BlendNode 
  Creates a GskRenderNode that will use @blend_mode to blend the @top node onto the @bottom node.
Return
A new GskRenderNode
Parameters
bottom
The bottom node to be drawn
top
The node to be blended onto the @bottom node
blendMode 
The blend mode to use
constructor(gskBlendNodePointer: <Error class: unknown class><<Error class: unknown class>>)(source)