| Category: | GUI Programming |
| Author/Contact Info | zentara@zentara.net |
| Description: | There was an "advanced perl programming" weekly contest awhile back( now defunct I think". One I entered was a roller coaster simulation. The original contest had various *.rc files to make any kind of coaster track design. I just included a nice one in DATA, to make the script self-contained. |
#!/usr/bin/perl
use warnings;
use strict;
use Tk;
# by zentara@zentara.net
# There was an advanced perl programming contest awhile
# back to simulate a roller coaster. This was my entry.
# This approach is a very simple method to simulate
# the roller-coaster motion. I didn't waste any time
# on actually computing the velocities or positions,
# rather I relied on the Law of Conservation of Energy,
# which says that the sum of the Kinetic and Potential
# Energies will remain constant. The initial total energy
# is the potential energy at the highest point, and that
# is released into kinetic energy( i.e. velocity) as the
# coaster drops. So as the coaster drops,
# it's KE increases, and as the coaster climbs it's KE
# decreases, and stalls if it climbs past it's start height.
#
# I figured this was the best approach, since we don't have
# an actual equation to differentiate to get the instantaneous
# values. So this is not mathematically exact, it ignores the
# constants in favor of better animation.
# After all, it's just a visual simulation,
$|++;
my %segs =();
my $count = 0; # holds how many segments there are
my $action = 0; # action flag
my $cur_loc = 1; # holds current segment in case of stop run
my $cur_ke = 0; # initial kinetic energy
my $g = 10; # gravitational acceleration
my $m = 1; # mass of coaster
# (left in for possible future Lorentz transforms
+ :-))
my $velocity = 0; # speedometer :-)
while(<DATA>){
$count++;
chomp;
next if /^\s*#/ || /^\s*$/; #skip comments and blank lines
my ($x, $y) = split(/\s+/, $_);
$segs{$count} = [$x, (400 - $y) ]; #inverse coords
}
my $mw = tkinit;
$mw->geometry("650x450+100+100");
my $canvas = $mw->Canvas(-width => 620, -height => 420,
-bg => 'black')->pack();
my @s;
foreach (1..$count){
my @str = ( ${$segs{$_}}[0], ${$segs{$_}}[1] );
push @s, @str;
}
my $curve = $canvas->createLine( @s,
-width => 5,
-smooth => 1,
-fill => 'lightgreen');
my $coaster = $canvas->createOval(${$segs{1}}[0] - 5,${$segs{1}}[1] -
+5,
${$segs{1}}[0] + 5 ,${$segs{1}}[1] +
+ 5,
-fill => 'yellow');
my $group = $canvas->createGroup([${$segs{1}}[0],${$segs{1}}[1]],
-members => [$coaster]);
my $subframe = $mw->Frame(-background =>'gray50')->pack(-fill => 'x');
$subframe->Button(-text =>'Exit',
-background => 'hotpink',
-activebackground => 'red',
-command => sub{ exit }
)->pack(-side=>'left',-padx=>40);
$subframe->Button(-text =>'Slower',
-background => 'lightyellow',
-activebackground => 'yellow',
-command => sub{ if($g < 3)
{ print chr(07);return}
else{$g *= .8; print "$g\n"; } } #not too slo
+w :-)
)->pack(-side=>'left',-padx=>40);
$subframe->Label(-text =>'Velocity ',
-background => 'black',
-foreground => 'green',
)->pack(-side=>'left');
$subframe->Label(-textvariable => \$velocity,
-width => 5,
-background => 'black',
-foreground => 'green',
)->pack(-side=>'left');
$subframe->Button(-text =>'Faster',
-background => 'lightgreen',
-activebackground => 'green',
-command => sub{ $g *= 1.25; print "$g\n"; }
)->pack(-side=>'left',-padx=>40);
my $actbut;
$actbut = $subframe->Button(-text =>'Start',
-background =>'lightsteelblue',
-activebackground =>'lightskyblue',
-command => sub { &action($cur_loc,$cur_ke) },
)->pack(-side=>'right',-padx=>40);
MainLoop;
######################################################################
+#
sub action {
if( $actbut->cget(-text) eq 'Start'){
$actbut->configure(-text=>'Stop');
$action = 1;
}else{
$actbut->configure(-text=>'Start');
$action = 0;
}
my ($cur_seg,$cur_ke,) = @_;
my $dt;
# potential energy at start
my $pe_max = $m*$g*(${$segs{1}}[1]);
#Energy is conserved so at any point
# pe_max = pe_current + ke_current
# so
# ke_current = pe_max - pe_current (both directly proportion to y)
while( $action ){
my $cur = $cur_seg;
my $cur_next = $cur_seg + 1;
if($cur_next > $count ){ $action = 0;
$actbut->configure(-text=>'Start');
$cur_next = 1;
}
my $x1 = ${$segs{$cur}}[0];
my $y1 = ${$segs{$cur}}[1];
my $x2 = ${$segs{$cur_next}}[0];
my $y2 = ${$segs{$cur_next}}[1];
my $dx = $x2 - $x1;
my $dy = $y2 - $y1;
my $distance = sqrt( $dx**2 + $dy**2);
# compute average y of segment
my $y_ave = ($y2 + $y1)/2;
$cur_ke = $m*$g*$y_ave - $pe_max;
#print "dy->$dy\tcur_ke->$cur_ke\n";
$canvas->move($group, $dx,$dy);
$canvas->update;
if($cur_next > $count ){ $cur_seg = 1}
else {$cur_seg++}
# velocity is proportional to the sqrt of ke
# and time is inverse to velocity
# $v = $distance/$seconds
# $seconds = $distance/$v
if($cur_ke >= 0){
my $v = sqrt(2*$cur_ke/$m);
$dt = $distance/$v; # constant 2 added for visual effect
if($cur_loc >= $count){
$cur_loc = 1;
$cur_ke = 0;
$dt = .001;
$velocity = 0;
}
$velocity = sprintf('%.1f',$v);
$velocity = sprintf('%.1f',$v);
#select(undef,undef,undef,$dt);
$mw->after($dt*1000,$canvas->update);
#it's not the best to use a blocking select in Tk
#but it's all in microseconds....so no problem
#select takes seconds , after takes microseconds
}else{
my $message =
'Uh oh, Out of KE, Get out and push. Hit Start to get moving.'
+ ;
$mw->messageBox(
-background => 'lightyellow',
-icon => 'error',
-message => $message,
-type => 'OK'
);
&restart;
}
$cur_loc = $cur_seg;
} #end of while loop
if($cur_loc >= $count){
$cur_loc = 1;
$cur_ke = 0;
$dt = .001;
$velocity = 0;
}
}
######################################################
sub restart{
$actbut->configure(-text=>'Start');
$action = 0; # action flag
$cur_loc = 1; # holds current segment in case of stop run
$cur_ke = 0; # initial kinetic energy
$g = 10;
}
####################################################
__DATA__
0 394
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4.71503160037539 374.563732945664
6.06061 369.017
8.64383766277946 359.356413328257
11.2270653255589 349.695826656515
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30.303 291.085
34.1461008917288 281.852959297317
36.3636 276.526
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48.4848 252.548
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54.5455 242.919
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60.6061 234.728
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157.576 226.994
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175.758 237.145
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200 250
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600 250
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| Replies are listed 'Best First'. | |
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Re: ztk-roller-coaster-simulation
by chanio (Priest) on Aug 10, 2005 at 04:40 UTC | |
by zentara (Archbishop) on Aug 10, 2005 at 11:22 UTC |
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