By subtracting the first distance( light to startShadow locator) from the second distance( light to endShadow locator), you get the difference between how far the locators are from the light source.

• 通过第二个距离（到结束阴影点）去第一个距离（到开始阴影点）你得到从定位器间到光源处有多远距离。