# draw_order.ludic - painting order, and clipping that nests
function fr_clip_push(ui_st: mut UiState, x: float, y: float, w: float, h: float) -> void {
  var x0 = x
  var y0 = y
  var x1 = x + w
  var y1 = y + h
  let n = len(ui_st.fr_clips)
  if n >= 4 {
    x0 = Math.max(x0, ui_st.fr_clips[n - 4])
    y0 = Math.max(y0, ui_st.fr_clips[n - 3])
    x1 = Math.min(x1, ui_st.fr_clips[n - 2])
    y1 = Math.min(y1, ui_st.fr_clips[n - 1])
  }
  ui_kept(ui_st.fr_clips, x0)
  ui_kept(ui_st.fr_clips, y0)
  ui_kept(ui_st.fr_clips, x1)
  ui_kept(ui_st.fr_clips, y1)
  ui_st.ui_be.clip(x0, y0, Math.max(x1 - x0, 0.0), Math.max(y1 - y0, 0.0))
}
function fr_clip_pop(ui_st: mut UiState) -> void {
  for i in 0 .. 4 {                   # the top rectangle taken off in place
    if len(ui_st.fr_clips) > 0 { List.pop(ui_st.fr_clips) }
  }
  let n = len(ui_st.fr_clips)
  if n >= 4 { ui_st.ui_be.clip(ui_st.fr_clips[n - 4], ui_st.fr_clips[n - 3], ui_st.fr_clips[n - 2] - ui_st.fr_clips[n - 4], ui_st.fr_clips[n - 1] - ui_st.fr_clips[n - 3]) } else if ui_st.ui_be.unclip != null { ui_st.ui_be.unclip() }
}
# the children in painting order: those in the flow first, then positioned ones by z-index
function fr_children(ui_st: mut UiState, n: UiNode) -> void {
  var positioned = 0
  for i in 0 .. len(n.children) {
    if n.children[i].popover { ui_kept(ui_st.pop_list, n.children[i]) } else if n.children[i].pos == 0 { fr_draw(ui_st, n.children[i]) } else { positioned += 1 }
  }
  if positioned == 0 { return }
  var lo = 1000000
  var hi = -1000000
  for i in 0 .. len(n.children) {
    if n.children[i].pos != 0 and not n.children[i].popover {
      lo = Math.min(lo, n.children[i].z)
      hi = Math.max(hi, n.children[i].z)
    }
  }
  for z in lo .. hi + 1 {
    for i in 0 .. len(n.children) {
      if n.children[i].pos != 0 and not n.children[i].popover and n.children[i].z == z { fr_draw(ui_st, n.children[i]) }
    }
  }
}