I built a Metal viewer on iPhone that re-lights an already-captured 3D scene with any lighting you like. Swap or rotate the HDR environment map, and the object's reflections follow in real time, with that environment also drawn into the background. Why relighting is valuable (the practical, commercial meaning) Ordinary Gaussian Splatting has the lighting from capture time baked in. So if you place the captured object somewhere else, the highlights and shadows clash with the new surroundings and look fake. Relighting strips that light off and returns it to material , so you can place the captured object under any lighting. This matters in practice: E-commerce / product visuals : capture a product once and show it under any light — showroom, outdoors, the customer's room (AR). Strong for "texture sells" goods like furniture, cars, jewelry, sneakers. Film / virtual production : place a real capture into a new scene, consistent with that scene's lighting (HDRI / LED wall). No reshoot.…