原文：
18.3. How can I do animations using after?
There is a "toggling button" demo script supplied with Tk called after_demo that makes effective use of after().
Terry Greenlaw mailto:terry@encompass.is.net of Encompass Technologies posted a character cell animator for the really bored. Here it is in a slightly modified form that allows string input from the command line (note too the recursive call that doesn't sop up system memory): #!/usr/bin/perl=head1 NAMEFrom: z50816@mip.lasc.lockheed.com "Terry Greenlaw" Thu Feb 1 12:02:24 EST 1996To: ptk@guest.WPI.EDUSubj: A code sample for the REALLY boredFor everyone with a case of Browser envy after using Microsoft's InternetExplorer, here's a perl/tk script only slightly more useful than a scriptto do <BLINK>. Don't know why I wrote it. Don't know why you'd run it.Maybe if you were writing a ticker tape application. Or had a weird thingfor Times Square. Anyway....togTerry Greenlaw (on-site @ Lockheed Martin) Encompass Technologiesz50816@mip.lasc.lockheed.com terry@encompass.is.net##################################################################=cut #!/usr/bin/perl #use strict; use Tk; $message=join(' ',@ARGV,''); if (!$message) { $message="THIS IS A VERY LONG SCROLLING MESSAGE... "; $topmssg="This is the top of the screen"; $botmssg="This is the bottom of the screen"; } else { $topmssg=$message; $botmssg=$message; } $top = MainWindow->new; $l1 = $top->Label(-fg => 'White', -text => $topmssg); $l1->pack(-fill => 'both', -expand => 1 ); $m1 = $top->Label(-fg=>'Red', -bg=>'black', -textvariable => \$message, -width => 15 ); $m1->pack(); $m2 = $top->Label(-wrap=>1, -fg=>'Green', -bg=>'black', -textvariable => \$message2, -width=>1, -height=>8 ); $m2->pack(-anchor=>'w'); $l2 = $top->Label(-fg => 'White', -text => $botmssg); $l2->pack(-fill => 'both', -expand => 1 ); after(100, \&scroll_it); $top->MainLoop; sub scroll_it { $message =~ /(.)(.*)/; $message="$2$1"; ($message2 = $message) =~ s/ / /g; after(100, \&scroll_it); } __END__
(Please note that a script like this is now distributed as "TickerTape" in your Tk*/Contrib/ directory.)
译文：
18.3. 如何用after来实现动画效果？
（译者注：原文提到的一个演示脚本after_demo现在好像已经没有了，不过我在自己系统的Tk安装目录里看到了一个名为after.htm的超文本，是专门介绍after和相关函数的用法的，也许对大家有用。）
为了这个确实很烦人的问题，Encompass Technologies（公司？）的Terry Greenlaw贴出了一个小的实现动画的例子。这里有一个稍加改动的版本，以允许从命令行输入字符串。（注意，这里的递归调用不会消耗系统内存的）
#!/usr/bin/perl
=head1 NAME
From: z50816@mip.lasc.lockheed.com "Terry Greenlaw" Thu Feb 1 12:02:24 EST 1996
To: ptk@guest.WPI.EDU
Subj: A code sample for the REALLY bored
对于所有使用浏览器并且忌妒微软的IE中的闪烁功能的人，这里的Perl/Tk脚本实现了<BLINK>的功能。我自己也不知道为什么要写这个脚本，我也不知道你为什么要运行它。也许你正在写一个类似自动滚动的应用程序，或者其它什么……
tog
Terry Greenlaw (on-site @ Lockheed Martin) Encompass Technologies
z50816@mip.lasc.lockheed.com terry@encompass.is.net
##################################################################
=cut
#!/usr/bin/perl
#use strict;
use Tk;
$message=join(' ',@ARGV,'');
if (!$message) {
$message="THIS IS A VERY LONG SCROLLING MESSAGE... ";
$topmssg="This is the top of the screen";
$botmssg="This is the bottom of the screen";
}
else {
$topmssg=$message;
$botmssg=$message;
}
$top = MainWindow->new;
$l1 = $top->Label(-fg => 'White', -text => $topmssg);
$l1->pack(-fill => 'both', -expand => 1 );
$m1 = $top->Label(-fg=>'Red', -bg=>'black',
-textvariable => \$message,
-width => 15
);
$m1->pack();
$m2 = $top->Label(-wrap=>1,
-fg=>'Green', -bg=>'black',
-textvariable => \$message2,
-width=>1, -height=>8
);
$m2->pack(-anchor=>'w');
$l2 = $top->Label(-fg => 'White', -text => $botmssg);
$l2->pack(-fill => 'both', -expand => 1 );
$top->after(100, \&scroll_it);
$top->MainLoop;
sub scroll_it {
$message =~ /(.)(.*)/;
$message="$2$1";
($message2 = $message) =~ s/ / /g; #（译者注：我不明白这个替换的目的是什么？）
$top->after(100, \&scroll_it);
}
__END__
