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.\" ========================================================================
.TH Tk::Trace 3 "2000-12-30" "Tk800.023" "perl/Tk Documentation"
Tk::Trace \- emulate Tcl/Tk \fBtrace\fR functions.
\& $mw->traceVariable(\e$v, 'wru' => [\e&update_meter, $scale]);
\& %vinfo = $mw->traceVinfo(\e$v);
\& print "Trace info :\en ", join("\en ", @{$vinfo{-legible}}), "\en";
\& $mw->traceVdelete(\e$v);
This class module emulates the Tcl/Tk \fBtrace\fR family of commands by
binding subroutines of your devising to Perl variables using simple
\&\fBTie::Watch\fR features.
Callback format is patterned after the Perl/Tk scheme: supply either a
code reference, or, supply an array reference and pass the callback
code reference in the first element of the array, followed by callback
User callbacks are passed these arguments:
\& $_[0] = undef for a scalar, index/key for array/hash
\& $_[1] = variable's current (read), new (write), final (undef) value
\& $_[2] = operation (r, w, or u)
\& $_[3 .. $#_] = optional user callback arguments
As a Trace user, you have an important responsibility when writing your
callback, since you control the final value assigned to the variable.
A typical callback might look like:
\& my($index, $value, $op, @args) = @_;
\& # .... code which uses $value ...
\& return $value; # variable's final value
Note that the callback's return value becomes the variable's final value,
for either read or write traces.
For write operations, the variable is updated with its new value before
Only one callback can be attached to a variable, but read, write and undef
operations can be traced simultaneously.
.IP "$mw\->traceVariable(varRef, op => callback);" 4
.IX Item "$mw->traceVariable(varRef, op => callback);"
\&\fBvarRef\fR is a reference to the scalar, array or hash variable you
wish to trace. \fBop\fR is the trace operation, and can be any combination
of \fBr\fR for read, \fBw\fR for write, and \fBu\fR for undef. \fBcallback\fR is a
standard Perl/Tk callback, and is invoked, depending upon the value of
\&\fBop\fR, whenever the variable is read, written, or destroyed.
.ie n .IP "%vinfo = $mw\->traceVinfo(varRef);" 4
.el .IP "%vinfo = \f(CW$mw\fR\->traceVinfo(varRef);" 4
.IX Item "%vinfo = $mw->traceVinfo(varRef);"
Returns a hash detailing the internals of the Trace object, with these
\& -value => 'HELLO SCALAR'
\& -legible => above data formatted as a list of string, for printing
For array and hash Trace objects, the \fB\-value\fR key is replaced with a
\&\fB\-ptr\fR key which is a reference to the parallel array or hash.
Additionally, for an array or hash, there are key/value pairs for
all the variable specific callbacks.
.IP "$mw\->traceVdelete(\e$v);" 4
.IX Item "$mw->traceVdelete($v);"
Stop tracing the variable.
\& # Trace a Scale's variable and move a meter in unison.
\& $mw = MainWindow->new;
\& $c = $mw->Canvas(qw/-width 200 -height 110 -bd 2 -relief sunken/)->grid;
\& $c->createLine(qw/100 100 10 100 -tag meter/);
\& $s = $mw->Scale(qw/-orient h -from 0 -to 100 -variable/ => \e$v)->grid;
\& $mw->Label(-text => 'Slide Me for 5 Seconds')->grid;
\& $mw->traceVariable(\e$v, 'w' => [\e&update_meter, $s]);
\& $mw->after(5000 => sub {
\& print "Untrace time ...\en";
\& %vinfo = $s->traceVinfo(\e$v);
\& print "Watch info :\en ", join("\en ", @{$vinfo{-legible}}), "\en";
\& $c->traceVdelete(\e$v);
\& my($index, $value, $op, @args) = @_;
\& $min = $s->cget(-from);
\& $pos = $value / abs($max - $min);
\& $x = 100.0 - 90.0 * (cos( $pos * $pi ));
\& $y = 100.0 - 90.0 * (sin( $pos * $pi ));
\& $c->coords(qw/meter 100 100/, $x, $y);
\& Stephen.O.Lidie@Lehigh.EDU, Lehigh University Computing Center, 2000/08/01
\& . Version 1.0, for Tk800.022.
Copyright (C) 2000 \- 2000 Stephen O. Lidie. All rights reserved.
This program is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
projects / OpenSPARC-T2-DV / blob