MaskNode 
  Creates a GskRenderNode that will mask a given node by another.
The @mask_mode determines how the 'mask values' are derived from the colors of the @mask. Applying the mask consists of multiplying the 'mask value' with the alpha of the source.
Return
A new GskRenderNode
Since
4.10
Parameters
source
The source node to be drawn
mask
The node to be used as mask
maskMode 
The mask mode to use