of channels and file descriptorsthrough which the window manager  and  application  interact.The elements of the adt are used as follows: kbd    A  channel of type int that delivers keystrokes from a       keyboard. ptr    A channel of type ref  Pointer  that  delivers  events       from  a  pointing  device  such  as a mouse.  See dev‐       pointer(2). ctl    A channel of type string that  delivers  control  mes‐       sages from the window manager to the application. wctl   A channel of type string, which if initialised is used       by the application to send  control  messages  to  the       window  manager.   It is not used by the current wm(1)       or tkclient(2). images A channel of type ref Image  that  allows  the  window       manager  and  application to exchange images (eg, when       resizing, or to supply a cursor image). connfd A file descriptor that can be  used  to  provide  per-       client connection control.  For instance, a client can       store a file descriptor  open  on  a  sys-file2chan(2)       provided by the window manager, and the window manager       will shut down input to the application when the  con‐       nection closes (eg, if the application exits unexpect‐       edly).  Connfd is also used to write requests  to  the       window manager.  Conventionally a request is a list of       words formatted as by quoted in string(2).  A  request       starting  with  an exclamation mark (!)  if successful       will result in an image  being  sent  down  the  image       channel; the rectangle of the image indicates the rec‐       tangle that has been allocated on the screen. If  only       the  origin  is to be changed by the window manager, a       nil image is sent  first  (giving  the  application  a       chance  to suspend operations on the window), and then       the original image, with its origin set appropriately. image  This is used as described above. ctxt   Initialised with the ctxt value that provided the ini‐       tial connection on the wm channel. == see ALSOwm(1),   wmlib(2),   mux(1),  draw-intro(2),  ir(2),  prefab-intro(2), tk(2)