Add getLeader helper for monsters in a pack

Source/loadsave.cpp

@@ -659,6 +659,8 @@ void LoadMonster(LoadHelper *file, Monster &monster)
 	if (monster.talkMsg == TEXT_KING1) // Fix original bad mapping of NONE for monsters
 		monster.talkMsg = TEXT_NONE;
 	monster.leader = file->NextLE<uint8_t>();
+	if (monster.leader == 0)
+		monster.leader = Monster::NoLeader; // Golems shouldn't be leaders of other monsters
 	monster.leaderRelation = static_cast<LeaderRelation>(file->NextLE<uint8_t>());
 	monster.packSize = file->NextLE<uint8_t>();
 	monster.lightId = file->NextLE<int8_t>();
@@ -1400,8 +1402,8 @@ void SaveMonster(SaveHelper *file, Monster &monster)
 	file->WriteLE<uint16_t>(monster.magicResistance);
 	file->Skip(2); // Alignment
 
-	file->WriteLE<int32_t>(monster.talkMsg == TEXT_NONE ? 0 : monster.talkMsg); // Replicate original bad mapping of none for monsters
-	file->WriteLE<uint8_t>(monster.leader);
+	file->WriteLE<int32_t>(monster.talkMsg == TEXT_NONE ? 0 : monster.talkMsg);       // Replicate original bad mapping of none for monsters
+	file->WriteLE<uint8_t>(monster.leader == Monster::NoLeader ? 0 : monster.leader); // Vanilla uses 0 as the default leader which corresponds to player 0s golem
 	file->WriteLE<uint8_t>(static_cast<std::uint8_t>(monster.leaderRelation));
 	file->WriteLE<uint8_t>(monster.packSize);
 	// vanilla compatibility

Source/monster.cpp

@@ -241,7 +241,7 @@ void InitMonster(Monster &monster, Direction rd, int mtype, Point position)
 	monster.maxDamage2 = monster.data().mMaxDamage2;
 	monster.armorClass = monster.data().mArmorClass;
 	monster.magicResistance = monster.data().mMagicRes;
-	monster.leader = 0;
+	monster.leader = Monster::NoLeader;
 	monster.leaderRelation = LeaderRelation::None;
 	monster.flags = monster.data().mFlags;
 	monster.talkMsg = TEXT_NONE;
@@ -1754,18 +1754,18 @@ bool IsLineNotSolid(Point startPoint, Point endPoint)
 
 void FollowTheLeader(Monster &monster)
 {
-	if (monster.leader == 0)
+	if (monster.leaderRelation != LeaderRelation::Leashed)
 		return;
 
-	if (monster.leaderRelation != LeaderRelation::Leashed)
+	Monster *leader = monster.getLeader();
+	if (leader == nullptr)
 		return;
 
-	auto &leader = Monsters[monster.leader];
-	if (monster.activeForTicks >= leader.activeForTicks)
+	if (monster.activeForTicks >= leader->activeForTicks)
 		return;
 
-	monster.position.last = leader.position.tile;
-	monster.activeForTicks = leader.activeForTicks - 1;
+	monster.position.last = leader->position.tile;
+	monster.activeForTicks = leader->activeForTicks - 1;
 }
 
 void GroupUnity(Monster &monster)
@@ -1773,12 +1773,12 @@ void GroupUnity(Monster &monster)
 	if (monster.leaderRelation == LeaderRelation::None)
 		return;
 
-	// Someone with a leaderRelation should have a leader ...
-	assert(monster.leader >= 0);
-	// And no unique monster would be a minion of someone else!
+	// No unique monster would be a minion of someone else!
 	assert(monster.uniqType == 0);
 
