In the Canvas Layer Editor window select the shape layer and choose Edit > Rasterize Layer.
After you have finalized a shape, you may want to convert it into paint. You do this by converting the shape layer into an image layer. You cannot convert an individual shape within a shape layer into paint.
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.
To convert a shape layer into an image layer (and delete the original shape 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.
