The most bold-line-functions i found have problems with lines in a certian direction (they draw smaller lines with some angles). To do a real bold line just use this function:
<?php
function imageBoldLine($resource, $x1, $y1, $x2, $y2, $Color, $BoldNess=2, $func='imageLine')
{
$center = round($BoldNess/2);
for($i=0;$i<$BoldNess;$i++)
{
$a = $center-$i; if($a<0){$a -= $a;}
for($j=0;$j<$BoldNess;$j++)
{
$b = $center-$j; if($b<0){$b -= $b;}
$c = sqrt($a*$a + $b*$b);
if($c<=$BoldNess)
{
$func($resource, $x1 +$i, $y1+$j, $x2 +$i, $y2+$j, $Color);
}
}
}
}
?>
