# scroll_held.ludic - a scroll box held at an offset: scroll-top="{px}" puts it there every frame
# (the wheel, the bar and the focus still move it, and say so with on-scroll and event.value, for
# the program to keep or not), and ui_scroll_set(id or key, px) moves it once
export function ui_scroll_set(ui_st: mut UiState, key: string, px: float) -> void {
  push(ui_st.sc_want_keys, key)
  push(ui_st.sc_want_px, px)
}
# how far a box is scrolled before this frame's input: what it was, what ui_scroll_set asked for,
# or what its scroll-top says
function sc_held(ui_st: mut UiState, n: UiNode, off: float, live: bool) -> float {
  var at = off
  if live {
    let keys = ui_st.sc_want_keys          # the asks for this box taken out in place, the others kept
    let pxs = ui_st.sc_want_px
    var kept = 0
    for i in 0 .. len(keys) {
      if keys[i] == n.key or (n.id != "" and keys[i] == n.id) { at = ui_px(ui_st, pxs[i]) } else {
        keys[kept] = keys[i]
        pxs[kept] = pxs[i]
        kept += 1
      }
    }
    while len(keys) > kept {
      List.pop(keys)
      List.pop(pxs)
    }
  }
  if ui_attr_has(n, "scroll-top") {
    let v = ui_attr(n, "scroll-top")
    if Value.kind(v) != 0 { at = ui_px(ui_st, el_numv(ui_st, v)) }
  }
  return at
}