sacred_k/src/mods/itemstack.cpp

// Item stacks: potions and combat-art runes (requests 2026-10-17,
// docs/item-stacks.md).
//
// Items of the same type that the game counts as consumable (potions, runes;
// ItemIsConsumable 0x43f5f0) share one inventory cell, up to kMaxStack. Such
// items differ only in their object state (measured for runes), so the type
// alone decides. A stack is the one object in the cell plus a count kept here
// (by item id, with the item type to tell a reused id apart) and saved with
// the JSON inventories (src/mods/inventory_save.cpp).
//
// Stacks exist in the players' inventories and the chest (inventory 0x11);
// trader stock waits for stack prices.
//
// - Entry: an item placed into a grid (picked up, bought, dropped from the
//   cursor; cInventoryEntry::PlaceItem 0x5d9ec0) pours into other
//   stacks of its type that have room, on the next engine tick (the caller
//   still uses the object while placing it). An emptied object is removed and
//   destroyed.
// - Sort button (cInventoryEntry::Sort 0x5db670, the inventory window's
//   button): all items of a type are poured together first.
// - Use (cCreature::UseItem 0x54a8f0, measured for potions; runes, class 0x1c,
//   take the same path): the item's event handler (vf18) applies the effect
//   and marks it used up; UseItem then removes it from the grid (RemoveItem
//   0x5da5f0) and destroys it (cObjectManager::DestroyObject 0x5fbe10), and
//   cEngine::UseActionSlot removes it once more. For a stack of more than
//   one, the first removal takes one off the count instead, and the rest of
//   that use leaves the object alone.
// - Load: cInventoryEntry::ReplaceItemId (0x5d80e0, hooked in skillslots.cpp;
//   hero files map saved ids to the new objects) moves the count to the new id.
// - Drawing: the count on each stack's cell, after cInventoryEntry::DrawItems
//   (0x5dc3f0; cell rects from CellRect 0x5dd530).

#include "mods/itemstack.h"
#include "mods/teleportpotion.h"

#include <windows.h>

#include <cwchar>
#include <mutex>
#include <unordered_map>
#include <vector>

#include "game/engine/events.h"
#include "game/engine/items.h"
#include "game/engine/objects.h"
#include "game/ui/text.h"
#include "re/hook.h"

namespace mods::itemstack {
namespace {

constexpr unsigned kMaxStack = 20;

constexpr uint16_t kCountFont = 1;  // as the potion slot counts (potioncounts.cpp)
constexpr uint32_t kCountColor = 0xffffffff;
constexpr int kCountInset = 2;

// How long a drink's later removals of its stack are ignored.
constexpr DWORD kDrinkMs = 100;

struct Stack {
    unsigned count;
    uint32_t type;  // 0: not known yet (set on load before the objects exist)
};

std::mutex g_lock;
std::unordered_map<uint32_t, Stack> g_stacks;

// Stackable items placed into a grid, poured on the next tick.
struct Entry {
    uint8_t* inventory;
    uint32_t id;
};
std::vector<Entry> g_entered;
// Inside cInventoryEntry::Sort (its re-placements are no entries).
thread_local bool g_sorting = false;
// The stack a use just took one from (per thread: uses come from the
// engine and the UI thread).
thread_local uint32_t g_drunk = 0;
thread_local DWORD g_drunkAt = 0;

uint32_t TypeOf(uint32_t id) {
    const void* item = id ? game::GetObjectById(id) : nullptr;
    return item ? game::ItemType(item) : 0;
}

// Stacks exist in the players' inventories and the chest; trader stock not
// yet (buying from a stack would sell the whole stack for one price).
bool Stacks(const void* inventory) {
    return inventory && game::IsPlayerInventory(static_cast<const uint8_t*>(inventory));
}

bool Stackable(uint32_t type) {
    return type && game::ItemIsConsumable(type);
}

bool StackableItem(uint32_t id) {
    return Stackable(TypeOf(id));
}

bool InGrid(const uint8_t* inventory, uint32_t id) {
    bool found = false;
    game::ForEachGridItem(inventory, [&](uint32_t item) { found = found || item == id; });
    return found;
}

