Bad index while coercing array into hash

[rbc]

Dear Monks,

I am stumped. What am I doing wrong here.

#!/usr/bin/perl -w

use lib ( '../Vector2D' );
use Vector2D;

my $POLYGONS_MAX_Y = 11;
my $A = new Vector2D(  2,  3 );
my $B = new Vector2D(  7,  1 );
my $C = new Vector2D( 13,  5 );
my $D = new Vector2D( 13, 11 );
my $E = new Vector2D(  7,  7 );
my $F = new Vector2D(  2,  9 );

my @AB = [ $A, $B ];
my @BC = [ $B, $C ];
my @CD = [ $C, $D ];
my @DE = [ $D, $E ];
my @EF = [ $E, $F ];
my @FA = [ $F, $A ];

my @polygon = ( @AB, @BC, @CD, @DE, @EF, @FA );

my @ET;  # global Edge Table
# each entry in the ET contains the Ymax coordinate of the edge,
# the x cooridnate of the bottom endpoint Xbot and the x increment 
# used in the stepping from one scan lime to the next 1/m
for my $edge (@polygon) {
        my $y    = ( @{$edge}->[0]->gety() <  @{$edge}->[1]->gety() ) 
+? @{$edge}->[0]->gety() : @{$edge}->[1]->gety() ;
        my $Ymax = ( @{$edge}->[0]->gety() >= @{$edge}->[1]->gety() ) 
+? @{$edge}->[0]->gety() : @{$edge}->[1]->gety() ;
        my $Xbot = ( @{$edge}->[0]->gety() <  @{$edge}->[1]->gety() ) 
+? @{$edge}->[0]->getx() : @{$edge}->[1]->getx() ;

        my $invSlope    = &calcOneOverSlope($edge);
        my $rec = {
                Ymax            => $Ymax,
                Xbot            => $Xbot,
                invSlope        => $invSlope
        };
        print "$y -> $Ymax | $Xbot | $invSlope\n";
        push( @{$ET[$y]}, $rec );
}

for my $i (1..$POLYGONS_MAX_Y) {
        if ( $ET[$i] ) {
                print "ET[$i] = ";
                for my $r ( ${ET[$i]} ) {
                        print "{" . $r->{Ymax} . "|" . $r->{Xbot} . "|
+" . $r->{invSlope} . "}" ;
                }
                print "\n";
        } else {
                print "ET[$i] = NULL\n";
        }
}

sub calcOneOverSlope {
        my $edge = shift;
        my $y = @{$edge}->[0]->gety()-@{$edge}->[1]->gety();
        my $x = @{$edge}->[0]->getx()-@{$edge}->[1]->getx();
        if ( $y == 0 ) { return undef; }
        return $x/$y;
}

When I execute this I get the following output and error message.

$ ./buildET.pl 
1 -> 3 | 7 | -2.5
1 -> 5 | 7 | 1.5
5 -> 11 | 13 | 0
7 -> 11 | 7 | 1.5
7 -> 9 | 7 | -2.5
3 -> 9 | 2 | 0
Use of uninitialized value in concatenation (.) or string at ./buildET.pl line 49.
Use of uninitialized value in concatenation (.) or string at ./buildET.pl line 49.
Bad index while coercing array into hash at ./buildET.pl line 49.
ET(1] = 

I had hoped that the output would look like this ...

ET(1] = {3 | 7 | -2.5} {5 | 7 | 1.5}
ET(2] = NULL
ET(3] = {9 | 2 | 0}
ET(4] = NULL
ET(5] = {11 | 13 | 0}
ET(6] = NULL
ET(7] = {11 | 7 | 1.5} {7 -> 9 | 7 | -2.5}
ET(8] = NULL
...
ET(20] = NULL

Line 49 is this line ...
  print "{" . $r->{Ymax} . "|" . $r->{Xbot} . "|" . $r->{invSlope} . "}" ; Thanks

Edited: ~Fri Sep 27 15:05:17 2002 (GMT) by footpad: s/<PRE>/<CODE>/; in last code line, per Consideration.

[fglock]

    for my $i (1..$POLYGONS_MAX_Y) {

- perl arrays start in "zero" by default. Try:

    for my $i (0..$POLYGONS_MAX_Y - 1) {

[rbc]

Thanks for the reply.
I tried it out now my output looks like so ...

1 -> 3 | 7 | -2.5
1 -> 5 | 7 | 1.5
5 -> 11 | 13 | 0
7 -> 11 | 7 | 1.5
7 -> 9 | 7 | -2.5
3 -> 9 | 2 | 0
ET(0] = NULL
Use of uninitialized value in concatenation (.) or string at ./buildET
+.pl line 49.
Use of uninitialized value in concatenation (.) or string at ./buildET
+.pl line 49.
Bad index while coercing array into hash at ./buildET.pl line 49.
ET(1] =

[chromatic]

You're looping over @ET 11 times when it only contains 6 elements.

[rbc]

Thanks be to the Gods for Data::Dumper.
Useing Data::Dumper's Dumper() sub should me the error of my ways!

I needed to be doing this ...


for my $i (1..$POLYGONS_MAX_Y) {
    if ( $ET[$i] ) {
        print "ET[$i] = ";
        for my $list ( ${ET[$i]} ) {
            for my $r ( @{$list} ) {
                print "{" . $r->{Ymax} . "|" . 
                            $r->{Xbot} . "|" . 
                            $r->{invSlope} . 
                      "}" ;
            }
        }
        print "\n";
    } else {
        print "ET[$i] = NULL\n";
    }
}

Also thank those monks that replied to my question.

Thanks!