1. One or more computer storage media storing computer-useable instructions that, when used by one or more computing devices, cause the one or more computing device to perform a method, the method comprising: receiving sensor data from one or more head-mounted display (HMD) on-board sensors; using the sensor data to determine an HMD wearer's head position and rotation relative to the HMD wearer's body and an environment surrounding the HMD wearer; classifying two or more regions within the HMD wearer's total field of view (TFOV) based on one or more pre-determined rules and the HMD wearer's head position and rotation relative to the HMD wearer's body and an environment surrounding the HMD wearer; and locating virtual images to be displayed by the HMD based on classifying the two or more regions within the HMD wearer's TFOV.