A head mounted display, HMD, device operable by a user in a physical environment, comprising: one or more processors; a sensor package; a see-through display configured for rendering a mixed reality environment to the user, a view position of the user for the rendered mixed-reality environment being variable depending at least in part on a pose of the user's head in the physical environment; and one or more memory devices, wherein the one or more processors are coupled to the sensor package, the display and the one or more memory devices, the one or more memory devices are configured to store computer-readable instructions which, when executed by the one or more processors of the HMD device, perform a method comprising the steps of: positioning a three-dimensional, 3D, virtual viewport in the mixed-reality environment displayed on the display, wherein the 3D virtual viewport comprises a 3D bounding box defining where a 3D model in the mixed-reality environment is displayed by the HMD device, supporting extensibility to a 3D modeling application executing on a remote computing platform, the application for modelling an object and displaying the modelled object on a 2D monitor of the remote computing system, by receiving extensibility data from a remote computing platform over a network connection, the extensibility data including scene data describing the modelled object and user interface data describing user inputs to the remote computing platform associated with the modelled object, and rendering in the virtual viewport displayed on the display of the HMD device, during the user of the HMD device using the application on the remote computing platform, a 3D model of the modelled object based on the received scene data and user interface data, wherein the 3D model is independently rendered in the virtual viewport of the mixed-reality environment by the one or more processors on the display of the HMD device from the modeled object displayed on the 2D monitor of the remote computing platform, the 2D monitor of the remote computing platform being viewable through the display of the HMD device in the mixed-reality environment. one or more processors; a sensor package; a see-through display configured for rendering a mixed reality environment to the user, a view position of the user for the rendered mixed-reality environment being variable depending at least in part on a pose of the user's head in the physical environment; and one or more memory devices, wherein the one or more processors are coupled to the sensor package, the display and the one or more memory devices, the one or more memory devices are configured to store computer-readable instructions which, when executed by the one or more processors of the HMD device, perform a method comprising the steps of: positioning a three-dimensional, 3D, virtual viewport in the mixed-reality environment displayed on the display, wherein the 3D virtual viewport comprises a 3D bounding box defining where a 3D model in the mixed-reality environment is displayed by the HMD device, supporting extensibility to a 3D modeling application executing on a remote computing platform, the application for modelling an object and displaying the modelled object on a 2D monitor of the remote computing system, by receiving extensibility data from a remote computing platform over a network connection, the extensibility data including scene data describing the modelled object and user interface data describing user inputs to the remote computing platform associated with the modelled object, and rendering in the virtual viewport displayed on the display of the HMD device, during the user of the HMD device using the application on the remote computing platform, a 3D model of the modelled object based on the received scene data and user interface data, wherein the 3D model is independently rendered in the virtual viewport of the mixed-reality environment by the one or more processors on the display of the HMD device from the modeled object displayed on the 2D monitor of the remote computing platform, the 2D monitor of the remote computing platform being viewable through the display of the HMD device in the mixed-reality environment. positioning a three-dimensional, 3D, virtual viewport in the mixed-reality environment displayed on the display, wherein the 3D virtual viewport comprises a 3D bounding box defining where a 3D model in the mixed-reality environment is displayed by the HMD device, supporting extensibility to a 3D modeling application executing on a remote computing platform, the application for modelling an object and displaying the modelled object on a 2D monitor of the remote computing system, by receiving extensibility data from a remote computing platform over a network connection, the extensibility data including scene data describing the modelled object and user interface data describing user inputs to the remote computing platform associated with the modelled object, and rendering in the virtual viewport displayed on the display of the HMD device, during the user of the HMD device using the application on the remote computing platform, a 3D model of the modelled object based on the received scene data and user interface data, wherein the 3D model is independently rendered in the virtual viewport of the mixed-reality environment by the one or more processors on the display of the HMD device from the modeled object displayed on the 2D monitor of the remote computing platform, the 2D monitor of the remote computing platform being viewable through the display of the HMD device in the mixed-reality environment.