ludic/runtime/native/input.ludic

# ============================================================================
# input.ludic — action maps + deterministic input recording/replay (#7).
#
# The raw platform gives one key per frame (Input.key / rt_poll). This layer
# adds the two ideas the input proposal leads with:
#
#   * Action maps — gameplay reads *named actions*, not physical keys, so a key
#     is rebindable at runtime and a scheme is data. Bind with Input.bind, read
#     with Input.down / Input.pressed, remap with Input.rebind.
#   * Deterministic record/replay — because the sim is deterministic in its input
#     stream, snapshotting the per-frame key and feeding it back reproduces a run
#     exactly (free replays, the seed of lockstep netcode). Input.poll is the one
#     call that advances a frame of input; it reads the live key, records it, or
#     replays a recorded one depending on the mode — "read input" and "read a
#     recorded snapshot" are the same call, as the proposal asks.
#
# All integer and deterministic. The device layer the proposal also sketches —
# multiple simultaneous keys, gamepads, touch, analog axes/vectors — needs a
# platform key-state backend and is tracked separately; this layer stands on the
# single-key poll every target already provides.
# ============================================================================

const INPUT_MAX_ACT:  int = 32     # named actions
const INPUT_MAX_KEYS: int = 4      # physical keys bound per action
const INPUT_REC_CAP:  int = 8192   # recordable frames

var input_names: pointers = null   # action name per slot (0..input_nact)
var input_keys:  words = null      # INPUT_MAX_ACT * INPUT_MAX_KEYS key codes (0 = empty)
var input_nact:  int   = 0

var input_frame: int = 0           # the key polled this frame
var input_last:  int = 0           # the key polled last frame (for edges)

var input_mode:  int   = 0         # 0 = live, 1 = record, 2 = replay
var input_rec:   words = null      # recorded key per frame
var input_recn:  int   = 0         # frames recorded
var input_pos:   int   = 0         # replay / record cursor

function input_init() -> void {
  if input_names == null {
    input_names = bytes(INPUT_MAX_ACT * 8)           # a pointer (8 bytes) per action slot
    input_keys  = words(INPUT_MAX_ACT * INPUT_MAX_KEYS)
  }
}

# slot of the action `name`, or -1. Names compare by byte-string equality.
function input_find(name: pointer) -> int {
  input_init()
  var i = 0
  while i < input_nact {
    if input_names[i] == name { return i }
    i = i + 1
  }
  return 0 - 1
}

# get-or-create the slot for `name`.
function input_slot(name: pointer) -> int {
  let f = input_find(name)
  if f >= 0 { return f }
  if input_nact >= INPUT_MAX_ACT { return INPUT_MAX_ACT - 1 }   # silently reuse the last slot when full
  let s = input_nact
  input_names[s] = name
  input_nact = input_nact + 1
  return s
}

# bind physical `key` to the named action, creating the action if new. A key
# already bound to the action is left as-is (idempotent).
function input_bind(name: pointer, key: int) -> void {
  let s = input_slot(name)
  let base = s * INPUT_MAX_KEYS
  var i = 0
  while i < INPUT_MAX_KEYS {
    if input_keys[base + i] == key { return }        # already bound
    i = i + 1
  }
  i = 0
  while i < INPUT_MAX_KEYS {
    if input_keys[base + i] == 0 { input_keys[base + i] = key;  return }
    i = i + 1
  }
}

# runtime rebinding: replace `oldkey` with `newkey` on the named action. A no-op
# if the action or the old key is not found.
function input_rebind(name: pointer, oldkey: int, newkey: int) -> void {
  let s = input_find(name)
  if s < 0 { return }
  let base = s * INPUT_MAX_KEYS
  var i = 0
  while i < INPUT_MAX_KEYS {
    if input_keys[base + i] == oldkey { input_keys[base + i] = newkey;  return }
    i = i + 1
  }
}

# does key `k` (0 = none) fire the action in slot `s`?
function input_slot_has(s: int, k: int) -> bool {
  if s < 0 { return false }
  if k == 0 { return false }
  let base = s * INPUT_MAX_KEYS
  var i = 0
  while i < INPUT_MAX_KEYS {
    if input_keys[base + i] == k { return true }
    i = i + 1
  }
  return false
}

# Advance one frame of input and return the frame's key. This is the single
# per-frame input read: call it once at the top of a frame.
#   live   — read the live key (rt_poll).
#   record — read the live key and append it to the recording.
#   replay — take the next key from the recording (the live device is ignored).
function input_poll() -> int {
  input_last = input_frame
  if input_mode == 2 {                               # replay
    if input_pos < input_recn { input_frame = input_rec[input_pos];  input_pos = input_pos + 1 }
    else { input_frame = 0 }                          # past the end of the tape: no input
    return input_frame
  }
  let k = rt_poll()
  if input_mode == 1 {                               # record
    if input_rec == null { input_rec = words(INPUT_REC_CAP) }
    if input_recn < INPUT_REC_CAP { input_rec[input_recn] = k;  input_recn = input_recn + 1 }
  }
  input_frame = k
  return k
}

# is the named action held on the frame last polled?
function input_down(name: pointer) -> bool {
  return input_slot_has(input_find(name), input_frame)
}

# did the named action go down this frame (down now, not down last frame)?
function input_pressed(name: pointer) -> bool {
  let s = input_find(name)
  return input_slot_has(s, input_frame) and (not input_slot_has(s, input_last))
}

# begin recording polled input from the next frame (resets the tape).
function input_record() -> void {
  if input_rec == null { input_rec = words(INPUT_REC_CAP) }
  input_recn = 0
  input_pos = 0
  input_mode = 1
}

# replay the recording from its start; subsequent Input.poll calls read the tape.
function input_replay() -> void {
  input_pos = 0
  input_mode = 2
}