Hi!
I'm copying right from my SWF module with some changes; you will have to do some analyzing and reformating.
It draws a polygon, given radius and number of sides. No GD by the way, but the algorithm should be applicable elsewhere.

AGAIN: Just to illustrate one way to draw a polygon. The code below will not run!!

sub polygon {

     
        my $r = shift;
            my $sides = shift;        

        #Angles:
        my $theta = &rad(360/$sides);
        my $theta_half = &rad(180/$sides);
        #my $phase = &rad(0) ;
         my $beta = &rad ( (180-360/$sides) /2 ) ;
         my $s = $r * sin($theta)/sin($beta);
         my( $beginX,$beginY) = @M;
        my($sX,$sY);
        
        #Drawing:
            for  ( 1..$sides ) {
                 
                  $sX =  $s * cos(($_* $theta + $theta_half ));
                  $sY = $s * sin(($_* $theta + $theta_half ));
                  
                 $shapeSWF->drawLineTo($beginX+$sX,$beginY+$sY);
                  $beginX = $beginX+$sX;
                 $beginY = $beginY+$sY;
            } 
     }
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