The disclosed special-purpose hardware device may include an image signal processor that receives, from a camera device of a head-mounted-display system, image frames of a physical environment. The special-purpose hardware device may also include a positional tracking component that (1) stores at least a portion of the image frames in a cache of the special-purpose hardware device that has a faster access speed than a main memory of the special-purpose hardware device, (2) tracks, based on the portion of the image frames stored in the cache, a change in the position of the head-mounted display system within the physical environment, and (3) stores the change in the position of the head-mounted-display system in the main memory for use in generating one or more augmented-reality frames. The special-purpose hardware device may further include a frame-output interface that feeds the augmented-reality frames to a display device of the head-mounted-display system.