Port the fishing rods and wild Magikarp

The Old, Good and Super Rods run FishFunction facing water: the map's fish
group and Fish pick no fish, no bite, or a Pokémon from FishGroups and the
time of day's TimeFishGroups. The player casts and jiggles with the
fishing frames drawn from LoadFishingGFX's tiles, shows "!" on a bite, and
the hooked Pokémon attacks as BATTLETYPE_FISH. Facing pieces now use
signed offsets, which the rod above and left of the player needs.

Wild Magikarp no longer stop a battle: LoadEnemyMon redraws their DVs
through CalcMagikarpLength and its filters, as the original does. The
length routine matches the original in the reference emulator.

Part of #27

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/battle.test.ts

@@ -179,7 +179,7 @@ describe.skipIf(!existsSync(romPath))(
     });
 
     it("refuses battles that need untranslated rules", () => {
-      const { battle: game } = battle([starter()], { species: 129, level: 5 });
+      const { battle: game } = battle([starter()], { species: 201, level: 5 });
       expect(() => play(game)).toThrow(UnsupportedBattle);
     });
   },

tests/field-items.test.ts

@@ -13,13 +13,16 @@ import {
 import { StartMenuRun } from "../src/game/scripts/start-menu";
 import { defaultTextContext } from "../src/game/scripts/text";
 import { OVERWORLD } from "../src/game/rom/profile";
-import { close, useItem } from "./menu-driver";
+import { fish } from "../src/game/scripts/fish";
+import { Battle, magikarpLength } from "../src/game/battle/battle";
+import { close, open, pick, pickItem, useItem } from "./menu-driver";
 import { settle } from "./world-driver";
 
 const romPath =
   process.env.CRYSTAL_ROM_PATH ??
   "Pokemon - Crystal Version (UE) (V1.1) [C][!].gbc";
 const PLAYERS_ROOM = "24:7",
+  NEW_BARK_TOWN = "24:4",
   ROUTE_30 = "26:1",
   RADIO_TOWER_3F = "3:19",
   GOLDENROD_UNDERGROUND = "3:53",
@@ -38,7 +41,16 @@ const POTION = 0x12,
   ITEMFINDER = 0x37,
   CARD_KEY = 0x7f,
   BASEMENT_KEY = 0x85,
-  SQUIRTBOTTLE = 0xaf;
+  SQUIRTBOTTLE = 0xaf,
+  OLD_ROD = 0x3a,
+  GOOD_ROD = 0x3b,
+  SUPER_ROD = 0x3d;
+const MAGIKARP = 129,
+  KRABBY = 98,
+  CORSOLA = 222,
+  STARYU = 120;
+const FISHGROUP_SHORE = 1;
+const FACING_FISH_RIGHT = 0x13;
 const SPRITEMOVEDATA_SUDOWOODO = 0x17;
 const OAK_WARNING = "OAK: CHRIS! This isn't the time to use that!";
 
