calculate_scale_hero.dart

final _scaleStart = 1.1;	
final _scaleEnd = 1.0;	

double _calculateScale(double currentScrollPosition) {	
  final startPointInPx = 0.0;	
  final endPointInPx = heroImageHeight - topBarHeight;	
  final distanceInPx = endPointInPx - startPointInPx;	
  final progressInPx = currentScrollPosition - startPointInPx;	
  final progress = progressInPx / distanceInPx;	
  final rawScale = _scaleStart - (progress * (_scaleStart - _scaleEnd));	
  return rawScale.clamp(_scaleEnd, _scaleStart);	
}