Mouse events for anywhere on the window. Mouse events for right scrollbar button. Unhide the un-pressed button layer. Mouse events for left scrollbar button. Unhide the un-pressed button layer.
Mouse events for up scrollbar button.
Unhide the un-pressed button layer. Mouse events for down scrollbar button. Unhide the un-pressed button layer. Mouse events for horizontal scrollbar stub. If we are, calculate the new position, and update the clip.