How to prevent scrolling beyond the last line?

[Denis535]

I am making an extension for smooth scrolling.
But I want my extension to stop scrolling when the last line is already fully visible.
So, how to determine that the last line is completely visible?

if (args.Key is Key.Add) {
    if (!args.IsRepeat) {
        View.DisplayTextLineContainingBufferPosition( new SnapshotPoint( View.TextSnapshot, 0 ), 0, ViewRelativePosition.Top );
        View.ViewportLeft = 0;
        View.Caret.MoveTo( new SnapshotPoint( View.TextSnapshot, 0 ), PositionAffinity.Predecessor );
        View.VisualElement.UpdateLayout();
    } else {
        if (true) { // If the last line is still not visible, then continue scrolling
            var delta = args.KeyboardDevice.IsKeyDown( Key.LeftShift ) ? 8 : 4;
            View.ViewScroller.ScrollViewportVerticallyByPixels( -delta );
            View.VisualElement.UpdateLayout();
        }
    }
    args.Handled = true;
}

[Denis535]

One can compare LastVisibleLine.End.Position and TextSnapshot.Length.

if (view.TextViewLines.LastVisibleLine.End.Position < view.TextSnapshot.Length) {
    // continue scrolling
}