@@ -410,4 +422,190 @@ describe.skipIf(!existsSync(romPath))("field items", () => {
       "CHRIS used the\nSQUIRTBOTTLE.",
     ]);
   });
+
+  it("fishes from FishGroups by rod and time of day", () => {
+    const r = new CrystalAssets(new Uint8Array(readFileSync(romPath))).reader;
+    const cast = (rod: number, time: number, ...draws: number[]) =>
+      fish(r, FISHGROUP_SHORE, rod, time, () => {
+        const draw = draws.shift();
+        if (draw === undefined) throw new Error("No draw left.");
+        return draw;
+      });
+    // A bite below 50 percent + 1 ($80), then the first entry the roll
+    // does not exceed: 70 percent + 1, 85 percent + 1, 100 percent.
+    expect(cast(0, 1, 127, 0)).toEqual({ species: MAGIKARP, level: 10 });
+    expect(cast(0, 1, 128)).toBeUndefined();
+    expect(cast(0, 1, 0, 179)).toEqual({ species: MAGIKARP, level: 10 });
+    expect(cast(0, 1, 0, 255)).toEqual({ species: KRABBY, level: 10 });
+    // The Good Rod's last entry is TimeFishGroups 0: Corsola by day,
+    // Staryu from the night on.
+    expect(cast(1, 0, 0, 255)).toEqual({ species: CORSOLA, level: 20 });
+    expect(cast(1, 1, 0, 255)).toEqual({ species: CORSOLA, level: 20 });
+    expect(cast(1, 2, 0, 255)).toEqual({ species: STARYU, level: 20 });
+    expect(cast(2, 1, 0, 0)).toEqual({ species: KRABBY, level: 40 });
+  });
+
+  it("draws a wild Magikarp's DVs again below four feet, except at the Lake of Rage", () => {
+    const assets = new CrystalAssets(new Uint8Array(readFileSync(romPath)));
+    const id = 0x1234;
+    const feet = (dvs: number) => magikarpLength(assets.reader, dvs, id).feet;
+    // Nonzero, unlike the draws that follow.
+    const short = [...Array(0x10000).keys()].find(
+        (dvs) => dvs > 0x100 && feet(dvs) < 4,
+      )!,
+      long = [...Array(0x10000).keys()].find(
+        (dvs) => dvs > 0x100 && feet(dvs) >= 4,
+      )!;
+    /** The wild Magikarp's DVs for these Random draws (then zeros). */
+    const dvs = (mapId: string, ...draws: number[]) => {
+      const game = new Battle({
+        data: assets.pokemon,
+        party: [
+          generatePartyMon(assets.pokemon, {
+            species: 155,
+            level: 5,
+            item: 0,
+            otId: id,
+            ot: "CHRIS",
+            dvs: 0x823b,
+            caughtData: 0,
+          }),
+        ],
+        playerId: id,
+        playerName: "CHRIS",
+        timeOfDay: 1,
+        pokedex: { seen: new Set(), caught: new Set() },
+        random: () => draws.shift() ?? 0,
+        wild: { species: MAGIKARP, level: 10 },
+        fish: true,
+        mapId,
+        text: () => defaultTextContext("CHRIS"),
+      });
+      const first = game.run().next().value;
+      expect(first && "text" in first && first.text).toBe(
+        "The hooked\nMAGIKARP\nattacked!",
+      );
+      return game.enemy.mon.dvs;
+    };
+    const hi = (value: number) => value >> 8,
+      lo = (value: number) => value & 0xff;
+    // No item (0), the DVs, then 39 percent + 1 (100) skips the floor.
+    expect(dvs(NEW_BARK_TOWN, 0, hi(short), lo(short), 99)).toBe(short);
+    expect(
+      dvs(NEW_BARK_TOWN, 0, hi(short), lo(short), 100, hi(long), lo(long), 100),
+    ).toBe(long);
+    // The Lake of Rage (9:6) skips it without a draw, and so does any map
+    // in group 9 or numbered 6.
+    for (const map of ["9:6", "9:1", "24:6"])
+      expect(dvs(map, 0, hi(short), lo(short), 255)).toBe(short);
+  });
+
+  describe("fishing in New Bark Town", () => {
+    /** Facing the sea, with a rod and a constant random byte. */
+    function shore(random: number, rod = OLD_ROD) {
+      const assets = new CrystalAssets(new Uint8Array(readFileSync(romPath)));
+      const world = new GameWorld(
+        assets,
