layer.originY < number>

Sets the y origin for scale, rotate and skew transformations. The origin is defined as a number, where 0 is the top edge of the layer and 1 the bottom edge. The default value is 0.5, the center of the layer.
译：设置规模，旋转和倾斜变换的起源。原点被定义为1和0之间的数，其中0是该层的顶部边缘和1的底部边缘。默认值是0.5，该层的中心。

layerA = new Layer
layerA.rotation = 45
layerA.originY = 0
layerA.originY = 1