Add checks to ignore renewal DEF (#7150)

* Fixes #7143.
* Resolves an issue where Dragon Breath, Dragon Breath - Water, Cart Cannon, and Arms Cannon were not properly reducing damage based on the target's defense.
Thanks to @LadyNanuia, @Lemongrass3110, @attackjom!

src/map/battle.cpp

@@ -5750,22 +5750,40 @@ static void battle_calc_defense_reduction(struct Damage* wd, struct block_list *
 	}
 
 #ifdef RENEWAL
-	/**
-	 * RE DEF Reduction
-	 * Damage = Attack * (4000+eDEF)/(4000+eDEF*10) - sDEF
-	 * Pierce defence gains 1 atk per def/2
-	 */
-	if( def1 == -400 ) /* -400 creates a division by 0 and subsequently crashes */
-		def1 = -399;
-	ATK_ADD2(wd->damage, wd->damage2,
-		is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_R) ? (def1*battle_calc_attack_skill_ratio(wd, src, target, skill_id, skill_lv))/200 : 0,
-		is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_L) ? (def1*battle_calc_attack_skill_ratio(wd, src, target, skill_id, skill_lv))/200 : 0
-	);
-	if( !attack_ignores_def(wd, src, target, skill_id, skill_lv, EQI_HAND_R) && !is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_R) )
-		wd->damage = wd->damage * (4000+def1) / (4000+10*def1) - vit_def;
-	if( is_attack_left_handed(src, skill_id) && !attack_ignores_def(wd, src, target, skill_id, skill_lv, EQI_HAND_L) && !is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_L) )
-		wd->damage2 = wd->damage2 * (4000+def1) / (4000+10*def1) - vit_def;
-
+	switch(skill_id) {
+		case RK_DRAGONBREATH:
+		case RK_DRAGONBREATH_WATER:
+		case NC_ARMSCANNON:
+		case GN_CARTCANNON:
+			if (attack_ignores_def(wd, src, target, skill_id, skill_lv, EQI_HAND_R) || attack_ignores_def(wd, src, target, skill_id, skill_lv, EQI_HAND_L))
+				return;
+			if (is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_R) || is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_L))
+				return;
+
+			// Defense reduction by flat value.
+			// This completely bypasses the normal RE DEF Reduction formula.
+			wd->damage -= (def1 + vit_def);
+			if (is_attack_left_handed(src, skill_id))
+				wd->damage2 -= (def1 + vit_def);
+			break;
+		/**
+		 * RE DEF Reduction
+		 * Damage = Attack * (4000+eDEF)/(4000+eDEF*10) - sDEF
+		 * Pierce defence gains 1 atk per def/2
+		 */
+		default:
+			if( def1 == -400 ) /* -400 creates a division by 0 and subsequently crashes */
+				def1 = -399;
+			ATK_ADD2(wd->damage, wd->damage2,
+				is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_R) ? (def1*battle_calc_attack_skill_ratio(wd, src, target, skill_id, skill_lv))/200 : 0,
+				is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_L) ? (def1*battle_calc_attack_skill_ratio(wd, src, target, skill_id, skill_lv))/200 : 0
+			);
+			if( !attack_ignores_def(wd, src, target, skill_id, skill_lv, EQI_HAND_R) && !is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_R) )
+				wd->damage = wd->damage * (4000+def1) / (4000+10*def1) - vit_def;
+			if( is_attack_left_handed(src, skill_id) && !attack_ignores_def(wd, src, target, skill_id, skill_lv, EQI_HAND_L) && !is_attack_piercing(wd, src, target, skill_id, skill_lv, EQI_HAND_L) )
+				wd->damage2 = wd->damage2 * (4000+def1) / (4000+10*def1) - vit_def;
+			break;
+	}
 #else
 		if (def1 > 100) def1 = 100;
 		ATK_RATE2(wd->damage, wd->damage2,