+        () => new Date("2026-09-22T12:00:00"),
+        () => random,
+      );
+      world.state.party = [
+        generatePartyMon(assets.pokemon, {
+          species: 155,
+          level: 5,
+          item: 0,
+          otId: world.playerId,
+          ot: "CHRIS",
+          dvs: 0x823b,
+          caughtData: 0,
+        }),
+      ];
+      world.state.bag.keyItems = [rod];
+      world.state.scenes[NEW_BARK_TOWN] = 1;
+      world.restore({
+        ...world.save(),
+        map: NEW_BARK_TOWN,
+        x: 17,
+        y: 7,
+        direction: "right",
+        objects: [],
+      });
+      return world;
+    }
+    /** USE from the pack, then tick until a page or a battle appears,
+     * recording the player's facings and emotes meanwhile. */
+    function cast(world: GameWorld, rod = OLD_ROD) {
+      open(world);
+      pick(world, "PACK");
+      pickItem(world, rod);
+      const items =
+        world.dialogue?.choice?.kind === "menu"
+          ? world.dialogue.choice.items
+          : [];
+      world.choose(items.indexOf("USE"));
+      const facings = new Set<number | undefined>(),
+        emotes = new Set<number>();
+      let ticks = 0;
+      for (; ticks < 400 && !world.dialogue && !world.battle; ticks++) {
+        world.tick();
+        facings.add(world.poses().find((pose) => pose.id === 0)?.facing);
+        if (world.emote) emotes.add(world.emote.emote);
+      }
+      return { facings, emotes, ticks };
+    }
+
+    it("hooks a Pokémon that attacks", () => {
+      const world = shore(0);
+      const { facings, emotes } = cast(world);
+      // Cast, four bites with the "!" bubble (EMOTE_SHOCK), then the rod
+      // is pulled in.
+      expect(facings).toContain(FACING_FISH_RIGHT);
+      expect([...emotes]).toEqual([0]);
+      expect(world.dialogue?.pages).toEqual(["Oh!\nA bite!"]);
+      // .Movement_RestoreRod hid the bubble before the text.
+      expect(world.emote).toBeUndefined();
+      expect(world.poses().find((pose) => pose.id === 0)?.facing).toBe(
+        FACING_FISH_RIGHT,
+      );
+      world.advanceDialogue();
+      // PutTheRodAway, then the battle: BATTLETYPE_FISH.
+      for (let tick = 0; tick < 100 && !world.battle?.message; tick++)
+        world.tick();
+      expect(
+        world.poses().find((pose) => pose.id === 0)?.facing,
+      ).toBeUndefined();
+      expect(world.battle?.message?.text).toBe(
+        "The hooked\nMAGIKARP\nattacked!",
+      );
+      expect(world.diagnostic).toBe("");
+    });
+
+    it("gets no bite, or nothing at all where the map has no fish", () => {
+      for (const group of [undefined, 0]) {
+        const world = shore(200, SUPER_ROD);
+        if (group !== undefined) world.map.fishGroup = group;
+        const { facings, emotes } = cast(world, SUPER_ROD);
+        expect(facings).toContain(FACING_FISH_RIGHT);
+        expect(emotes.size).toBe(0);
+        expect(world.dialogue?.pages).toEqual(["Not even a nibble!"]);
+        expect(close(world)).toEqual(["Not even a nibble!"]);
+        expect(
+          world.poses().find((pose) => pose.id === 0)?.facing,
+        ).toBeUndefined();
+        expect(world.battle).toBeUndefined();
+        expect(world.state.bag.keyItems).toEqual([SUPER_ROD]);
+      }
+    });
+
+    it("needs water ahead and no surfing, or Oak objects", () => {
+      const turned = shore(0, GOOD_ROD);
+      turned.restore({ ...turned.save(), direction: "left" });
+      expect(useItem(turned, GOOD_ROD)).toEqual([OAK_WARNING]);
+      close(turned);
+      const surfing = shore(0, GOOD_ROD);
+      surfing.restore({ ...surfing.save(), x: 18, playerState: 4 });
+      expect(useItem(surfing, GOOD_ROD)).toEqual([OAK_WARNING]);
+      close(surfing);
+    });
+  });
 });

