1. On a computing device, a method comprising: detecting via image data received by the computing device a first posture of a context-setting input performed by a first hand of a user to trigger execution of a drawing program; in response to detecting the first posture of the context-setting input, sending to a display a holographic stereoscopic user interface for the drawing program positioned based on a virtual interaction coordinate system, the virtual interaction coordinate system comprising a reference plane positioned based upon a position of the first hand of the user; detecting via image data received by the computing device a change in the first posture to a second posture of the context-setting input performed by the first hand, and in response, triggering a sub-context for the drawing program to detect drawing input; detecting via image data received by the computing device a drawing input performed by a second hand of the user relative to the holographic stereoscopic user interface and relative to the reference plane within the virtual reference coordinate system, the drawing input performed while the first hand of the user is performing the second posture of the context-setting input; and displaying a drawing in the holographic stereoscopic user interface based on the drawing input relative to the reference plane within the virtual interaction coordinate system.