1. An interactive computing system comprising: an input for receiving a first series of depth images from a mobile depth camera when in motion and a second series of depth images from the mobile depth camera when static; a real-time camera tracking engine for tracking a position of the mobile depth camera when in motion; a dense 3D environment modeling system arranged to generate a dense 3D model of the environment from any of the series of depth images and position data from the real-time camera tracking engine; and an integration engine arranged to integrate at least a part of the dense 3D model into an application and to provide user input to the application by tracking real-time movement in a part of the environment using the second series of depth images, the integration engine being further arranged to: analyze the dense 3D model to identify objects in the model; when an object is identified, input object type information into the application; and adjust operation of the application based on the input object type information, wherein: the object comprises an active object and the integration engine is further arranged to adjust an output of the active object; the object comprises a display and the integration engine is further arranged to automatically calibrate a position of an object relative to the display based on a detected relative position of the display and the mobile depth camera; the integration engine is further arranged to adjust the output of another detected object; or the object comprises another depth camera and the integration engine is further arranged to calibrate the system based on a relative position of each depth camera.