loading_backdrop (screen shader)

A calm, slowly drifting full-screen backdrop for the world loading screen. A deep near-black field carries two large, soft glows that move along slow independent orbits, finished with a gentle vignette and a faint animated grain that keeps the gradient from banding. Animation is driven entirely by engine.time, so it advances on its own during boot with no per-frame uniform updates. It is quiet by design, so it sits behind the world's cover image, title, and progress bar. Drawn through the backgroundShader UI style after registration with ui.registerBackgroundShader.