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BattleSystem.md

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Overview of the call stack on vanilla battle-system:

ActionCombat
├── InitObstacleBattleUnit
├── BattleGenerateReal
│   └── BattleGenerateRealInternal
│       ├── InitBattleUnit: Unit2BattleHook
│       ├── SetBattleUnitWeapon
│       ├── BattleInitTargetCanCounter: CheckCanCounter
│       ├── BattleApplyWeaponTriangleEffect: WeaponTriangle
│       ├── BattleGenerate
│       │   ├── ComputeBattleUnitStats: PreBattleCalc
│       │   │   ├── ...
│       │   │   ├── ComputeBattleUnitAttack
│       │   │   │   ├── IsUnitEffectiveAgainst
│       │   │   │   └── IsItemEffectiveAgainst
│       │   │   └── ...
│       │   ├── ComputeBattleUnitEffectiveStats: BattlcCalcReal
│       │   │   ├── ComputeBattleUnitEffectiveHitRate
│       │   │   ├── ComputeBattleUnitEffectiveCritRate
│       │   │   ├── ComputeBattleUnitSilencerRate
│       │   │   └── ComputeBattleUnitSpecialWeaponStats
│       │   └── BattleUnwind
│       │       ├── BattleGetFollowUpOrder
│       │       └── BattleGenerateRoundHits
│       │           ├── GetBattleUnitHitCount
│       │           └── BattleGenerateHit
│       │               ├── BattleUpdateBattleStats
│       │               ├── BattleGenerateHitTriangleAttack: removed and put into PreBattleCalc
│       │               ├── BattleGenerateHitAttributes
│       │               │   ├── BattleCheckSureShot
│       │               │   ├── BattleCheckGreatShield
│       │               │   ├── BattleCheckPierce
│       │               │   ├── BattleCheckSilencer
│       │               │   └── BattleCheckPetrify
│       │               └── BattleGenerateHitEffects
│       ├── BattleUnitTargetCheckCanCounter
│       ├── BattleUnitTargetSetEquippedWeapon: mainly setup for banim UI, if unit has no weapon, give a weapon to show.
│       └── BattleApplyExpGains
│           ├── GetBattleUnitExpGain
│           └── CheckBattleUnitLevelUp
└── sProcScr_CombatAction
    ├── BeginBattleAnimations
    ├── BattleApplyGameStateUpdates
    │   └── BattleApplyUnitUpdates
    │       └── UpdateUnitFromBattle
    └── BATTLE_HandleCombatDeaths

Damage calc formula

result = ([atk + correction - def]) * (100% + increase%) * (100%  + crit_correction%) / (100% + decrease%) + real_damage

Hp drain

In vanilla, it directly uses BattleHit::hpChange to determine hp drain amount for each round.

In C-SkillSys, in order to modify hp drain, the amound is stored in gExtBattleHitArray, which is recorded round by round. If there hold hp-drain in one round, then flag BATTLE_HIT_ATTR_HPSTEAL should also be set in BattleHit::attributes, which is just consistent to vanilla.

In C-SkillSys, Hp drain is mainly calculated by function BattleHit_CalcHpDrain, which will be called after damage calculation. Meanwhile, an external API AppendHpDrain can also register the hp drain amount.

The related round anim effect functions are also directly rewriten:

  • banim: ParseBattleHitToBanimCmd
  • mapanim: MapAnim_BeginRoundSpecificAnims

Hp cost

The HP cost is a new combat mechanic introduced in the c-Skillsys, inspired by the Gaiden magic system. The related code is mainly stored in BattleSys/HpCost and BattleSys/RoundAnim directory.

It is important to note the HP cost is designed COMPLETE DIFFERENT from regular battle damage. It is initiated proactively by the attacker before each battle round. The HP cost is non-lethal and can only be triggered when the user's HP is above a predefined threshold. The kernel stores this value in ExtBattleHit::hp_cost to preserve the value for each round. In principle, developers are not encouraged to directly modify this value in ext-hit. Instead, the kernel provides dedicated APIs for developers to register the HP cost:

bool TryBattleHpCost(struct BattleUnit *bu, int hp_cost);
bool AddBattleHpCost(struct BattleUnit *bu, int round, int cost);

The anim effect on hp cost is also seperated designed:

  • MapAnim

The hp-cost process is registered to pre-round hook gPreMapAnimBattleRoundHooks, which will insert the anim of the attacer's HP reduction after skill icon displaying and before round based attack anim starting.

  • Banim

The hp-cost will allocate separate slot in EfxHpLut for each round if an HP cost exists via ParseBattleHitToBanimCmd. Then display the hp-cost anim and advance the hp-lut offset gEfxHpLutOff when anim command C07 is executed.

Weapon slot expansion

Taking gaiden/TH/engage style weapon system into consideration, the battle weapon slot is expanded:

  • 0-4: unit items
  • 5: special item (dance ring)
  • 6-7: arena
  • 8: ballista
  • 9-15: (CHAX) gaiden B.Magic
  • 16-22: (CHAX) gaiden W.Magic
  • 23-36: (CHAX, preserved) ThreeHouses style magic
  • 37-42: (CHAX, preserved) Engage style weapon

It should be noted that as for now the weapon slot index may cause overflow on Unit::items, it is DANGROUS to directly find the item by unit->items[slot], as an alternative, kernel has offered the specific API to get weapon from slot:

#include <battle-system.h>

int GetItemFromSlot(struct Unit *unit, int slot);

Battle weapon auto-equipment