A method of 3D printing, comprising the steps of: running a videogame, in turn comprising a step of generating a virtual game environment comprising in-game geometry; receiving an indication that the current state of the virtual game environment has been selected for 3D printing; obtaining supplementary geometry (222A,B,C,D); and supplementing the in-game geometry with the supplementary geometry to create a 3D printer geometry; in which components of the virtual game environment included in the 3D printer geometry are modified by the supplementary geometry to have structural features within the 3D printer geometry that have dimensions calculated to support the model in its final printed physical form; and characterised in that the step of obtaining supplementary geometry comprises: procedurally generating supplementary geometry (222A,B,C,D) according to one or more generative rules responsive to the current state of the virtual game environment; and associating supplementary geometry indicator data with the in-game geometry that is indicative of where to place supplementary support structures within the 3D printed model; and wherein the supplementary geometry indicator data is associated with the in-game geometry by one or more selected from the list consisting of: i. meta-data associated with one or more polygons of a virtual object; and ii. embedding indicator data within texture data. running a videogame, in turn comprising a step of generating a virtual game environment comprising in-game geometry; receiving an indication that the current state of the virtual game environment has been selected for 3D printing; obtaining supplementary geometry (222A,B,C,D); and supplementing the in-game geometry with the supplementary geometry to create a 3D printer geometry; in which components of the virtual game environment included in the 3D printer geometry are modified by the supplementary geometry to have structural features within the 3D printer geometry that have dimensions calculated to support the model in its final printed physical form; and characterised in that the step of obtaining supplementary geometry comprises: procedurally generating supplementary geometry (222A,B,C,D) according to one or more generative rules responsive to the current state of the virtual game environment; and associating supplementary geometry indicator data with the in-game geometry that is indicative of where to place supplementary support structures within the 3D printed model; and wherein the supplementary geometry indicator data is associated with the in-game geometry by one or more selected from the list consisting of: i. meta-data associated with one or more polygons of a virtual object; and ii. embedding indicator data within texture data. procedurally generating supplementary geometry (222A,B,C,D) according to one or more generative rules responsive to the current state of the virtual game environment; and associating supplementary geometry indicator data with the in-game geometry that is indicative of where to place supplementary support structures within the 3D printed model; and wherein the supplementary geometry indicator data is associated with the in-game geometry by one or more selected from the list consisting of: i. meta-data associated with one or more polygons of a virtual object; and ii. embedding indicator data within texture data. i. meta-data associated with one or more polygons of a virtual object; and ii. embedding indicator data within texture data.