Convert from the item based scroll units to logical pixels.
Source
double get pixelsPerScrollUnit {
final RenderBox box = context.findRenderObject();
if (box == null || !box.hasSize)
return 0.0;
switch (config.scrollDirection) {
case Axis.horizontal:
return box.size.width;
case Axis.vertical:
return box.size.height;
}
assert(config.scrollDirection != null);
return null;
}