.TH DRAW-CONTEXT 2
.SH NAME
Context \-
graphics environment
.SH SYNOPSIS
.EX
include "draw.m";
draw := load Draw Draw->PATH;

Context: adt
{
    screen:  ref Screen;
    display: ref Display;
    cir:     chan of int;
    ckbd:    chan of int;
    cptr:    chan of ref Pointer;
    ctoappl: chan of int;
    ctomux:  chan of int;
};
.EE
.SH DESCRIPTION
The
.B Context
type encapsulates the data types and channels used by an interactive application.
A reference to the
.B Context
is passed as the first argument to an application when it begins execution:
.PP
.EX
include "draw.m"

Command: module
{
	init: fn(nil: ref Draw->Context; nil: list of string);
};
.EE
.PP
Most programs do not create
.B Contexts
but instead inherit one from their parent, typically a shell or window system.
.PP
The
.IR wm (1)
and
.IR mux (1)
environments use
.B Context
differently as regards keyboard and pointer (mouse) I/O.
.I Mux
applications are given a set of channels in their
.B Context
structure.
.I Wm
applications provide keyboard and mouse input encoded as Tk events
on a channel named via
.B Tk->namechan
in
.IR tk (2),
and the channels in the
.B Context
are unused,
and
.BR nil .
.SS Common interface
The following elements of
.B Context
are used by both
.I wm
and
.IR mux :
.TF display
.PD
.TP
.B screen
The
.B Screen
adt to which the application is connected; may be
.BR nil .
See
.IR draw-screen (2).
.TP
.B display
The
.B Display
adt to which the application is connected; may be
.BR nil .
See
.IR draw-display (2).
.SS Mux-specific interface
As mentioned above,
.IR mux (1)
primes an application's argument
.B Context
with channels through which
.I mux
and the application interact.
The channels are used as follows:
.PP
.TF ctoappl
.PD
.TP
.B cir
A channel of type
.B int
that delivers events from an infrared remote control device,
if one is present.
See the discussion below and
.IR ir (2)
for more information.
.TP
.B ckbd
A channel of type
.B int
that delivers keystrokes from a keyboard.
.TP
.B cptr
A channel of type
.B ref
.B Pointer
that delivers events from a pointing device such as a mouse.
See
.IR devpointer (2).
.TP
.B ctoappl
A channel of type
.B int
that delivers control messages from the
.IR mux (1)
application multiplexer.
One message is defined:
.RS
.TF MAtop
.TP
.B MAtop
Requests an application to make its set of windows fully visible.
.RE
.TF ctoappl
.PD
.TP
.B ctomux
A channel of type
.B int
used by the application to send messages to
.IR mux (1)
regarding the application's use of system devices.
The defined messages are:
.RS
.TF AMstartkbd
.PD
.TP
.B AMstartir
The application is ready to accept
.IR ir (2)
data on the
.B cir
channel.
.TP
.B AMstartkbd
The application is ready to accept
keyboard data on the
.B ckbd
channel.
.TP
.B AMnewpin
The application needs a PIN.
.TP
.B AMstartptr
The application is ready to accept
.B Pointer
data on the
.B cptr
channel.
.TP
.B AMexit
An application should send this message before it exits, to allow
.I mux
to recover resources.
.RE
.SH SEE ALSO
.IR wm (1),
.IR mux (1),
.IR draw-intro (2),
.IR ir (2),
.IR prefab-intro (2),
.IR tk (2)