From one number to one knot
The only input is the clock of the Base chain: the timestamp of the current block. Nobody sets it and nobody can roll it back.
A day is that timestamp divided by 86,400, rounded down. That gives one calendar day in UTC, with the boundary at midnight UTC. The number itself counts days since 1 January 1970; day one of this project is day number 20701.
The seed is that day number run through splitmix64. From it you pull a stream of bits: eight bits pick the palette, then two bits for each of the 64 cells in an 8 by 8 grid.
Four cell states: two quarter-arcs in one of two orientations, a vertical pass, a horizontal pass. Classic Truchet has arcs and nothing else. The passes break it into longer runs.
The drawing is one SVG path drawn twice: a thicker shadow and a thinner cord. The whole file is about five kilobytes. The contract returns it as a data: URI, with no server in between.
The palette is one of eight: ink, copper, moss, ash, ultramarine, rust, salt, tar. This page takes its colors from today's palette, so it looks different in each of the eight epochs. Today: ultramarine.
Build it yourself
The same day number gives the same knot every time, ten years from now and with this page switched off. The generator is in the repository. The full random stream is below, so you can port it to any language.
u64 next(u64 x):
x += 0x9e3779b97f4a7c15
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9
x = (x ^ (x >> 27)) * 0x94d049bb133111eb
return x ^ (x >> 31)
counter = next(day_number)
palette = top8(next(++counter)) mod 8
cell[i] = top2(next(++counter)) for i in 0..63If you build it, write to me. That is the one thing I am waiting for here.