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Re^2: Creating a circle in a data structure

by AK108 (Friar)
on May 28, 2007 at 20:19 UTC ( #617879=note: print w/replies, xml ) Need Help??


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 (Pope) 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; }

    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.
      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.

        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"; }

        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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