Function paethRef

packages/engine/src/utils/alphaBlit.test.ts:169–177

(a: number, b: number, c: number)

// filter type so the defilter logic gets actual coverage.

const paethRef = (a: number, b: number, c: number): number => {
  const p = a + b - c;
  const pa = Math.abs(p - a);
  const pb = Math.abs(p - b);
  const pc = Math.abs(p - c);
  if (pa <= pb && pa <= pc) return a;
  if (pb <= pc) return b;
  return c;
};

/**
 * Build a PNG with a specific filter type applied to every row. Encodes a