position有9个点：lt,mt,rt,lm,mm,rm,lb,mb,rb，其实对应的是几个英文：lt(left top),mt(middle top),rt(right top)，以此类推
上官方原图：
OK，然后我们看一下他的代码是怎么写的，如果有人涉及到也可以借鉴：
<?php
/**
* Calculate the left top positions of a layer inside a parent layer container
* $position: http://phpimageworkshop.com/doc/22/corners-positions-schema-of-an-image.html
*
* @param integer $containerWidth
* @param integer $containerHeight
* @param integer $layerWidth
* @param integer $layerHeight
* @param integer $layerPositionX
* @param integer $layerPositionY
* @param string $position
*
* @return array
*/
public static function calculatePositions($containerWidth, $containerHeight, $layerWidth, $layerHeight, $layerPositionX, $layerPositionY, $position = 'LT')
{
$position = strtolower($position);
if ($position == 'rt') {
$layerPositionX = $containerWidth - $layerWidth - $layerPositionX;
} elseif ($position == 'lb') {
$layerPositionY = $containerHeight - $layerHeight - $layerPositionY;
} elseif ($position == 'rb') {
$layerPositionX = $containerWidth - $layerWidth - $layerPositionX;
$layerPositionY = $containerHeight - $layerHeight - $layerPositionY;
} elseif ($position == 'mm') {
$layerPositionX = (($containerWidth - $layerWidth) / 2) + $layerPositionX;
$layerPositionY = (($containerHeight - $layerHeight) / 2) + $layerPositionY;
} elseif ($position == 'mt') {
$layerPositionX = (($containerWidth - $layerWidth) / 2) + $layerPositionX;
} elseif ($position == 'mb') {
$layerPositionX = (($containerWidth - $layerWidth) / 2) + $layerPositionX;
$layerPositionY = $containerHeight - $layerHeight - $layerPositionY;
} elseif ($position == 'lm') {
$layerPositionY = (($containerHeight - $layerHeight) / 2) + $layerPositionY;
} elseif ($position == 'rm') {
$layerPositionX = $containerWidth - $layerWidth - $layerPositionX;
$layerPositionY = (($containerHeight - $layerHeight) / 2) + $layerPositionY;
}
return array(
'x' => $layerPositionX,
'y' => $layerPositionY,
);
}END;
