Function blurf

external/.d3.js:180–199

(radius)

// integer, S[i - r - 1] and S[i + r + 1] are added to the sum, each weighted
// according to r - ⌊radius⌋.
function blurf(radius) {
  const radius0 = Math.floor(radius);
  if (radius0 === radius) return bluri(radius);
  const t = radius - radius0;
  const w = 2 * radius + 1;
  return (T, S, start, stop, step) => { // stop must be aligned!
    if (!((stop -= step) >= start)) return; // inclusive stop
    let sum = radius0 * S[start];
    const s0 = step * radius0;
    const s1 = s0 + step;
    for (let i = start, j = start + s0; i < j; i += step) {
      sum += S[Math.min(stop, i)];
    }
    for (let i = start, j = stop; i <= j; i += step) {
      sum += S[Math.min(stop, i + s0)];
      T[i] = (sum + t * (S[Math.max(start, i - s1)] + S[Math.min(stop, i + s1)])) / w;
      sum -= S[Math.max(start, i - s0)];
    }
  };
}

// Like blurf, but optimized for integer radius.
function bluri(radius) {