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#!/usr/bin/env tclsh
## -*- tcl -*-
# testshadexy.tcl --
# Demonstrate how to mark data with a shaded background
#
# TODO:
# Command to get the (extreme) axis values from a plot
#
package require Plotchart
pack [canvas .c -width 400 -height 300]
set p [::Plotchart::createXYPlot .c {0.0 100.0 10.0} {-5.0 5.0 2.5}]
set x 0.0
set y 0.0
set xbegin {}
set ybegin {}
set dx 5.0
set xold $x
set yold $y
while { $x < 100.0 } {
set y [expr {0.7 * $y + rand() - 0.5 }]
$p plot data $x $y
#
# Mark the areas where y decreases
#
if { $y < $yold && $xbegin == {} } {
set xbegin $xold
set ybegin $yold
}
if { $y > $yold && $xbegin != {} } {
$p object rectangle "shade" $xbegin -5.0 $xold 5.0 -tag shade -fill lightgreen -outline lightgreen
set xbegin {}
}
set xold $x
set yold $y
set x [expr {$x + $dx}]
}
#
# Do not forget the last one
#
if { $y > $yold && $xbegin != {} } {
$p object rectangle "shade" $xbegin -5.0 $xold 5.0 -tag shade -fill lightgreen -outline lightgreen
set xbegin {}
}
.c lower shade
#
# Show a legend and remove an entry ...
#
# Use a trick to get a rectangle for the shade entry in the legend
$p dataconfig shade -type rectangle -colour lightgreen
$p legend data "The data"
$p legend shade "The shading"
after 2000 {
$p removefromlegend shade
}
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