hexOffset function
A hexagon outline wave function spanning a period of 2 units.
Implementation
double hexOffset(num x) {
final mod = ((x + _oneSixth) % 2.0);
if (mod < _oneThird) return 0.5 - mod * 1.5;
if (mod < 1) return 0;
if (mod < 1 + _oneThird) return (mod - 1) * 1.5;
return 0.5;
}