Making the pattern between the patterns

The page stages three "stations" of the same law — line-on-line, ring-on-ring, and the dot-lattice twist — cycling on an eight-second clock through one big framed field. One grating of each pair breathes through a slow, eased rotation (or centre-offset, for the rings), and the moiré fringes do all the visible moving. A violet dimension bracket rides the field, live-typing the fringe period D = p / 2·sin(θ/2) as it stretches and collapses: the caption line for the pattern between the patterns.

Op-art discipline argues near-monochrome: the fringes are luminance phenomena, and any colour laid under them would fight the interference. Gallery white and grating ink carry the whole field; one violet is reserved for measurement marks and small accents — the instrument's ink, never the artwork's; a cool grey handles captions.

Pure SVG geometry, no filters, no raster. Each master grating is drawn once in <defs> and instanced twice with <use>: the line comb is a single <path> of 266 vertical strokes (one DOM node, not 266), the bullseye is 120 concentric circles, and the dot lattice is 130 lines wearing stroke-dasharray: 0 13 with round caps — dots as pure stroke geometry, no thirteen thousand circle nodes. Total stage weight stays under ~600 elements, so the browser composites the rotation instead of re-rasterising a pattern tile every frame.

The signature element — fringes sweeping from an invisible cause — is one transform: the second <use> sits in a group whose rotation breathes through a shaped sine (sign(s)·|s|^0.75, periods 15–18 s) so it dwells at the extremes like held breath. The fringe period is computed each frame from the true formula and drives the violet bracket's height and label, so the annotation is measured, not decorative. Moving the pointer across the stage adds a ±0.7° bias to the hidden rotation — the page quietly hands you the grating. Everything pauses on document.hidden, deltas are clamped, and prefers-reduced-motion renders each station settled mid-sweep at its most photogenic angle, tabs still working, nothing blank.