DRAW-CONTEXT(2)

NAME

Context − graphics environment

SYNOPSIS

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;
};

DESCRIPTION

The Context type encapsulates the data types and channels used by an interactive application. 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.

The wm(1) and mux(1) environments use Context differently as regards keyboard and pointer (mouse) I/O. Mux applications are given a set of channels in their Context structure. Wm applications provide keyboard and mouse input encoded as Tk events on a channel named via Tk->namechan in tk(2), and the channels in the Context are unused, and nil.

Common interface

The following elements of Context are used by both wm and mux:

screen The Screen adt to which the application is connected; may be nil. See draw-screen(2).

display The Display adt to which the application is connected; may be nil. See draw-display(2).

Mux-specific interface

As mentioned above, mux(1) primes an application’s argument Context with channels through which mux and the application interact. The channels are used as follows:

cir A channel of type int that delivers events from an infrared remote control device, if one is present. See the discussion below and ir(2) for more information.

ckbd A channel of type int that delivers keystrokes from a keyboard.

cptr A channel of type ref Pointer that delivers events from a pointing device such as a mouse. See devpointer(2).

ctoappl A channel of type int that delivers control messages from the mux(1) application multiplexer. One message is defined:

MAtop Requests an application to make its set of windows fully visible.

ctomux A channel of type int used by the application to send messages to mux(1) regarding the application’s use of system devices. The defined messages are:

AMstartir The application is ready to accept ir(2) data on the cir channel.

AMstartkbd The application is ready to accept keyboard data on the ckbd channel.

AMnewpin The application needs a PIN.

AMstartptr The application is ready to accept Pointer data on the cptr channel.

AMexit An application should send this message before it exits, to allow mux to recover resources.

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