DRAW-CONTEXT(2) DRAW-CONTEXT(2)
NAME
Context - graphics environment
SYNOPSIS
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;
};
DESCRIPTION
The Context type encapsulates the data types and channels
used by an interactive application, and establishes a con-
text for graphics output and window management. A reference
to the Context is passed as the first argument to an appli-
cation when 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 one
from their parent, typically a shell or window system.
Context interface
The following elements of Context are used by wm:
display The Display adt to which the application is con-
nected; may be nil. See draw-display(2).
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DRAW-CONTEXT(2) DRAW-CONTEXT(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 channel; the tuple contains a
string (eg, an acknowledgement or diagnostic) and a
reference to a Wmcontext value containing channels
by which the application can interact with the win-
dow manager.
Wmcontext interface
The Wmcontext provides a set of channels and file descrip-
tors through which the window manager and application inter-
act. 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
devpointer(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 applica-
tion when the connection closes (eg, if the applica-
tion exits unexpectedly). Connfd is also used to
write requests to the window manager. Convention-
ally 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 rectan-
gle 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 sus-
pend operations on the window), and then the
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DRAW-CONTEXT(2) DRAW-CONTEXT(2)
original image, with its origin set appropriately.
image This is used as described above.
ctxt Initialised with the ctxt value that provided the
initial connection on the wm channel.
SEE ALSO
wm(1), wmlib(2), mux(1), draw-intro(2), ir(2), prefab-
intro(2), tk(2)
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