fix(gen2): honor battle party grid navigation

docs/mod-api-gen2-compat.md

@@ -512,8 +512,9 @@ gains a field instead of the name gaining a prefix.
   id under Gen 1's `name` key, which is the one payload difference the
   numeric flag space forces.
 - *Menus (`src/ui/gen2/`):* `ui.start_menu.items`, `ui.title_menu.items`,
-  `ui.options.rows`, `ui.party.submenu`, `ui.naming.grid`, `ui.pc.items`,
-  `ui.list_menu`, `transition.style`. `ui.list_menu` covers Gold's script
+  `ui.options.rows`, `ui.party.submenu`, `ui.party.grid_navigation`,
+  `ui.naming.grid`, `ui.pc.items`, `ui.list_menu`, `transition.style`.
+  `ui.list_menu` covers Gold's script
   menus (`ScriptMenu.lua`); the `Chrome.List` widget the START and title
   menus draw with does not raise it yet, so those two are composed through
   their own hooks only.

src/ui/gen2/BattleState.lua

@@ -2290,6 +2290,7 @@ function BattleState:openParty(forced)
     -- :2702; engine/pokemon/party_menu.asm:660-679).  Only the voluntary list
     -- carries BattleMonMenu; PickPartyMonInBattle has no submenu.
     prompt = forced and "which" or "choose",
+    battle = true,
     battleSubmenu = not forced,
     onCancel = function()
       stack:pop()
@@ -2762,6 +2763,7 @@ function BattleState:openShiftParty()
   self.phase = "submenu"
   Screens.push(self.game, "Gen2PartyMenu", {
     prompt = "which",
+    battle = true,
     onCancel = function()
       stack:pop()
       self.phase = "resolving"
@@ -3135,6 +3137,7 @@ function BattleState:useOnPartyMon(itemId, action)
   self.phase = "submenu"
   Screens.push(self.game, "Gen2PartyMenu", {
     prompt = "useItem",
+    battle = true,
     party = self.battle.party or (self.save and self.save.party),
     onCancel = function()
       stack:pop()

src/ui/gen2/PartyMenu.lua

@@ -76,6 +76,23 @@ local BATTLE_SUBMENU_LEFT, BATTLE_SUBMENU_TOP = 11, 11
 
 -- HP bar is 6 tiles wide (48px) in the party list.
 
+local function gridIndex(index, count, direction)
+  if count < 1 then return nil end
+  local row, col = math.floor((index - 1) / 2), (index - 1) % 2
+  if direction == "left" or direction == "right" then
+    local other = row * 2 + (1 - col) + 1
+    return other <= count and other or index
+  end
+  local step = direction == "up" and -1 or direction == "down" and 1
+  if not step then return nil end
+  local rows = math.ceil(count / 2)
+  for offset = 1, rows do
+    local other = ((row + step * offset) % rows) * 2 + col + 1
+    if other <= count then return other end
+  end
+  return index
+end
+
 function PartyMenu:wantsFillScale() return true end
 function PartyMenu:drawsWidescreen() return true end
 
@@ -114,6 +131,7 @@ function PartyMenu.new(game, opts)
   self.wantsSubmenu = opts.submenu == true
   -- BattleMenu_PKMN's `callfar BattleMonMenu` (engine/battle/core.asm:4810).
   self.wantsBattleSubmenu = opts.battleSubmenu == true
+  self.battle = opts.battle == true
   self.submenu = nil
   -- The held slot while SwitchPartyMons' second pick is open; nil otherwise.
   self.switchFrom = nil
@@ -146,6 +164,13 @@ function PartyMenu:isCancel()
   return self.index > #self.party
 end
 
+function PartyMenu:gridNavigation()
+  if not self.battle
+      or not Runtime.wantsHook("ui.party.grid_navigation") then return false end
+  return Runtime.call("ui.party.grid_navigation", function() return false end,
+                      self) == true
+end
+
 -- ------------------------------------------------------------- mon submenu
 
 -- GetMonSubmenuItems, in its own order: every field move the mon knows first,
@@ -477,7 +502,18 @@ function PartyMenu:update(_dt)
     return
   end
   local total = self:count()
-  if input:wasPressed("up") then
+  local grid
+  if self:gridNavigation() then
+    local direction = input:wasPressed("left") and "left"
+      or input:wasPressed("right") and "right"
+      or input:wasPressed("up") and "up"
+      or input:wasPressed("down") and "down"
+    grid = gridIndex(self.index, #self.party, direction)
+  end
+  if grid then
+    self.index = grid
+    self:storeCursor()
+  elseif input:wasPressed("up") then
     self.index = self.index > 1 and self.index - 1 or total
   elseif input:wasPressed("down") then
     self.index = self.index < total and self.index + 1 or 1

tests/engine/gate_gen2_mod_api.lua

@@ -397,7 +397,8 @@ local GEN2_HOOKS = {
   "world.tod", "map.palette", "fieldmove.eligibility",
   -- menus and the battle intro
   "ui.start_menu.items", "ui.title_menu.items", "ui.options.rows",
-  "ui.party.submenu", "ui.naming.grid", "ui.pc.items", "ui.list_menu",
+  "ui.party.submenu", "ui.party.grid_navigation", "ui.naming.grid",
+  "ui.pc.items", "ui.list_menu",
   "transition.style",
   -- battle
   "battle.damage", "battle.crit", "battle.accuracy", "battle.turn_order",

tests/mod_qol_hooks_tests.lua

@@ -14,6 +14,7 @@ local NamingScreen = require("src.ui.NamingScreen")
 local TextBox = require("src.render.TextBox")
 local ChoiceBox = require("src.ui.ChoiceBox")
 local PartyMenu = require("src.ui.PartyMenu")
+local Gen2PartyMenu = require("src.ui.gen2.PartyMenu")
 local Player = require("src.world.Player")
 local Music = require("src.core.Music")
 
@@ -295,6 +296,16 @@ do
   menu:update(0)
   check(menu.index == 4,
     "removing the hook restores native list navigation immediately")
+
+  local gold = Gen2PartyMenu.new(game, { battle = true })
+  unsub = wrap("ui.party.grid_navigation", function() return true end)
+  gold:update(0)
+  check(gold.index == 3,
+    "a Gold battle party can follow the same companion grid")
+  unsub()
+  gold:update(0)
+  check(gold.index == 4,
+    "Gold restores native party list navigation without the hook")
 end
 
 -- ------- music.volume (distance / indoor muffling)