-	auto &leader = Monsters[monster.leader];
+	// Someone with a leaderRelation should have a leader, if we end up trying to access a nullptr then the relation was already broken...
+
+	auto &leader = *monster.getLeader();
 	if (IsLineNotSolid(monster.position.tile, leader.position.future)) {
 		if (monster.leaderRelation == LeaderRelation::Separated
 		    && monster.position.tile.WalkingDistance(leader.position.future) < 4) {
@@ -2345,7 +2345,7 @@ void ScavengerAi(int monsterId)
 	if (monster.hitPoints < (monster.maxHitPoints / 2) && monster.goal != MonsterGoal::Healing) {
 		if (monster.leaderRelation != LeaderRelation::None) {
 			if (monster.leaderRelation == LeaderRelation::Leashed)
-				Monsters[monster.leader].packSize--;
+				monster.getLeader()->packSize--;
 			monster.leaderRelation = LeaderRelation::None;
 		}
 		monster.goal = MonsterGoal::Healing;
@@ -4007,12 +4007,12 @@ void M_UpdateLeader(int monsterId)
 
 	for (size_t j = 0; j < ActiveMonsterCount; j++) {
 		auto &minion = Monsters[ActiveMonsters[j]];
-		if (minion.leaderRelation == LeaderRelation::Leashed && minion.leader == monsterId)
+		if (minion.leaderRelation == LeaderRelation::Leashed && minion.getLeader() == &monster)
 			minion.leaderRelation = LeaderRelation::None;
 	}
 
 	if (monster.leaderRelation == LeaderRelation::Leashed) {
-		Monsters[monster.leader].packSize--;
+		monster.getLeader()->packSize--;
 	}
 }
 
@@ -4296,7 +4296,7 @@ bool DirOK(int monsterId, Direction mdir)
 	if (!IsRelativeMoveOK(monster, position, mdir))
 		return false;
 	if (monster.leaderRelation == LeaderRelation::Leashed) {
-		return futurePosition.WalkingDistance(Monsters[monster.leader].position.future) < 4;
+		return futurePosition.WalkingDistance(monster.getLeader()->position.future) < 4;
 	}
 	if (monster.uniqType == 0 || UniqueMonstersData[monster.uniqType - 1].monsterPack != UniqueMonsterPack::Leashed)
 		return true;
@@ -4310,7 +4310,7 @@ bool DirOK(int monsterId, Direction mdir)
 				continue;
 
 			auto &minion = Monsters[mi - 1];
-			if (minion.leaderRelation == LeaderRelation::Leashed && minion.leader == monsterId) {
+			if (minion.leaderRelation == LeaderRelation::Leashed && minion.getLeader() == &monster) {
 				mcount++;
 			}
 		}
@@ -4845,6 +4845,14 @@ void decode_enemy(Monster &monster, int enemyId)
 	return std::distance<const Monster *>(&Monsters[0], this);
 }
 
+Monster *Monster::getLeader() const
+{
+	if (leader == Monster::NoLeader)
+		return nullptr;
+
+	return &Monsters[leader];
+}
+
 void Monster::checkStandAnimationIsLoaded(Direction mdir)
 {
 	if (IsAnyOf(mode, MonsterMode::Stand, MonsterMode::Talk)) {

Source/monster.h

@@ -239,6 +239,8 @@ struct Monster { // note: missing field _mAFNum
 	uint8_t packSize;
 	int8_t lightId;
 
+	static constexpr uint8_t NoLeader = -1;
+
 	/**
 	 * @brief Sets the current cell sprite to match the desired desiredDirection and animation sequence
 	 * @param graphic Animation sequence of interest
@@ -289,6 +291,8 @@ struct Monster { // note: missing field _mAFNum
 	 */
 	[[nodiscard]] size_t getId() const;
 
+	[[nodiscard]] Monster *getLeader() const;
+
 	/**
 	 * @brief Is the monster currently walking?
 	 */

Source/qol/monhealthbar.cpp

@@ -136,7 +136,7 @@ void DrawMonsterHealthBar(const Surface &out)
 	DrawString(out, monster.name, { position + Displacement { -1, 1 }, { width, height } }, style | UiFlags::ColorBlack);
 	if (monster.uniqType != 0)
 		style |= UiFlags::ColorWhitegold;
-	else if (monster.leader != 0)
+	else if (monster.leader != Monster::NoLeader)
 		style |= UiFlags::ColorBlue;
 	else
 		style |= UiFlags::ColorWhite;