Shaders, frame timing, and foveated rendering.
3 questions in AR/VR & Spatial Computing.
A headset draws to eyes that are still moving, so a late frame is presented in the wrong place for where the head now is; the world appears to slip, the vestibular and visual senses disagree, and the result is discomfort rather than a visual blemish. Reprojection hides it by re-warping the last good frame against a fresher pose.
Only the view and projection matrices differ between eyes, so scene traversal, culling, animation and shadow maps can be done once, and multiview rendering lets one draw call emit both views with a per-view matrix chosen in the vertex shader. What cannot be shared is anything computed in screen space.
Human acuity collapses away from the fovea, so a renderer can shade the periphery at a fraction of the centre's sample rate without a visible difference. Gaze-tracked variants follow the eye and save more; both save only pixel-shading work, so a CPU-bound or vertex-bound application gains nothing at all.