layer.borderRadius

Rounds the corners of a layer in pixels. To create circles, set the property to a high value (50-100) or divide the layers width/height by two.
译：舍入的层中的像素的角落。要创建圆，该属性设置为高值（50-100）或分割层宽度/高度除以2。

layerA = new Layer
layerA.borderRadius = 3

# To create a circle: 
layerA.borderRadius = layerA.width/2