Page 178	Table of Contents	Index	Page 180
	Chapters
	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 A, B, C, D, E

Chapter 21

Incremental Redisplay

21.1 Overview of Incremental Redisplay

CLIM's incremental redisplay facility to allows the programmer to change the output in an
output history (and hence, on the screen or other output device) in an incremental fashion. It
allows the programmer to redisplay individual pieces of the existing output differently, under
program control.

It is "incremental" in the sense that CLIM will try to minimize the changes to the existing
output on a display device when displaying new output.

There are two different ways to do incremental redisplay.

The first is to call redisplay on an output record. This essentially tells the system to recompute
the output of that output record over from scratch. It compares the new results with the existing
output and tries to do minimal redisplay. The updating-output form allows the programmer
to assist CLIM by informing it that entire branches of the output history are known not to have
changed. updating-output also allows the programmer to communicate the fact that a piece of
the output record hierarchy has moved, either by having an output record change its parent, or
by having an output record change its position.

The second way to do incremental redisplay is to manually do the updates to the output history,
and then call note-output-record-child-changed on an output record. This causes CLIM to
propagate the changes up the output record tree and allows parent output records to readjust
themselves to account for the changes.

Each style is appropriate under different circumstances. redisplay is often easier to use, es-
pecially when there might are large numbers of changes between two passes, or when the pro-
grammer has only a poor idea as to what the changes might be. note-output-record-child- changedcan be more efficient for small changes at the bottom of the output record hierarchy,
or in cases where the programmer is well informed as to the specific changes necessary and can

Page 178	Table of Contents	Index	Page 180
	Chapters
	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 A, B, C, D, E