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（灯到结束阴影点）减去第一个距离（灯到开始阴影点），你得到从定位器间到光源处有多远距离。