cc_static_array.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

//=============================================================================
//
// CCStaticArray manages access to an array of script objects,
// where an element's size counted by script's bytecode may differ from the
// real element size in the engine's memory.
// The purpose of this is to remove size restriction from the engine's structs
// exposed to scripts.
//
// FIXME: [ivan-mogilko] the above was meant to work, but in reality it doesn't
// and won't, at least not without some extra workarounds.
// The problem that I missed here is following:
//   when the script compiler is told to get an Nth element of a global struct
//   array, such as character[n], it calculates the memory address as
//   array address + sizeof(Character) * n.
//   If this address is used for the read/write operations, these ops can be
//   intercepted by interpreter and remapped into the real fields
//      (see IScriptObject::ReadN, WriteN interface)
//   But if this address is used IN POINTER COMPARISON, then we cannot do
//   anything. And if our real struct in the engine is stored on a different
//   relative memory offset than one expected by compiler, then this pointer
//   comparison will fail, e.g. script expression like
//      if (player == character[n])
//
// NOTE: on the other hand, similar effect could be achieved by separating
// object data into two or more structs, where "base" structs are stored in
// the exposed arrays (part of API), while extending structs are stored
// separately. This is more an issue of engine data design.
//
//=============================================================================

#ifndef AGS_ENGINE_AC_DYNOBJ_STATIC_ARRAY_H
#define AGS_ENGINE_AC_DYNOBJ_STATIC_ARRAY_H

#include "ags/engine/ac/dynobj/cc_ags_dynamic_object.h"

namespace AGS3 {


struct CCStaticArray : public AGSCCStaticObject {
public:
    ~CCStaticArray() override {}

    void Create(IScriptObject *mgr, size_t elem_script_size, size_t elem_mem_size, size_t elem_count = SIZE_MAX /*unknown*/);

    inline IScriptObject *GetObjectManager() const {
        return _mgr;
    }

    // Legacy support for reading and writing object values by their relative offset
    inline void *GetElementPtr(void *address, intptr_t legacy_offset) {
        return static_cast<uint8_t *>(address) + (legacy_offset / _elemScriptSize) * _elemMemSize;
    }

    void    *GetFieldPtr(void *address, intptr_t offset) override;
    void    Read(void *address, intptr_t offset, uint8_t *dest, size_t size) override;
    uint8_t ReadInt8(void *address, intptr_t offset) override;
    int16_t ReadInt16(void *address, intptr_t offset) override;
    int32_t ReadInt32(void *address, intptr_t offset) override;
    float   ReadFloat(void *address, intptr_t offset) override;
    void    Write(void *address, intptr_t offset, const uint8_t *src, size_t size) override;
    void    WriteInt8(void *address, intptr_t offset, uint8_t val) override;
    void    WriteInt16(void *address, intptr_t offset, int16_t val) override;
    void    WriteInt32(void *address, intptr_t offset, int32_t val) override;
    void    WriteFloat(void *address, intptr_t offset, float val) override;

private:
    IScriptObject    *_mgr = nullptr;
    size_t           _elemScriptSize = 0u;
    size_t           _elemMemSize = 0u;
    size_t           _elemCount = 0u;
};

} // namespace AGS3

#endif