An agent distributor may be to selectively deliver agent at a first contone density and at a second contone density different from the first contone density respectively onto an interior portion and a surface portion of successive layers of build material in respective first and second patterns in accordance with data representing a three-dimensional object to be generated, so that the build material is to solidify to form slices of the three-dimensional object in accordance with the first and second patterns, and so that the three-dimensional object is to achieve a target surface roughness as a result of the second contone density of the second pattern.