I mean to ask whether GIMP has anything resambling the Vector Layer Mask option in Photoshop.
Whereas layer masks let you create soft-edged masks in Photoshop CS6, vector masks create hard-edged masks defined by shapes created by a vector path on a layer. Vector-based shapes produce clean, smooth, and well-defined edges that are never jagged. And you can size and transform vector shapes without ever degrading the appearance of the element. You create a vector mask when you create a shape with any one of the shape tools. You can also create a vector mask when you convert type to a shape. (Choose Layer→Type→Convert to Shape.)