<html> <head> </head>
<body>
<?php
if( !isset($_POST['startx']) || empty($_POST['startx']) || !isset($_POST['starty']) || empty($_POST['starty']) || !isset($_POST['endx']) || empty($_POST['endx']) || !isset($_POST['endy']) || empty($_POST['endy'])
)
{
print '<form action="' . $_SERVER['PHP_SELF'] . '" method="post">';
print "\n<br \>";
print 'Starting X Point<input name="startx" type="text">';
print "\n<br \>";
print 'Starting Y Point<input name="starty" type="text">';
print "\n<br \>";
print 'End X Point<input name="endx" type="text">';
print "\n<br \>";
print 'End Y Point<input name="endy" type="text">';
print "\n<br \>";
print '<input type="submit" /></form>';
print "\n<br \>";
}
else{
$startx = (int) htmlentities( $_POST['startx'] );
$starty = (int) htmlentities( $_POST['starty'] );
$endx = (int) htmlentities( $_POST['endx'] );
$endy = (int) htmlentities( $_POST['endy'] );
print "\n<br />";
print $startx . "," . $starty . " " . $endx . "," . $endy;
print "\n<br />";
print "width: " . ($endx - $startx);
print "\n<br />";
print "height: " . ($endy - $starty);
print "\n<br />";
print "acos(startx): " . acos($startx);
print "\n<br />";
} //end of if-else user filled in textarea
?>
</body></html>