tests/foundation-browser.spec.ts

@@ -19,7 +19,8 @@ async function start(
     | "pokegear"
     | "mom"
     | "fly"
-    | "headbutt" = false,
+    | "headbutt"
+    | "fishing" = false,
 ) {
   await page.route("**/src/game/runtime.ts", async (route) => {
     const response = await route.fetch(),
@@ -507,6 +508,32 @@ test("Headbutt shakes a tree and a sleeping Hoothoot falls out", async ({
   await expect(screen).toHaveAttribute("data-map", "24:3");
 });
 
+test("the Old Rod hooks a Magikarp from New Bark Town's shore", async ({
+  page,
+}) => {
+  await start(page, "fishing");
+  const text = page.locator("#dialogue-text"),
+    choices = page.locator("#dialogue-choice"),
+    pack = page.locator("#mart");
+  await page.keyboard.press("Enter");
+  await choices.getByRole("option", { name: /^PACK/ }).click();
+  await page.keyboard.press("ArrowRight");
+  await page.keyboard.press("ArrowRight");
+  await pack.getByRole("button", { name: "OLD ROD", exact: true }).click();
+  await choices.getByRole("option", { name: "USE", exact: true }).click();
+  // The cast, 40 frames, four bites with "!", 40 more frames.
+  await page.clock.runFor(5_000);
+  await expect(text).toHaveText(/Oh!\s+A bite!/);
+  await page.keyboard.press("KeyX");
+  await page.clock.runFor(5_000);
+  await expect(page.locator("#battle")).toBeVisible();
+  await expect(page.locator("#battle-text")).toHaveText(
+    /The hooked\s+MAGIKARP\s+attacked!/,
+  );
+  await expect(page.locator("#battle-foe-name")).toHaveText("MAGIKARP");
+  await expect(page.locator("#game-notice")).toHaveText("");
+});
+
 test("Mom keeps the player's money with the digit box", async ({ page }) => {
   await start(page, "mom");
   const text = page.locator("#dialogue-text"),

tests/foundation-fixture.ts

@@ -12,7 +12,8 @@ import { generatePartyMon } from "../src/game/party/pokemon";
  * the Storm Badge, and New Bark Town and Cherrygrove City visited.
  * "headbutt" faces Route 29's first reachable Headbutt tree from below
  * with a Pokémon that knows Headbutt; Random always returning 0 drops a
- * sleeping Hoothoot. */
+ * sleeping Hoothoot. "fishing" faces the sea on New Bark Town's shore
+ * with the Old Rod, which then hooks a Magikarp. */
 export function foundationFixture(
   assets: CrystalAssets,
   room:
@@ -23,7 +24,8 @@ export function foundationFixture(
     | "pokegear"
     | "mom"
     | "fly"
-    | "headbutt",
+    | "headbutt"
+    | "fishing",
 ) {
   const world = new GameWorld(
     assets,
@@ -45,7 +47,8 @@ export function foundationFixture(
       }),
     );
     world.state.bag.items = [{ item: 18, quantity: 5 }]; // POTION
-    if (room === "candy") world.state.bag.items.push({ item: 0x20, quantity: 1 });
+    if (room === "candy")
+      world.state.bag.items.push({ item: 0x20, quantity: 1 });
   }
   if (room === "pokegear" || room === "mom") {
     world.state.party = [
@@ -80,10 +83,26 @@ export function foundationFixture(
     mon.pp = [15, 0, 0, 0];
     world.state.party = [mon];
     world.state.flags.add(OW.ENGINE_STORMBADGE);
-    for (const spawn of [14, 15]) // SPAWN_NEW_BARK, SPAWN_CHERRYGROVE
+    for (const spawn of [14, 15])
+      // SPAWN_NEW_BARK, SPAWN_CHERRYGROVE
       world.state.flags.add(assets.spawnEngineFlag(spawn)!);
     for (let event = 0; event < 8; event++) world.state.events.delete(event);
   }
+  if (room === "fishing") {
+    world.state.party = [
+      generatePartyMon(assets.pokemon, {
+        species: 155,
+        level: 8,
+        item: 0,
+        otId: world.playerId,
+        ot: "CHRIS",
+        dvs: 0x9abc,
+        caughtData: 0,
+      }),
+    ];
+    world.state.bag.keyItems.push(0x3a); // OLD_ROD
+    for (let event = 0; event < 8; event++) world.state.events.delete(event);
+  }
   if (room === "headbutt") {
     const mon = generatePartyMon(assets.pokemon, {
       species: 158, // TOTODILE
@@ -111,21 +130,26 @@ export function foundationFixture(
   const [map, x, y] =
     room === "headbutt"
       ? headbuttSpot(assets)
-      : room === "center" || room === "candy"
-        ? ["26:5", 9, 2]
-        : room === "poster"
-          ? ["24:7", 6, 1]
-          : room === "mom"
-            ? ["24:6", 7, 3]
-            : room && room !== "pokegear" && room !== "fly"
-              ? ["24:7", 2, 2]
-              : ["24:4", 9, 6];
+      : room === "fishing"
+        ? ["24:4", 17, 7]
+        : room === "center" || room === "candy"
+          ? ["26:5", 9, 2]
+          : room === "poster"
+            ? ["24:7", 6, 1]
+            : room === "mom"
+              ? ["24:6", 7, 3]
+              : room &&
+                  room !== "pokegear" &&
+                  room !== "fly" &&
+                  room !== "fishing"
+                ? ["24:7", 2, 2]
+                : ["24:4", 9, 6];
   world.restore({
     ...save,
     map,
     x,
     y,
-    direction: room === "mom" ? "down" : "up",
+    direction: room === "mom" ? "down" : room === "fishing" ? "right" : "up",
     objects: [],
   });
   return world;

