Select the shape layer, or mask shape layer, that you want to convert.
In the Canvas Layer Editor window, choose Edit > Rasterize Layer.
If the active shape layer was an image shape layer, a new image layer is created containing a painted representation of the shape.
If the active shape layer was a mask shape layer, a new mask layer is created containing a painted representation of the shape.
The original shape layer is deleted.
To convert an individual shape within a shape layer into paint, first re-create the shape on its own shape layer. Then convert the shape layer to an image layer.