update method
Update all of the Layers currently bound to the UI, regardless of
whether they're currently visible or not. The provided value, ds
, is the
elapsed time in (fractional) seconds since the last call to update.
You can use this value to provide consistent animations or game flow
regardless of the underlying framerate.
Implementation
void update(double ds) {
for (var i = 0; i < _layers.length; i++) {
_layers[i].update(ds);
}
}