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#!/usr/local/bin/perl -w # Specify up to 2 numbers on the command line. The first is the # number of vertices you want the star to have (defaults to 5). # The second is the "magic number" you want to use when generating # the star (defaults to 2). A valid magic numbers is relatively # prime to the number of vertices. (play with it, you'll get the # idea) # # Ex: 11 5 > star.png use GD; use constant PI => # eh, good enough for government work... '3.1415926535897932384626433832795028841971693993751' . '058209749445923078164062862089986280348253421170680'; use constant STAR_SIZE => 200; use constant IMG_SIZE => STAR_SIZE * 2.2; # create a new image $im = new GD::Image(IMG_SIZE, IMG_SIZE); # allocate some colors $black = $im->colorAllocate(0,0,0); $blue = $im->colorAllocate(0,0,255); $im->fill(0,0,$black); # set background my $points = shift || 5; my $magic = shift || 2; my @vertices = &divide_circle(STAR_SIZE,$points); my $poly = &make_star($magic, \@vertices); die "not a valid magic number\n" unless defined $poly; # move to center of image $poly->offset(IMG_SIZE/2, IMG_SIZE/2); $im->polygon($poly,$blue); # make sure we are writing to a binary stream binmode STDOUT; # Convert the image to PNG and print it on standard output print $im->png; sub make_star { # given a "magic number" and a ref for an array of vertices # walks the vertices and constructs a GD::Polygon star using # those vertices and that magic number. # # returns undef if the magic number isn't really magic. my ($magic, $vertices) = @_; # make a copy of $verts so we can destroy it my @verts = @$vertices; my $poly = new GD::Polygon; for (my $i=0; defined $verts[$i]; $i = ($i + $magic) % scalar(@verts)) { my $point = $verts[$i]; $poly->addPt(@$point); $verts[$i] = undef; } # if there are still vertices left, # we don't have a valid magic number return undef if (grep { defined; } @verts); # we are good to go return $poly; } sub divide_circle { # given a radius and a number of points/vertices # return a list of x,y pairs that equally divide a circle # of that radius centered on 0,0 # (list context) my ($radius, $points) = @_; my @result; for ($i = 0; $i < $points; $i ++) { my $degree = $i * (360/$points); $degree += 180; # hush religious fanatics push @result, [ &get_point_on_circle($radius,$degree) ]; } return @result; } sub get_point_on_circle { # given a radius, and an angle (in degrees) returns an x,y pair # (list context) my ($radius, $degree) = @_; my $radian = $degree * (PI / 180); my $x = $radius * sin $radian; my $y = $radius * cos $radian; return ($x, $y); }

In reply to Make N pointed stars by hossman

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