https://github.com/tgstation/tgstation/pull/79207

code/__DEFINES/dcs/signals/signals_mob/signals_mob_main.dm

@@ -68,8 +68,15 @@
 ///from base of mob/create_mob_hud(): ()
 #define COMSIG_MOB_HUD_CREATED "mob_hud_created"
 
-///from base of /mob/living/proc/apply_damage(): (damage, damagetype, def_zone)
+/// from /mob/living/proc/apply_damage(): (list/damage_mods, damage, damagetype, def_zone, sharpness, attack_direction, attacking_item)
+/// allows you to add multiplicative damage modifiers to the damage mods argument to adjust incoming damage
+/// not sent if the apply damage call was forced
+#define COMSIG_MOB_APPLY_DAMAGE_MODIFIERS "mob_apply_damage_modifiers"
+/// from base of /mob/living/proc/apply_damage(): (damage, damagetype, def_zone, blocked, sharpness, attack_direction, attacking_item)
 #define COMSIG_MOB_APPLY_DAMAGE "mob_apply_damage"
+/// from /mob/living/proc/apply_damage(): (damage, damagetype, def_zone, blocked, sharpness, attack_direction, attacking_item)
+/// works like above but after the damage is actually inflicted
+#define COMSIG_MOB_AFTER_APPLY_DAMAGE "mob_after_apply_damage"
 ///from base of /mob/living/attack_alien(): (user)
 #define COMSIG_MOB_ATTACK_ALIEN "mob_attack_alien"
 ///from base of /mob/throw_item(): (atom/target)

code/datums/components/explodable.dm

@@ -89,10 +89,17 @@
 
 	if(!def_zone)
 		return
+
 	if(damagetype != BURN) //Don't bother if it's not fire.
 		return
+
+	if(isbodypart(def_zone))
+		var/obj/item/bodypart/hitting = def_zone
+		def_zone = hitting.body_zone
+
 	if(!is_hitting_zone(def_zone)) //You didn't hit us! ha!
 		return
+
 	detonate()
 
 /datum/component/explodable/proc/on_equip(datum/source, mob/equipper, slot)

code/modules/antagonists/revolution/revolution.dm

@@ -273,7 +273,7 @@
 		owner.current.visible_message(span_deconversion_message("The frame beeps contentedly, suppressing the disloyal personality traits from the MMI before initalizing it."), null, null, null, owner.current)
 		to_chat(owner, span_userdanger("The frame's firmware detects and suppresses your unwanted personality traits! You feel more content with the leadership around these parts."))
 
-//blunt trauma deconversions call this through species.dm spec_attacked_by()
+//blunt trauma deconversions
 /datum/antagonist/rev/proc/remove_revolutionary(borged, deconverter)
 	owner.current.log_message("has been deconverted from the revolution by [ismob(deconverter) ? key_name(deconverter) : deconverter]!", LOG_ATTACK, color="#960000")
 	if(borged)

code/modules/mob/living/carbon/damage_procs.dm

@@ -1,43 +1,74 @@
 
 
-/mob/living/carbon/apply_damage(damage, damagetype = BRUTE, def_zone = null, blocked = FALSE, forced = FALSE, spread_damage = FALSE, sharpness = NONE, attack_direction = null, cap_loss_at = 0)
-	SEND_SIGNAL(src, COMSIG_MOB_APPLY_DAMAGE, damage, damagetype, def_zone)
-	var/hit_percent = (100-blocked)/100
-	if(!damage || (!forced && hit_percent <= 0))
-		return 0
+/mob/living/carbon/apply_damage(
+	damage = 0,
+	damagetype = BRUTE,
+	def_zone = null,
+	blocked = 0,
+	forced = FALSE,
+	spread_damage = FALSE,
+	sharpness = NONE,
+	attack_direction = null,
+	obj/item/attacking_item = null,
+)
+	// Spread damage should always have def zone be null
+	if(spread_damage)
+		def_zone = null
+
+	// Otherwise if def zone is null, we'll get a random bodypart / zone to hit.
+	// ALso we'll automatically covnert string def zones into bodyparts to pass into parent call.
+	else if(!isbodypart(def_zone))
+		var/random_zone = def_zone ? deprecise_zone(def_zone) : get_random_valid_zone(def_zone)
+		def_zone = get_bodypart(random_zone) || bodyparts[1]
+
+	. = ..()
+	// Taking brute or burn to bodyparts gives a damage flash
+	if(def_zone && (damagetype == BRUTE || damagetype == BURN))
+		damageoverlaytemp += .
+
+	return .
+
+/mob/living/carbon/human/apply_damage(
+	damage = 0,
+	damagetype = BRUTE,
+	def_zone = null,
+	blocked = 0,
+	forced = FALSE,
+	spread_damage = FALSE,
+	sharpness = NONE,
+	attack_direction = null,
+	obj/item/attacking_item = null,
+)
+
+	// Add relevant DR modifiers into blocked value to pass to parent
+	blocked += physiology?.damage_resistance
+	return ..()
 
-	var/obj/item/bodypart/BP = null
-	if(!spread_damage)
-		if(isbodypart(def_zone)) //we specified a bodypart object
-			BP = def_zone
-		else
-			if(!def_zone)
-				def_zone = ran_zone(def_zone)
-			BP = get_bodypart(deprecise_zone(def_zone))
-			if(!BP)
-				BP = bodyparts[1]
+/mob/living/carbon/human/get_incoming_damage_modifier(
+	damage = 0,
+	damagetype = BRUTE,
+	def_zone = null,
+	sharpness = NONE,
+	attack_direction = null,
+	attacking_item,
+)
+	. = ..()
 
