The Face Object Field Actors on scroll event

on-scroll-event is invoked every time the mouse wheel is used over the face to scroll up or down, but not for clicking.

The argument and the return value is the event object.

Do not confuse this with on-scroll which is used to scroll a face using a SCROLLER style.

Examples

Scroll by line or page (BUMP-SCROLL is a function specific to the style this source comes from):

on-scroll-event: [ ; arg: event
  dy: none
  switch arg/type [
    scroll-line [dy: arg/offset/y / -30]
    scroll-page [dy: negate arg/offset/y]
  ]
  if dy [bump-scroll face dy]
  none
]