Abstract: A method of determining a tool path for controlling a printing tool, including step (401) of receiving an input file containing data indicative of a three-dimensional structure to be formed. At step (404) the structure is divided into a plurality of build layers, which are separated in a build direction and each layer extends laterally relative to the build direction. Each layer includes an external contour defining the intersection of the layer with an exterior surface of the three-dimensional structure. Step (405) defines a tool path, which fills the three-dimensional structure, wherein the path includes partially filling one or more higher build layers along the build direction before entirely filling at least one lower build layer. At step (406), a printing tool control algorithm is generated that includes a series of control commands for controlling the printing tool to move along the tool path to form the three-dimensional structure.