tests/movement-fixture.ts

@@ -28,6 +28,7 @@ export class MovementAssets extends CrystalAssets {
         environment: 1,
         paletteMode: 1,
         phoneService: 0,
+        fishGroup: 0,
         blocks: new Uint8Array(16),
         warps: [],
         backgroundEvents: [],

tests/reference-parity.spec.ts

@@ -6,6 +6,7 @@ import {
   Battle,
   applyTypeMatchups,
   calculateDamage,
+  magikarpLength,
   restoreHealth,
   restoredPP,
   sendOutText,
@@ -638,3 +639,75 @@ test("native switch texts, healing, PP, happiness and CalcPlayerStats match the
     ).toEqual(results.stats[index]);
   });
 });
+
+test("native Magikarp lengths match CalcMagikarpLength", async ({ page }) => {
+  test.skip(
+    !existsSync(romPath) || !existsSync(symbolsPath),
+    "Requires the local user ROM and the private PRET rebuild.",
+  );
+  const { at, routine } = loadSymbols();
+  const reader = new CrystalAssets(new Uint8Array(readFileSync(romPath))).reader;
+  let seed = 0x4a39;
+  const next = (limit: number) => {
+    seed = (seed * 1103515245 + 12345) >>> 0;
+    return (seed >>> 8) % limit;
+  };
+  // Random DVs and IDs, plus indexes below 10 and at the table's edges.
+  const cases = [
+    ...Array.from({ length: 1500 }, () => ({ dvs: next(0x10000), id: next(0x10000) })),
+    ...[0x0000, 0x0009, 0x000a, 0x00ff, 0x0100, 0xfdff, 0xfe00, 0xff00, 0xffff].map((dvs) => ({
+      dvs,
+      id: 0,
+    })),
+  ];
+  await openReference(page);
+  const addresses = {
+    calc: routine("CalcMagikarpLength"),
+    length: at("wMagikarpLength"),
+  };
+  const results = await page.evaluate(
+    async ({ addresses, cases }) => {
+      const { BinjgbEmulator } = await import("/src/emulator/binjgb.ts");
+      const file = (document.querySelector("#reference-fixture") as HTMLInputElement).files![0];
+      const reference = new BinjgbEmulator();
+      await reference.load(new Uint8Array(await file.arrayBuffer()), document.createElement("canvas"));
+      const write = (address: number, value: number) => reference.writeMemory(address, value & 0xff);
+      // Trampoline: DI; SP=$c7fe; switch to the routine's bank; set BC (the
+      // ID) and DE (the DVs); CALL CalcMagikarpLength; write a sentinel; loop.
+      const dvs = 0xc100,
+        id = 0xc102;
+      const program = [
+        0xf3, 0x31, 0xfe, 0xc7, 0x3e, addresses.calc.bank, 0xe0, 0x9d, 0xea, 0x00, 0x20,
+        0x01, id & 0xff, id >> 8, 0x11, dvs & 0xff, dvs >> 8,
