There's a bug till PHP 4.0.4 in this function. You can only draw vertical dashed lines. To draw other dashed lines you can set <ImageSetStyle> to a special dashed line and draw it by <ImageLine>.
Sample code:
<?php
function MDashedLine($image, $x0, $y0, $x1, $y1, $fg, $bg)
{
$st = array($fg, $fg, $fg, $fg, $bg, $bg, $bg, $bg);
ImageSetStyle($image, $st);
ImageLine($image, $x0, $y0, $x1, $y1, IMG_COLOR_STYLED);
}
?>