initial commit

src/world/ElevatorShake.lua

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+-- ShakeElevator (pokered engine/overworld/elevator.asm), run after
+-- DisplayElevatorFloorMenu picks a floor (the elevator map script fires
+-- it via BIT_CUR_MAP_USED_ELEVATOR):
+--
+--   * lead-in: ShakeElevator's two ShakeElevatorRedrawRow calls (each
+--     ends in Delay3) plus its own Delay3 are 9 frames; the SilphCo /
+--     RocketHideout ...ShakeScripts prefix one more Delay3 (12 total)
+--     while Celadon's farjps straight in (9).  The row redraws
+--     themselves are a VRAM patch with no port equivalent -- only their
+--     delays are kept.
+--   * SFX_STOP_ALL_MUSIC: the map theme cuts out for the ride.
+--   * 100 loop iterations, 2 frames each (`ld b, 100` / `ld c, 2` +
+--     DelayFrames): `e ^= $fe` flips e between $01 and $ff, so
+--     hSCY = rest + e alternates -1 / +1 around the resting scroll
+--     (first offset -1), and SFX_COLLISION plays every iteration.
+--   * hSCY restored, SFX_STOP_ALL_MUSIC again, then SFX_SAFARI_ZONE_PA
+--     plays and .musicLoop busy-waits on wChannelSoundIDs+CHAN5 until
+--     it ends.
+--   * UpdateSprites + PlayDefaultMusic: the map theme restarts.
+--
+-- SCY scrolls the BG layer only -- OAM sprites stay put -- so this
+-- state drives ow.bgShakeY, which OverworldState:drawWorld adds to the
+-- tile layers and not to the sprites.  While it sits on the stack the
+-- overworld below neither updates nor takes input, like the original's
+-- blocking loop.
+
+local Sound = require("src.core.Sound")
+
+local ElevatorShake = {}
+ElevatorShake.__index = ElevatorShake
+
+local CYCLES = 100        -- ld b, 100
+local FRAMES_PER_CYCLE = 2 -- ld c, 2 / call DelayFrames
+
+-- opts.preFrames: lead-in delay frames (12 Silph/Rocket, 9 Celadon);
+-- opts.onDone: called once the ride is over (the floor warp)
+function ElevatorShake.new(game, ow, opts)
+  opts = opts or {}
+  return setmetatable({
+    game = game,
+    ow = ow,
+    preFrames = opts.preFrames or 12,
+    onDone = opts.onDone,
+    phase = "pre",
+    frames = 0,
+    offset = 1, -- ld e, $1; the first `xor $fe` flips it to -1
+  }, ElevatorShake)
+end
+
+function ElevatorShake:update()
+  if self.phase == "pre" then
+    if self.frames < self.preFrames then
+      self.frames = self.frames + 1
+      return
+    end
+    -- SFX_STOP_ALL_MUSIC: the theme stops just before the first scroll
+    -- write, in the same frame slice
+    require("src.core.Music").stop()
+    self.phase = "shake"
+    self.frames = 0
+  end
+  if self.phase == "shake" then
+    if self.frames % FRAMES_PER_CYCLE == 0 then
+      -- one .shakeLoop iteration: flip the offset, write the scroll,
+      -- retrigger SFX_COLLISION
+      self.offset = -self.offset
+      self.ow.bgShakeY = self.offset
+      Sound.play(self.game.data, "Collision")
+    end
+    self.frames = self.frames + 1
+    if self.frames >= CYCLES * FRAMES_PER_CYCLE then
+      -- ld a, d / ldh [hSCY], a: back to the resting scroll, then the
+      -- arrival chime
+      self.ow.bgShakeY = 0
+      if Sound.stop then Sound.stop("Collision") end -- SFX_STOP_ALL_MUSIC
+      Sound.play(self.game.data, "Safari_Zone_PA")
+      self.phase = "pa"
+    end
+    return
+  end
+  -- .musicLoop: hold until SFX_SAFARI_ZONE_PA finishes (headless the
+  -- sound never starts, so this resolves on the next frame)
+  if Sound.isPlaying and Sound.isPlaying("Safari_Zone_PA") then return end
+  require("src.core.Music").restoreMap(self.game.data) -- PlayDefaultMusic
+  self.game.stack:pop()
+  if self.onDone then self.onDone() end
+end
+
+-- safety: never leave a scroll offset behind if popped early
+-- (e.g. Game:returnToTitle popping the whole stack)
+function ElevatorShake:exit()
+  if self.ow then self.ow.bgShakeY = 0 end
+end
+
+return ElevatorShake