Various embodiments are provided herein for tracking a user's physical environment, to facilitate on-the-fly blending of a virtual environment with detected aspects of the physical environment. Embodiments can be employed to facilitate virtual roaming by compositing virtual representations of detected physical objects into virtual environments. A computing device coupled to a HMD can select portions of a depth map generated based on the user's physical environment, to generate virtual objects that correspond to the selected portions. The computing device can composite the generated virtual objects into an existing virtual environment, such that the user can traverse the virtual environment while remaining aware of their physical environment. Among other things, the computing device can employ various blending techniques for compositing, and further provide image pass-through techniques for selective viewing of the physical environment while remaining fully-immersed in virtual reality.