ref: e2e50a8e5a74452672f9418bcdfe4de10f600ed0
dir: /man/2/draw-context/
.TH DRAW-CONTEXT 2
.SH NAME
Context \-
graphics environment
.SH SYNOPSIS
.EX
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;
};
.EE
.SH DESCRIPTION
The
.B Context
type encapsulates the data types and channels used by an interactive application,
and establishes a context for graphics output and window management.
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
.SS Context interface
.PP
The following elements of
.B Context
are used by
.IR wm :
.TF display
.PD
.TP
.B display
The
.B Display
adt to which the application is connected; may be
.BR nil .
See
.IR draw-display (2).
.TP
.B 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 channel; the tuple contains
a string (eg, an acknowledgement or diagnostic) and a reference to
a
.B Wmcontext
value containing channels by which the application can interact with the
window manager.
.SS Wmcontext interface
The
.B Wmcontext
provides a set of channels and file descriptors
through which the window manager and application interact.
The elements of the adt are used as follows:
.PP
.TF connfd
.PD
.TP
.B kbd
A channel of type
.B int
that delivers keystrokes from a keyboard.
.TP
.B ptr
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 ctl
A channel of type
.B string
that delivers control messages from the
window manager to the application.
.TP
.B wctl
A channel of type
.BR string ,
which if initialised is
used by the application to send control messages to the window manager.
It is not used by the current
.IR wm (1)
or
.IR tkclient (2).
.TP
.B images
A channel of type
.B ref
.B Image
that allows the window manager and application to exchange images
(eg, when resizing, or to supply a cursor image).
.TP
.B 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
.IR sys-file2chan (2)
provided by the window manager, and the window manager will shut down
input to the application when the connection closes (eg, if the application
exits unexpectedly).
.B Connfd
is also used to write requests to the window manager.
Conventionally a request is a list of words formatted as
by
.B quoted
in
.IR string (2).
A request starting with an exclamation mark
.BR "" ( ! )
if successful will result in an image being sent down the
.B image
channel; the rectangle of the image indicates the rectangle
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.
.TP
.B image
This is used as described above.
.TP
.B ctxt
Initialised with the
.B ctxt
value that provided the initial connection on the
.B wm
channel.
.RE
.SH SEE ALSO
.IR wm (1),
.IR wmlib (2),
.IR mux (1),
.IR draw-intro (2),
.IR ir (2),
.IR prefab-intro (2),
.IR tk (2)