RectMask2D
矩形2D遮罩
A RectMask2D is a masking control similar to the Mask control. The mask restricts the child elements to the rectangle of the parent element. Unlike the standard Mask control it has some limitations, but it also has a number of performance benefits.
RectMask2D 是一种类似Mask控件的遮罩。mask把子元素限制在父元素的矩形区域中。和标准的Mask不同，它有一些限制，但是它也有很多性能上的好处。
Description
描述
A common use of a RectMask2D is to show small sections of a larger area. Using the RectMask2D to frame this area.
RectMask2D一个常见的用法是展示一张大图的一个小区域。使用RectMask2D去构建这个区域。
The limitations of RectMask2D control are:
RectMask2D空间的限制是：
- It only works in 2D space
- It will not properly mask elements that are not coplanar
- 它工作在2D空间
- 它不能正常地遮罩不在一个面上的元素
The advantages of RectMask2D are:
RectMask2D 的优点
- It does not use the stencil buffer
- No extra draw calls
- No material changes
- Fast performance
- 它没有使用模板缓冲
- 没有额外的Draw Calls
- 没有改变材质
- 更快的性能