| Allegro CL version 8.2 Unrevised from 8.1 to 8.2. 8.1 version |
The class of all Common Graphics streams, which include windows,
menu
s, bitmap-stream
s,
printer
streams, and the screen (see screen). These objects are
instances of the Common Lisp stream
class (specifically of the simple-stream
class) because,
like other output streams, these objects are opened and closed, and a
stream of output may be written to them while they are open (and only
then). (An exception is that stream output may not be written to a
menu, but it still is usable only while it is open.)
While conventional streams deal with a one-dimensional sequence of
characters or bytes, most cg-stream
s deal with
two-dimensional graphical output. This output is still ordered in
time though, and therefore can still be thought of as a flowing stream
of graphical output.
In addition to using Common Graphics drawing functions such as
draw-line and copy-to-stream to draw on cg-stream
s, the text
output functions of Common Lisp such as print and format may also be used to draw text to a
cg-stream
.
These functions will draw at the current-position of the stream and
update the current-position to the end of the
text. Text is simply one kind of graphical output that may be sent to
a cg-stream
.
All windows and the screen are always interactive streams (see interactive-stream-p), not because the
user may prompt for stream input in them, but because output to these
streams is often intended to be visible to the user immediately in
interactive user interfaces. Since interactive streams always call
force-output automatically
after each call to text output functions, it should never be necessary
for an application to call force-output or finish-output on a window or the screen. For
other cg-stream
s, all of the Common
Graphics graphical drawing functions will do a force-output just before they do their drawing,
and so it should not be necessary to call force-output or finish-output between drawing Common Lisp text
output and drawing Common Graphics graphical output to the same
cg-stream
in
order to ensure that everything is drawn in the correct order.
The text-edit-pane
(along with its
subclasses such as rich-edit-pane
) is the only cg-stream
class that
can do input. This window is actually a control. It is usually used
only for text input and output, as a file stream might be used, but
arbitrary graphical drawing may also be done to it as well. (Being a
control, graphical output to a text-edit-pane
must be surrounded
by a call to with-device-context.)
A diagram of window and widget classes is shown in Widget and window classes in cgide.htm.
Copyright (c) 1998-2016, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.1 page.
Created 2010.1.21.
| Allegro CL version 8.2 Unrevised from 8.1 to 8.2. 8.1 version |