Underwater Caustics Simulator (2D)

This 2D top-down simulator ray-traces overhead sunlight through a physically modeled, ever-changing water surface — five superposed sine waves of different wavelength, direction and speed — refracting each ray at the air-water interface via Snell's law and following it down to a pool floor, where the accumulated density of ray landings paints the bright, shifting caustic network you'd see at the bottom of a real sunlit pool. Drag the amplitude slider to sharpen or soften the focusing, the speed slider to slow the pattern down to a near-still frame or set it rippling, and the depth slider to watch the same surface slopes paint a tight or a diffuse caustic net depending on how far the rays travel before they land.