+        0xcd, addresses.calc.address & 0xff, addresses.calc.address >> 8,
+        0x3e, 0x42, 0xea, 0xff, 0xc6, 0x18, 0xfe,
+      ];
+      write(0xff70, 1);
+      const lengths = cases.map((input) => {
+        write(dvs, input.dvs >> 8);
+        write(dvs + 1, input.dvs);
+        write(id, input.id >> 8);
+        write(id + 1, input.id);
+        write(0xc6ff, 0);
+        program.forEach((value, index) => write(0xc000 + index, value));
+        reference.setProgramCounter(0xc000);
+        reference.advanceFrames(2);
+        return {
+          returned: reference.readMemory(0xc6ff) === 0x42,
+          feet: reference.readMemory(addresses.length),
+          inches: reference.readMemory(addresses.length + 1),
+        };
+      });
+      reference.dispose();
+      return lengths;
+    },
+    { addresses, cases },
+  );
+  cases.forEach((input, index) => {
+    const { returned, ...original } = results[index];
+    expect(returned, `case ${index} returned`).toBe(true);
+    expect(magikarpLength(reader, input.dvs, input.id), JSON.stringify(input)).toEqual(original);
+  });
+  const lengths = new Set(results.map(({ feet, inches }) => feet * 12 + inches));
+  expect(lengths.size).toBeGreaterThan(30);
+});

tests/start-menu.test.ts

@@ -20,7 +20,6 @@ const BICYCLE = 7,
   ANTIDOTE = 9,
   FULL_RESTORE = 0x0e,
   POTION = 0x12,
-  OLD_ROD = 0x3a,
   THUNDERSTONE = 0x17,
   HP_UP = 0x1a,
   RARE_CANDY = 0x20,
@@ -625,10 +624,8 @@ describe.skipIf(!existsSync(romPath))("the start menu", () => {
     expect(world.state.registeredItem).toEqual({ which: 0, item: 0 });
   });
 
-  it("offers no USE without a field menu, and a notice for unported effects", () => {
+  it("offers no USE without a field menu", () => {
     const world = fixture();
-    world.state.bag.items.push({ item: BERRY, quantity: 1 });
-    world.state.bag.keyItems.push(OLD_ROD);
     world.state.bag.balls = [{ item: 5, quantity: 3 }];
     open(world);
     pick(world, "PACK");
@@ -636,11 +633,7 @@ describe.skipIf(!existsSync(romPath))("the start menu", () => {
     pickItem(world, 5);
     expect(menuItems(world)).toEqual(["GIVE", "TOSS", "QUIT"]);
     pick(world, "QUIT");
-    pickItem(world, OLD_ROD);
-    pick(world, "USE");
-    expect(world.notice).toBe("Using OLD ROD is not ported yet.");
     close(world);
-    expect(world.state.bag.keyItems).toContain(OLD_ROD);
   });
 
   it("raises a level with a Rare Candy, forgetting a move to learn a new one", () => {