An apparatus for displaying a virtual scene comprises a display wearable on a user's head and a graphics controller configured to calculate, from scene data representing the virtual scene, image data for the display such that the virtual scene is displayed in the environment irrespective of the head's position and pointing direction, the virtual scene appearing in the image data in a region of scene, wherein the graphics controller is configured to modulate excitation signals of a Lissajous scanning mirror assembly, which diverts the light beam of a light source, by modulation signals which are dependent on the region of scene.