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 context for graphics output
and window management. A reference to the Context is passed as the
first argument to an application 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 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 con‐
taining a request string (of a format defined by the window man‐
ager) and a private reply channel. It receives a tuple in reply
on that channel; the tuple contains a string (eg, an acknowl‐
edgement or diagnostic) and a reference to a Wmcontext value
containing channels by which the application can interact with
the window manager.
Wmcontext interface
The 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:
kbd A channel of type int that delivers keystrokes from a keyboard.
ptr A channel of type ref Pointer that delivers events from a point‐
ing device such as a mouse. See devpointer(2).
ctl A channel of type string that delivers control messages 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 connec‐
tion control. For instance, a client can store a file descrip‐
tor open on a 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 unex‐
pectedly). 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 exclama‐
tion mark (!) if successful will result in an image being sent
down the 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 opera‐
tions on the window), and then the original image, with its ori‐
gin set appropriately.
image This is used as described above.
ctxt Initialised with the ctxt value that provided the initial con‐
nection on the wm channel.
SEE ALSOwm(1), wmlib(2), mux(1), draw-intro(2), ir(2), prefab-intro(2), tk(2)DRAW-CONTEXT(2)
