private function writeText(&$im, $x1, $y1, $x2, $y2, $message)
{
if (self::$white === null) {
self::$white = ImageColorAllocate($im, 255, 255, 255);
}
if (self::$black === null) {
self::$black = ImageColorAllocate($im, 0, 0, 0);
}
imagefilledrectangle($im, $x1, $y1, $x2, $y2, self::$black);
$box = imagettfbbox(self::$fontsize, 0, TN_FONT, $message);
$width = $box[4] - $box[0];
$height = $box[1] - $box[7];
$left = $x1 + ($x2 - $x1) / 2.0 - $width / 2;
$top = $y1 + ($y2 - $y1) / 2.0 + $height / 2;
imagettftext($im, 9, 0, $left, $top, self::$white, TN_FONT, $message);
}
