# contribute by Heinrich Liesefeld hr.liesefeld@mx.uni-saarland.de
# First the program displays the default values Ð if you want to change anything, 
# type in the corresponding words that stand inside the brackets
# It then prompts you for the parameters you want to change.
# Afterwards you can enter the value you want to convert along 
# with the appropriate unit (cm, pix, or dg).
# It prints out the converted values.
# With ÒnÓ you restart the program to Êtype in another value 
# with the same settings or type ÒyÓ to change the settings. ÒxÓ ends the program

#default settings
$Bcm=36;              #visible display width in cm
$Ausg="20pix";        #start value in pix, dg oder cm
$Bpix=1024;           #resolution width in pixel
$Abst=70;             #distance between (the eyes of) the subject and the screen

&Settings;
&Input;
&Main;

sub Main {


if ($Ausg=~/dg/) {
  &UmrechnungSehcm;
  print "\nSize in centimeters:\t$Res$EinhRes\n";
  $Ausg=$Res.$EinhRes;
  &Umrechnungcmpix;
  print "Size in pixels:\t$Res$EinhRes\n\n";
  }

elsif ($Ausg=~/pix/) {
  &Umrechnungcmpix;
  print "\nSize in centimeters:\t$Res$EinhRes\n";
  $Ausg=$Res.$EinhRes;
  &UmrechnungSehcm;
  print "Size in degree:\t$Res$EinhRes\n\n";
  }

elsif ($Ausg=~/cm/) {
  &Umrechnungcmpix;
  print "\nSize in pixels:\t$Res$EinhRes\n";
  &UmrechnungSehcm;
  print "\nSize in degree:\t$Res$EinhRes\n\n";
  }

$weiterFr="\nChange settings? (y/n; escape: x): ";
print $weiterFr;
chomp($weiter=<STDIN>);
until ($weiter eq "y" or $weiter eq "n" or $weiter eq "x") {
  print $weiterFr;
  chomp($weiter=<STDIN>);
}
if ($weiter eq "y") {&Settings; &Input; &Main;}
elsif ($weiter eq "n") {&Input; &Main;}
elsif ($weiter eq "x") {print "\n\n";}

}



sub UmrechnungSehcm {
  $konst1=0.017453293; #1dg ist 0,017rad!
  $konst2=57.29577951;
  if ($Ausg=~/dg/) {
    ($Start)=substr ($Ausg, 0, length($Ausg)-2);
    $Start=($Start/2)*$konst1;
    $Res=2*$Abst*(sin($Start)/cos($Start));
    $EinhRes="cm";
    }

  elsif ($Ausg=~/cm/) {
    ($Start)=substr ($Ausg, 0, length($Ausg)-2);
    $x=2*$Abst;
    $Res=2*atan2 ($Start, $x);
    $Res=$Res*$konst2;
    $EinhRes="dg";
    }
  }

sub Umrechnungcmpix {
  if ($Ausg=~/cm/) {
    ($Start)=substr ($Ausg, 0, length($Ausg)-2);
    $Res=($Bpix/$Bcm)*$Start;
    $EinhRes="pix";
    }

  elsif ($Ausg=~/pix/) {
    ($Start)=substr ($Ausg, 0, length($Ausg)-3);
    $Res=($Bcm/$Bpix)*$Start;
    $EinhRes="cm";
    }
  }



sub Settings {
print "\nThe default settings are:\ndisplay width in cm [Bcm]: $Bcm\n";
print "display width in pixels [Bpix]: $Bpix\n";
print "distance from screen in cm [Abst]: $Abst\n";
print "If you want to change anything, type in the corresponding words inside the brackets: ";
chomp($Change=<STDIN>);

if ($Change=~/Bpix/i) {
  $BpixFr = "\nDisplay width in pixels:";
  print $BpixFr;
  chomp($Bpix=<STDIN>);
  while ($Bpix=~/[a-z]/) {
    print "\nJust type in a number (without unit)!";
    print $BpixFr;
    chomp($Bpix=<STDIN>);
    }
  }
if ($Change=~/Bcm/i) {
  $BcmFr = "\nDisplay width in cm:";
  print $BcmFr;
  chomp($Bcm=<STDIN>);
  while ($Bcm=~/[a-z]/) {
    print "\nJust type in a number (without unit)!";
    print $BcmFr;
    chomp($Bcm=<STDIN>);
    }
  }

if ($Change=~/Abst/i) {
  $AbstFr = "\nDistance from screen in cm:";
  print $AbstFr;
  chomp($Abst=<STDIN>);
  while ($Abst=~/[a-z]/) {
    print "\nJust type in a number (without unit)!";
    print $AbstFr;
    chomp($Abst=<STDIN>);
    }
  }
}


sub Input {
$Ausgfr = "\nInitial value in cm, dg or pix: ";
print $Ausgfr;
chomp($Ausg=<STDIN>);
until ($Ausg=~/cm/ or $Ausg=~/pix/ or $Ausg=~/dg/) {
  print "\nPlease add the unit as pixel (pix), angle of view (dg) or centimeter (cm) to the value!";
  print $Ausgfr;
  chomp($Ausg=<STDIN>);
  }
while ($Ausg=~/,/) {
  print "\nUse "." as decimal point!";
  print $Ausgfr;
  chomp($Ausg=<STDIN>);
  }
}