neilwatson has asked for the wisdom of the Perl Monks concerning the following question:

Fellow monks, please consider this code: 
      2 use strict;
      3 use GD;
      4
      5 my $length = 2; #number of repeats
      6 my $image = new GD::Image($length*37+1,13);
      7 my $white = $image->colorAllocate(200,200,200);
      8 #$image->transparent($white);
      9 my $yellow = $image->colorAllocate(255,255,0);
     10 my $black = $image->colorAllocate(0,0,0);
     11 my ($x, @para1, @para2);
     12
     13 while ($x <= $length-1){
     14     $para1[$x] = new GD::Polygon;
     15     $para1[$x]->addPt(0+$x*12,0);
     16     $para1[$x]->addPt(12+$x*12,12);
     17     $para1[$x]->addPt(24+$x*12,12);
     18     $para1[$x]->addPt(12+$x*12,0);
     19
     20     $para2[$x] = new GD::Polygon;
     21     $para2[$x]->addPt(13+$x*12,0);
     22     $para2[$x]->addPt(25+$x*12,12);
     23     $para2[$x]->addPt(37+$x*12,12);
     24     $para2[$x]->addPt(25+$x*12,0);
     25
     26     $x++;
     27 }
     28
     29 while ($x >= 0){
     30     $image->filledPolygon($para1[$x], $black);
     31     $image->filledPolygon($para2[$x], $yellow);
     32
     33     $x--;
     34 }
     35 print $image->png();

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I'm am receiving this error Can't call method "length" on an undefined value at line 30

Can anyone offer some advice as to the cause? Neil Watson
watson-wilson.ca

Replies are listed 'Best First'.
Re: GD, arrays, and Polygons
by pfaut (Priest) on Mar 23, 2003 at 17:25 UTC

    You execute the first loop twice with $x set to 0 and 1. You build entries 0 and 1 in @para1 and @para2. When you leave the first loop, $x = 2. You then attempt to execute the second loop with $x set to 2 but you never defined that entry in the arrays. Move the decrement to the beginning of the loop.

    while ($x >= 0){
    $x--;
    $image->filledPolygon($para1[$x], $black);
    $image->filledPolygon($para2[$x], $yellow);
}

    [download]
    ---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';

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      Ack, I'm spending to much time performing Windows support. Thanks.

      Neil Watson
      watson-wilson.ca

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