fractionToIndex method
Convert a normalised fraction 0..1 to a data index in 0..dataLength-1.
Implementation
int fractionToIndex(double frac, int dataLength) {
if (dataLength <= 1) return 0;
final normalizedFraction = _sanitizeFraction(frac, fallback: 0);
return (normalizedFraction * (dataLength - 1)).round().clamp(
0,
dataLength - 1,
);
}