cairo:paint-with-alpha (cr alpha)

cr -- a cairo:context-t instance
alpha -- a number coerced to a double float for the alpha value, between 0.0 (transparent) and 1.0 (opaque)

A drawing operator that paints the current source everywhere within the current clip region using a mask of constant alpha value alpha. The effect is similar to the cairo:paint function, but the drawing is faded out using the alpha value.