# frame.ludic - a screen shown: built from the view's model, laid out, drawn, and its presses
# run once the frame is drawn, so nothing the view does can change a frame half way through it;
# the actions they dispatch are reduced before ui_show returns, so the frame presented next is built
# from what they changed

export function ui_show(ui_st: mut UiState, screen: string, view: UiView, x: float, y: float, w: float, h: float) -> void {
  in_read(ui_st)
  dv_before(ui_st)
  ui_st.an_frame += 1
  ui_viewport(ui_st, w, h)
  let root = ui_nodes(ui_st, screen, view)
  if root == null { return }
  ui_place(ui_st, root, x, y, w, h)
  nt_fired_clear(ui_st)
  sc_undo(root)
  sc_update(ui_st, root)
  fr_pointer(ui_st, root)
  fc_keys(ui_st, root)
  hd_tick(ui_st, root)
  tt_track(ui_st, root, ui_st.in_now.x, ui_st.in_now.y)
  fb_keep(ui_st, screen, root)
  if ui_st.ui_be != null and ui_st.ui_be.text != null {
    fr_draw(ui_st, root)
    pp_draw_top(ui_st)
    tt_draw(ui_st, root)
  }
  dv_after(ui_st, screen, root)
  lc_run(ui_st, screen)
  nt_fired_run(ui_st)
  drain_actions()                                # 0.R4: what the presses dispatched is reduced before the host presents
}
# the screen's nodes for this frame, not yet laid out - for a test, or a host that places them
export function ui_nodes(ui_st: mut UiState, screen: string, view: UiView) -> UiNode {
  let si = lib_find(ui_st.lib_screen_names, screen)
  let cls = uc_find(ui_st, screen)
  if si < 0 and cls != null { return fr_class_nodes(ui_st, cls) }
  if si < 0 {
    @alloc_ok("only when a template is wrong: a broken screen, never a working one")
    ui_err(ui_st, `there is no screen {screen} - ui_load the file that has it`)
    return null
  }
  let t = ui_st.lib_screens[si]
  pl_begin(ui_st, screen)
  ui_st.uv_on = true
  lc_begin(ui_st)
  ui_st.ui_view = view
  let e = env_new(ui_st, null)
  if view != null and view.model != null { e.model = view.model() } else { e.model = Value.object() }
  e.state = st_for(ui_st, screen, t, e)
  let root = nd_take(ui_st)
  root.key = screen
  root.env = e
  root.sheet = t.sheet
  root.tag = "screen"
  for i in 0 .. len(t.keys) {
    if t.keys[i] != "name" { el_keep(ui_st, root, t.keys[i], ui_eval(ui_st, t.vals[i], e)) }
  }
  bd_kids(ui_st, t.kids, e, screen, root.children)
  cs_tree(ui_st, root)
  ui_st.uv_on = false
  return root
}
# the room vw, vh and @media measure against; ui_show sets it to the screen's rectangle
export function ui_viewport(ui_st: mut UiState, w: float, h: float) -> void {
  ui_st.ly_vp_w = w
  ui_st.ly_vp_h = h
}
export function ui_place(ui_st: mut UiState, root: UiNode, x: float, y: float, w: float, h: float) -> void {
  ui_st.ly_vp_x = x
  ui_st.ly_vp_y = y
  root.w = UI_FILL
  root.h = UI_FILL
  let fg = 15658734
  ui_st.ly_fg_a = 1.0
  ly_measure(ui_st, root, w, ui_px(ui_st, 16.0), fg)
  ly_place(ui_st, root, x, y, w, h)
  sc_apply(ui_st, root)
  pp_anchor_all(ui_st, root)
}
# a press, as if the pointer had made it
export function ui_press(ui_st: mut UiState, n: UiNode) -> void {
  if n.act != null and n.enabled { act_run(ui_st, n.act, n.env) }
  drain_actions()
}
# any event, as if the element had fired it - for a test
export function ui_event(ui_st: mut UiState, n: UiNode, name: string, value: Val) -> void { nt_run(ui_st, n, name, value) }