in reply to Re: Creating a circle in a data structure
in thread Creating a circle in a data structure

I'll check this out soon, but I need to fight through converting it to Perl from C. This seems similar to Crackers2's method; hopefully it won't have the flaws.
  • Comment on Re^2: Creating a circle in a data structure

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Re^3: Creating a circle in a data structure
by BrowserUk (Patriarch) on May 29, 2007 at 03:50 UTC

    Try this. I'm not certain it's exactly equivalent to your original as I had some trouble understanding your 'drawing' code, but it's not far off. Your use of %curpass confused me as it seems unnecessary.

    You should be able to relate the sub genEndPoints() to the code at the end of the page I linked above. Rather than generating all the points on the circumference for all integer radii upto max radius, it generates only the endpoints (8 at a time using symmetry), of the raster lines required to 'fill' the circle and then draws those lines. Let me know if anything is unclear. 

    #!/usr/bin/perl

use strict;
use warnings;

use CGI ();
my $q = CGI->new;

# use CGI::Carp 'fatalsToBrowser';

my %circle;

my $prev_data;

# Read the previous circles
my @prev_circles;
{
    my @x_vals = $q->param('x');
    my @y_vals = $q->param('y');
    my @r_vals = $q->param('r');
    for(my $i = 0; $i < @r_vals; $i++) {
        foreach ($r_vals[$i], $x_vals[$i], $y_vals[$i]) {
            die "All values must be positive integers!\n" if /[^\d\.]/
        }
        push(@prev_circles, {
            r => $r_vals[$i],
            x => $x_vals[$i],
            y => $y_vals[$i],
        });
    }
}

sub genEndPoints {
    my( $radius, $xCenter, $yCenter ) = @_;

    my %endPoints;
    my( $x, $y, $p ) = ( 0, $radius, 1 - $radius );

    $endPoints{ $yCenter  } = [ $xCenter - $radius, $xCenter + $radius
+ ];
    while( $x < $y ) {
        $x++;
        if( $p < 0 ) {
            $p += 2 * $x + 1;
        } else {
            $y--;
            $p += 2 * ( $x - $y + 1 );
        }
        $endPoints{ $yCenter - $y  } = [ $xCenter - $x, $xCenter + $x 
+];
        $endPoints{ $yCenter + $y  } = [ $xCenter - $x, $xCenter + $x 
+];
        $endPoints{ $yCenter - $x  } = [ $xCenter - $y, $xCenter + $y 
+];
        $endPoints{ $yCenter + $x  } = [ $xCenter - $y, $xCenter + $y 
+];
    }
    return \%endPoints;
}

# 'Draw' the circle in the hash.
foreach my $circle (@prev_circles) {
    my $rmax     = $circle->{'r'};
    my $center_x = $circle->{'x'};
    my $center_y = $circle->{'y'};
    $prev_data .= qq~
    <input type="hidden" name="r" value="$rmax" />
    <input type="hidden" name="x" value="$center_x" />
    <input type="hidden" name="y" value="$center_y" />\n
    ~;

    my $endPoints = genEndPoints( $rmax, $center_x, $center_y );

    for my $y ( keys %{ $endPoints } ) {
        my( $startX, $endX ) = @{ $endPoints->{ $y } };
        for my $x ( $startX .. $endX ) {
            $circle{ $y }{ $x }++;
        }
    }
}

my $output = q~<html>
<head>
<title>A circle as a table</title>
<style type="text/css">
body {background: #888;}
.c1 {background: #000;}
.c2 {background: #008;}
.c3 {background: #00f;}
.c4 {background: #08f;}
.c5 {background: #0ff;}
.c6 {background: #8ff;}
.c7 {background: #fff;}
</style>
</head>
<body>
<table>
~;
foreach my $rowid (0 .. max(keys %circle)) {
    my $row = $circle{$rowid};
    $output .= "<tr>";
    foreach my $columnid (0 .. max(keys %{$row})) {
        my $column = $row->{$columnid};
        my $class = '';
        $column = 7 if $column > 7;
        $class = qq~ class="c$column"~ if $column;
        $output .= qq~<td$class></td>~;
    }
    $output .= "</tr>\n";
}

$output .= qq~
</table>
<br />
<br />
<form method="post" >
$prev_data
<br />New circle's radius: <input type="text" size="10" name="r" value
+="20" />
<br />New circle's center: (<input type="text" size="10" name="x" valu
+e="50" />,
<input type="text" size="10" name="y" value="50" />)
<br /><input type="submit" />
</form>
</body>
</html>
~;

print $q->header, $output;

sub max {
    my $max = 0;
    foreach (@_) { $max = $_ if $_ > $max; }
    return $max;
}

    [download]
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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      This is exactly what I was looking for. I was able to modify $circle{ $y }{ $x }++; to read $circle{ $y }{ $x } += int sqrt(($x - $center_x) ** 2 + ($y - $center_y) ** 2);. That color-codes the center going out (and would go to the edge of the circle, if I had enough CSS classes).

      My use of %curpass earlier was to ensure that any pixel in the original circle didn't get ++'d twice for the same circle entry.

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        That color-codes the center going out (and would go to the edge of the circle, if I had enough CSS classes).

        You could use the code from A hierarchy of color (intensity)? to generate your CSS classes to form a Color ramp. Below I've used 256 which seems to strike the best balance between smoothness and rendering speed.

        I also added cellspacing=0 to the table definition as it much improves the appearance. 

        sub colorRamp {
    my( $v, $vmin, $vmax ) = @_;
    my( $r, $g, $b ) = (1) x 3;
    $v = $vmax if $v > $vmax;
    $v = $vmin if $v < $vmin;

## Uncomment below to invert the color range
    $v = $vmax + $vmin - $v;

    my $dv = $vmax - $vmin;
    if( $v < ( $vmin + 0.25*$dv ) ) {
        $r = 0;
        $g = 4 * ($v - $vmin) / $dv;
    }
    elsif( $v < ( $vmin + 0.5 * $dv ) ) {
        $r = 0;
        $b = 1 + 4 * ($vmin + 0.25 * $dv - $v) / $dv;
    }
    elsif( $v < ( $vmin + 0.75 * $dv ) ) {
        $r = 4 * ($v - $vmin - 0.5 * $dv) / $dv;
        $b = 0;
    }
    else {
        $g = 1 + 4 * ($vmin + 0.75 * $dv - $v) / $dv;
        $b = 0;
    }
    return sprintf "#%02x%02x%02x", $r*255, $g*255, $b*255;
}

my $ColorRange = 255;

my $styles = '';
$styles .= sprintf ".c%d { background:%s;}\n",
    $_, colorRamp( $_, 0, $ColorRange )
    for 0 .. $ColorRange;

my $output = qq~<html>
<head>
<title>A circle as a table</title>
<style type="text/css">
body {background: #888;}
$styles
</style>
</head>
<body>
<table cellspacing=0 >
~;

foreach my $rowid (0 .. max(keys %circle)) {
    my $row = $circle{$rowid};
    $output .= "<tr>";
    foreach my $columnid (0 .. max(keys %{$row})) {
        my $column = $row->{$columnid};
        my $class = '';
        $column = $ColorRange if $column > $ColorRange;
        $class = qq~ class="c$column"~ if $column;
        $output .= qq~<td$class></td>~;
    }
    $output .= "</tr>\n";
}

        [download]

        Is your purpose to generate the structure and the table graphic is just a way of demonstrating it? Or is the display of the result the real objective?

        If the latter, it would probably be much faster and use less bandwidth to render to a .png using GD(or similar) and then link the image.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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