DRAW-SCREEN(2) DRAW-SCREEN(2)
NAME
Screen - windows and subwindows on a display
SYNOPSIS
include "draw.m";
draw := load Draw Draw->PATH;
Screen: adt
{
id: int;
image: ref Image;
fill: ref Image;
display: ref Display;
allocate: fn(image, fill: ref Image, public: int): ref Screen;
newwindow: fn(screen: self ref Screen, r: Rect,
backing:int, rgba: int): ref Image;
top: fn(screen: self ref Screen, wins: array of ref Image);
};
DESCRIPTION
A Screen is the data structure representing a set of windows
visible on a particular Image such as the display or a par-
ent window.
id When a Screen object is allocated (see allocate
below), the system assigns it a unique integer,
id. It may be declared ``public'' and accessible
to arbitrary processes and machines with access to
the screen's Display. The id value may be used as
an argument to Display.publicscreen; see draw-
display(2).
fill When windows are deleted from a screen, the system
uses the fill image to repaint the screen's base
image.
image The image upon which the windows appear.
display The display upon which the screen resides.
allocate(image, fill, public)
Allocate makes a new Screen object. The image
argument provides the base image on which the win-
dows will be made. The fill argument provides the
Screen.fill image. Allocate does not affect the
contents of image; it may be necessary after allo-
cation to paint the base image with fill.
Using a non-zero public argument allocates a
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DRAW-SCREEN(2) DRAW-SCREEN(2)
public screen; zero requests a private screen.
Public screens may be attached by any process on
any machine with access to the Display upon which
the screen is allocated, enabling remote processes
to create windows on the screen. Knowing only the
id field of the original Screen, the remote pro-
cess can call the Display.publicscreen function to
acquire a handle to the screen. The image and
fill fields of a Screen obtained this way are nil,
but they are not needed for ordinary window man-
agement.
screen.newwindow(r, backing, rgba)
Allocates a window on the display at the specified
rectangle with the background colour rgba,
expressed in 32-bit RGBA format; the return value
is an Image that may be used like any other. The
backing parameter can be Draw->Refbackup, which
provides backing store to store obscured parts of
the window when necessary, and is used by the win-
dow manager and its clients; or Draw->Refnone,
wihch provides no refresh, and is used for windows
that are transient, or are already protected by
backing store.
screen.top(wins)
Top organizes a group of windows on a screen.
Given wins, an array of window images, it places
the wins[0] element at the top, wins[1] behind
that, and so on, with the last element of wins in
front of the all the windows on the screen not in
wins. Images in the array must be on the specified
screen (nil elements are ignored).
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