Disclosed herein are apparatus, devices, and methods to provide a modified-transmissivity zone on a projection surface used to generate a virtual image superimposed onto a real-world view. In particular, a variable-transmissivity material may be provided in the projection surface. The transmissivity of variable-transmissivity material may be modified responsive to application of a stimulus. A stimulus source may be configured to selectively apply a stimulus to the variable-transmissivity material to generate a discrete modified-transmissivity zone on the projection surface.