With GL_OVR_multiview2 (vr.multiview), the scene is drawn once, from a
camera between the eyes whose view takes in both (plus a margin), into a
two-layer back buffer: every NV2A vertex program gets a two-view variant
that moves each view's clip position to its eye (x' = a x + b w + c, from
the shared view's and the eye's edges and the eye's place; nv2a_vsh.c),
screen-space geometry excepted. Sampling the back buffer meanwhile reads
the left eye's picture; visibility counts are halved. The host copies each
layer to its eye's image (host_xr_copy_layer_array).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
