viridis.js

// 32-entry viridis lookup table. Generated by linear interpolation between
// the same 5 stops the Python build uses (renderer.py:cmap_viridis), so the
// browser demo matches the desktop demo byte-for-byte on uniform inputs.
//
// Stops:  [68,1,84] [59,82,139] [33,144,141] [94,201,98] [253,231,37]
const _VIRIDIS_STOPS = [
  [ 68,   1,  84],
  [ 59,  82, 139],
  [ 33, 144, 141],
  [ 94, 201,  98],
  [253, 231,  37],
];

function _buildViridisLUT(n) {
  const out = new Uint8Array(n * 3);
  for (let i = 0; i < n; i++) {
    const t = i / (n - 1);
    const idx = t * (_VIRIDIS_STOPS.length - 1);
    const lo = Math.floor(idx);
    const hi = Math.min(lo + 1, _VIRIDIS_STOPS.length - 1);
    const frac = idx - lo;
    const a = _VIRIDIS_STOPS[lo];
    const b = _VIRIDIS_STOPS[hi];
    out[i * 3 + 0] = Math.round(a[0] * (1 - frac) + b[0] * frac);
    out[i * 3 + 1] = Math.round(a[1] * (1 - frac) + b[1] * frac);
    out[i * 3 + 2] = Math.round(a[2] * (1 - frac) + b[2] * frac);
  }
  return out;
}

const VIRIDIS_LUT = _buildViridisLUT(64);