extentInside property

double extentInside

The quantity of visible content.

If extentBefore and extentAfter are non-zero, then this is typically the height of the viewport. It could be less if there is less content visible than the size of the viewport.

Implementation 

double get extentInside {
  return math.min(pixels, maxScrollExtent) -
         math.max(pixels, minScrollExtent) +
         math.min(viewportDimension, maxScrollExtent - minScrollExtent);
}