Avoid overflow of tickCounterOfCurrentFrame (#4893)

* When MFLAG_ALLOW_SPECIAL is set, don't call processAnimation (avoid overflow of tickCounterOfCurrentFrame)

Source/engine/animationinfo.cpp

@@ -185,11 +185,9 @@ void AnimationInfo::changeAnimationData(OptionalCelSprite celSprite, int8_t numb
 	this->celSprite = celSprite;
 }
 
-void AnimationInfo::processAnimation(bool reverseAnimation /*= false*/, bool dontProgressAnimation /*= false*/)
+void AnimationInfo::processAnimation(bool reverseAnimation /*= false*/)
 {
 	tickCounterOfCurrentFrame++;
-	if (dontProgressAnimation)
-		return;
 	ticksSinceSequenceStarted_++;
 	if (tickCounterOfCurrentFrame >= ticksPerFrame) {
 		tickCounterOfCurrentFrame = 0;

Source/engine/animationinfo.h

@@ -97,7 +97,7 @@ public:
 	 * @param reverseAnimation Play the animation backwards (for example is used for "unseen" monster fading)
 	 * @param dontProgressAnimation Increase tickCounterOfCurrentFrame but don't change currentFrame
 	 */
-	void processAnimation(bool reverseAnimation = false, bool dontProgressAnimation = false);
+	void processAnimation(bool reverseAnimation = false);
 
 private:
 	/**

Source/loadsave.cpp

@@ -593,7 +593,8 @@ void LoadMonster(LoadHelper *file, Monster &monster)
 	file->Skip(4); // Skip pointer _mAnimData
 	monster.AnimInfo = {};
 	monster.AnimInfo.ticksPerFrame = file->NextLENarrow<int32_t, int8_t>();
-	monster.AnimInfo.tickCounterOfCurrentFrame = file->NextLENarrow<int32_t, int8_t>();
+	// Ensure that we can increase the tickCounterOfCurrentFrame at least once without overflow (needed for backwards compatibility for sitting gargoyles)
+	monster.AnimInfo.tickCounterOfCurrentFrame = file->NextLENarrow<int32_t, int8_t>(1) - 1;
 	monster.AnimInfo.numberOfFrames = file->NextLENarrow<int32_t, int8_t>();
 	monster.AnimInfo.currentFrame = file->NextLENarrow<int32_t, int8_t>(-1);
 	file->Skip(4); // Skip _meflag

Source/monster.cpp

@@ -1464,7 +1464,7 @@ bool MonsterRangedSpecialAttack(int monsterId)
 	assert(monsterId >= 0 && monsterId < MaxMonsters);
 	auto &monster = Monsters[monsterId];
 
-	if (monster.AnimInfo.currentFrame == monster.data().mAFNum2 - 1 && monster.AnimInfo.tickCounterOfCurrentFrame == 0) {
+	if (monster.AnimInfo.currentFrame == monster.data().mAFNum2 - 1 && monster.AnimInfo.tickCounterOfCurrentFrame == 0 && (monster._mAi != AI_MEGA || monster._mVar2 == 0)) {
 		if (AddMissile(
 		        monster.position.tile,
 		        monster.enemyPosition,
@@ -4282,8 +4282,8 @@ void ProcessMonsters()
 				GroupUnity(monster);
 			}
 		} while (raflag);
-		if (monster._mmode != MonsterMode::Petrified) {
-			monster.AnimInfo.processAnimation((monster._mFlags & MFLAG_LOCK_ANIMATION) != 0, (monster._mFlags & MFLAG_ALLOW_SPECIAL) != 0);
+		if (monster._mmode != MonsterMode::Petrified && (monster._mFlags & MFLAG_ALLOW_SPECIAL) == 0) {
+			monster.AnimInfo.processAnimation((monster._mFlags & MFLAG_LOCK_ANIMATION) != 0);
 		}
 	}