-	var/damage_amount = forced ? damage : damage * hit_percent
 	switch(damagetype)
 		if(BRUTE)
-			if(BP)
-				BP.receive_damage(damage_amount, 0, sharpness = sharpness)
-			else //no bodypart, we deal damage with a more general method.
-				adjustBruteLoss(damage_amount, forced = forced)
+			. *= physiology.brute_mod
 		if(BURN)
-			if(BP)
-				BP.receive_damage(0, damage_amount, sharpness = sharpness)
-			else
-				adjustFireLoss(damage_amount, forced = forced)
+			. *= physiology.burn_mod
 		if(TOX)
-			adjustToxLoss(damage_amount, forced = forced)
-		if(OXY)
-			adjustOxyLoss(damage_amount, forced = forced)
+			. *= physiology.tox_mod
 		if(CLONE)
-			adjustCloneLoss(damage_amount, forced = forced)
+			. *= physiology.clone_mod
 		if(STAMINA)
-			CRASH("apply_damage tried to adjust stamina loss!")
-	return TRUE
+			. *= physiology.stamina_mod
+		if(BRAIN)
+			. *= physiology.brain_mod
+
+	return .
 
 
 //These procs fetch a cumulative total damage from all bodyparts

code/modules/mob/living/carbon/human/human_defense.dm

@@ -131,42 +131,6 @@
 
 	return FALSE
 
-/mob/living/carbon/human/attacked_by(obj/item/I, mob/living/user)
-	var/target_zone = deprecise_zone(user.zone_selected) //our intended target
-
-	var/obj/item/bodypart/affecting = get_bodypart(target_zone)
-	if (!affecting || affecting.is_stump)
-		to_chat(user, span_danger("They do not have a [parse_zone(target_zone)]"))
-		return MOB_ATTACKEDBY_FAIL
-
-	// If we aren't being hit by ourself, roll for accuracy.
-	if(user != src)
-		var/bodyzone_modifier = GLOB.bodyzone_gurps_mods[target_zone]
-		var/roll
-		if(HAS_TRAIT(user, TRAIT_PERFECT_ATTACKER))
-			roll = SUCCESS
-		else
-			roll = user.stat_roll(10, /datum/rpg_skill/skirmish, bodyzone_modifier, -7, src).outcome
-
-		var/hit_zone
-		switch(roll)
-			if(CRIT_FAILURE)
-				visible_message(span_danger("\The [user] swings at [src] with \the [I], narrowly missing!"))
-				return MOB_ATTACKEDBY_MISS
-
-			if(FAILURE)
-				hit_zone = get_random_valid_zone()
-			else
-				hit_zone = target_zone
-
-		affecting = get_bodypart(hit_zone)
-
-	SEND_SIGNAL(I, COMSIG_ITEM_ATTACK_ZONE, src, user, affecting)
-
-	// the attacked_by code varies among species
-	return dna.species.spec_attacked_by(I, user, affecting, src)
-
-
 /mob/living/carbon/human/attack_hulk(mob/living/carbon/human/user)
 	. = ..()
 	if(!.)

code/modules/mob/living/carbon/human/physiology.dm

@@ -1,19 +1,34 @@
 //Stores several modifiers in a way that isn't cleared by changing species
 
 /datum/physiology
-	var/brute_mod = 1 // % of brute damage taken from all sources
-	var/burn_mod = 1 // % of burn damage taken from all sources
-	var/tox_mod = 1 // % of toxin damage taken from all sources
-	var/oxy_mod = 1 // % of oxygen damage taken from all sources
-	var/clone_mod = 1 // % of clone damage taken from all sources
-	var/stamina_mod = 1 // % of stamina damage taken from all sources
-	var/brain_mod = 1 // % of brain damage taken from all sources
-
-	var/pressure_mod = 1 // % of brute damage taken from low or high pressure (stacks with brute_mod)
-	var/heat_mod = 1 // % of burn damage taken from heat (stacks with burn_mod)
-	var/cold_mod = 1 // % of burn damage taken from cold (stacks with burn_mod)
-
-	var/damage_resistance = 0 // %damage reduction from all sources
+	/// Multiplier to brute damage received.
+	/// IE: A brute mod of 0.9 = 10% less brute damage.
+	/// Only applies to damage dealt via [apply_damage][/mob/living/proc/apply_damage] unless factored in manually.
+	var/brute_mod = 1
+	/// Multiplier to burn damage received
+	var/burn_mod = 1
+	/// Multiplier to toxin damage received
+	var/tox_mod = 1
+	/// Multiplier to oxygen damage received
+	var/oxy_mod = 1
+	/// Multiplier to clone damage received
+	var/clone_mod = 1
+	/// Multiplier to stamina damage received
+	var/stamina_mod = 1
+	/// Multiplier to brain damage received
+	var/brain_mod = 1
+
+	/// Multiplier to damage taken from high / low pressure exposure, stacking with the brute modifier
+	var/pressure_mod = 1
+	/// Multiplier to damage taken from high temperature exposure, stacking with the burn modifier
+	var/heat_mod = 1
+	/// Multiplier to damage taken from low temperature exposure, stacking with the toxin modifier
+	var/cold_mod = 1
+
+	/// Flat damage reduction from taking damage
+	/// Unlike the other modifiers, this is not a multiplier.
+	/// IE: DR of 10 = 10% less damage.
+	var/damage_resistance = 0
 
 	var/siemens_coeff = 1 // resistance to shocks