Originally implemented in ShaderToy; ported to raw WebGL here. I don't actually know computer graphics and today's best omniscient machine oracles are unhelpful for this, so this mostly relies on trial and error and some vector maths I did on paper. Each ray in the viewport is intersected with planes in the xz, yz and xy directions. There are finitely many, since I don't know how or whether you can analytically compute the intersections for an infinite stack of them, so it is not, strictly, a "limitless" grid, though this is also true of the original and each plane is infinite in extent.