sample method
A new reading of the backdrop's luma under the bar. The first one takes effect at once; later ones after a moment, and animate.
Implementation
void sample(double luma) {
debugOnChange?.call(this, 'sample ${luma.toStringAsFixed(4)}');
if (!_sampled) {
_sampled = true;
_luma = luma;
_decide();
_snap();
return;
}
_pending.add((null, luma));
}