// Moves the items of `id` into the other stacks of its type in `inventory`
// that have room (in grid order); an emptied `id` is removed and destroyed.
void Pour(uint8_t* inventory, uint32_t id) {
    const uint32_t type = TypeOf(id);
    if (!Stackable(type)) {
        return;
    }
    const unsigned had = StackCount(id);
    unsigned left = had;
    game::ForEachGridItem(inventory, [&](uint32_t other) {
        if (left == 0 || other == id || TypeOf(other) != type) {
            return;
        }
        const unsigned count = StackCount(other);
        const unsigned room = count < kMaxStack ? kMaxStack - count : 0;
        const unsigned moved = left < room ? left : room;
        if (moved) {
            SetStackCount(other, count + moved);
            left -= moved;
        }
    });
    if (left == had) {
        return;
    }
    if (left > 0) {
        SetStackCount(id, left);
        return;
    }
    using RemoveItemFn = int(__fastcall*)(void*, void*, uint32_t, uint32_t);
    reinterpret_cast<RemoveItemFn>(0x005da5f0)(inventory, nullptr, id, 1);  // cInventoryEntry::RemoveItem
    game::DestroyObject(id);
}

// Pours the stacks from the back of the grid into those before them: full
// stacks first.
void StackAll(uint8_t* inventory) {
    std::vector<uint32_t> items;
    game::ForEachGridItem(inventory, [&](uint32_t id) {
        if (StackableItem(id)) {
            items.push_back(id);
        }
    });
    for (size_t i = items.size(); i-- > 0;) {
        Pour(inventory, items[i]);
    }
}

void OnTick(uint8_t*) {
    std::vector<Entry> entered;
    {
        std::lock_guard guard(g_lock);
        entered.swap(g_entered);
    }
    for (const Entry& entry : entered) {
        if (InGrid(entry.inventory, entry.id)) {
            Pour(entry.inventory, entry.id);
        }
    }
}

struct Registration {
    Registration() { game::OnEngineTick(&OnTick); }
} g_registration;

void DrawCounts(void* inventory, void* renderer) {
    auto* grid = static_cast<const uint8_t*>(inventory);
    const int lineHeight = game::FontLineHeight(kCountFont);
    const unsigned cells = game::GridCells(grid);
    for (unsigned cell = 0; cell < cells; ++cell) {
        const unsigned count = StackCount(game::GridItem(grid, cell));
        if (count <= 1) {
            continue;
        }
        using CellRectFn = game::UiRect*(__fastcall*)(void*, void*, game::UiRect*, uint32_t);
        game::UiRect rect = {};
        reinterpret_cast<CellRectFn>(0x005dd530)(inventory, nullptr, &rect, cell);  // cInventoryEntry::CellRect
        rect.y += rect.h - lineHeight - kCountInset;
        rect.w = static_cast<int16_t>(rect.w - kCountInset);
        wchar_t text[8];
        swprintf_s(text, L"%u", count);
        game::DrawText(renderer, kCountFont, rect, text, kCountColor, game::kTextRight);
    }
}

bool DrinkInProgress(uint32_t id) {
    return id && id == g_drunk && GetTickCount() - g_drunkAt < kDrinkMs;
}

void Forget(uint32_t id) {
    std::lock_guard guard(g_lock);
    g_stacks.erase(id);
}

} // namespace

unsigned StackCount(uint32_t id) {
    if (!id) {
        return 1;
    }
    Stack stack;
    {
        std::lock_guard guard(g_lock);
        const auto it = g_stacks.find(id);
        if (it == g_stacks.end()) {
            return 1;
        }
        stack = it->second;
    }
    const uint32_t type = TypeOf(id);
    if (stack.type == 0 && type != 0) {
        std::lock_guard guard(g_lock);
        g_stacks[id].type = type;  // first seen after loading
        return stack.count;
    }
    return type == stack.type ? stack.count : 1;
}

void SetStackCount(uint32_t id, unsigned count) {
    if (count <= 1) {
        Forget(id);
        return;
    }
    const uint32_t type = TypeOf(id);
    std::lock_guard guard(g_lock);
    g_stacks[id] = {count, type};
}

void OnItemIdReplaced(uint32_t oldId, uint32_t newId) {
    std::lock_guard guard(g_lock);
    const auto it = g_stacks.find(oldId);
    if (it != g_stacks.end() && oldId != newId) {
        const unsigned count = it->second.count;
        g_stacks.erase(it);
        g_stacks[newId] = {count, 0};  // type taken when first seen
    }
}

uint32_t StackWithRoom(const uint8_t* inventory, uint32_t type) {
    uint32_t found = 0;
    if (inventory && Stacks(inventory) && Stackable(type)) {
        game::ForEachGridItem(inventory, [&](uint32_t id) {
            if (!found && TypeOf(id) == type && StackCount(id) < kMaxStack) {
                found = id;
            }
        });
    }
    return found;
}

void ResetStacks() {
    std::lock_guard guard(g_lock);
    g_stacks.clear();
    g_entered.clear();
}

} // namespace mods::itemstack

namespace game {

using namespace mods::itemstack;

// cInventoryEntry::PlaceItem (0x5d9ec0, ret 0x14): (cell, id, w, h, notify).
int __fastcall Inv_PlaceItem(void* self, void* edx, uint32_t cell, uint32_t id, uint32_t w, uint32_t h, uint32_t notify);
RE_HOOK(0x005d9ec0, Inv_PlaceItem);
int __fastcall Inv_PlaceItem(void* self, void* edx, uint32_t cell, uint32_t id, uint32_t w, uint32_t h, uint32_t notify) {
    const int previous = Inv_PlaceItem_original(self, edx, cell, id, w, h, notify);
    if (!g_sorting && StackableItem(id) && Stacks(self)) {
        std::lock_guard guard(g_lock);
        g_entered.push_back({static_cast<uint8_t*>(self), id});
    }
    return previous;
}

// cInventoryEntry::RemoveItem (0x5da5f0, ret 8): (id, notify).
int __fastcall Inv_RemoveItem(void* self, void* edx, uint32_t id, uint32_t notify);
RE_HOOK(0x005da5f0, Inv_RemoveItem);
int __fastcall Inv_RemoveItem(void* self, void* edx, uint32_t id, uint32_t notify) {
    if (DrinkInProgress(id)) {
        return 1;
    }
    auto* item = static_cast<uint8_t*>(id ? GetObjectById(id) : nullptr);
    auto* flags = item ? reinterpret_cast<uint32_t*>(item + kObjectFlags) : nullptr;
    const unsigned count = flags && (*flags & kObjectUsedUp) ? StackCount(id) : 1;
    if (count > 1) {
        // A use from a stack: one less, the object stays.
        *flags &= ~kObjectUsedUp;
        SetStackCount(id, count - 1);
        g_drunk = id;
        g_drunkAt = GetTickCount();
        return 1;
    }
    return Inv_RemoveItem_original(self, edx, id, notify);
}

// cObjectManager::DestroyObject (0x5fbe10, ret 0x10): (id, 1, 0, 0) from UseItem.
uint32_t __fastcall ObjMgr_DestroyObject(void* self, void* edx, uint32_t id, uint32_t a, uint32_t b, uint32_t c);
RE_HOOK(0x005fbe10, ObjMgr_DestroyObject);
uint32_t __fastcall ObjMgr_DestroyObject(void* self, void* edx, uint32_t id, uint32_t a, uint32_t b, uint32_t c) {
    if (DrinkInProgress(id)) {
        return 0;
    }
    Forget(id);
    return ObjMgr_DestroyObject_original(self, edx, id, a, b, c);
}


// cCreature::UseItem (0x54a8f0, ret 4): a new drink starts (a
// Teleportationstrank opens the portal window instead, teleportpotion.cpp).
char __fastcall Creature_UseItem(void* self, void* edx, uint32_t id);
RE_HOOK(0x0054a8f0, Creature_UseItem);
char __fastcall Creature_UseItem(void* self, void* edx, uint32_t id) {
    g_drunk = 0;
    if (mods::teleportpotion::UseItem(self, id)) {
        return 0;
    }
    return Creature_UseItem_original(self, edx, id);
}

// cInventoryEntry::Sort (0x5db670, ret 4): stack first.
void __fastcall Inv_Sort(void* self, void* edx, uint32_t mode);
RE_HOOK(0x005db670, Inv_Sort);
void __fastcall Inv_Sort(void* self, void* edx, uint32_t mode) {
    if (Stacks(self)) {
        StackAll(static_cast<uint8_t*>(self));
    }
    g_sorting = true;
    Inv_Sort_original(self, edx, mode);
    g_sorting = false;
}

// cInventoryEntry::DrawItems (0x5dc3f0, ret 8): (renderer, flag); then the counts.
void __fastcall Inv_DrawItems(void* self, void* edx, void* renderer, uint32_t flag);
RE_HOOK(0x005dc3f0, Inv_DrawItems);
void __fastcall Inv_DrawItems(void* self, void* edx, void* renderer, uint32_t flag) {
    Inv_DrawItems_original(self, edx, renderer, flag);
    if (self) {
        DrawCounts(self, renderer);
    }
}

} // namespace game