Improves bullet projectile embedding handling

Commit b1546ee3eb contained a rather
bone-headed mistake, that resulted in embedding with penetrating
projectiles to not behave as desired.

This commit fixes that, and provides a cleaner implementation.

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

@@ -38,9 +38,9 @@ emp_act
 				return -1 // complete projectile permutation
 
 	//Shrapnel
-	if (P.can_embed())
+	if(P.can_embed())
 		var/armor = getarmor_organ(organ, "bullet")
-		if(P.embed && prob(20 + max(P.damage - armor, -10)))
+		if(prob(20 + max(P.damage - armor, -10)))
 			var/obj/item/weapon/shard/shrapnel/SP = new()
 			SP.name = (P.name != "shrapnel")? "[P.name] shrapnel" : "shrapnel"
 			SP.desc = "[SP.desc] It looks like it was fired from [P.shot_from]."

code/modules/projectiles/projectile.dm

@@ -66,14 +66,10 @@
 	return
 
 //Checks if the projectile is eligible for embedding. Not that it necessarily will.
-//Mainly used to ensure that projectiles won't embed if they are penetrating the mob.
 /obj/item/projectile/proc/can_embed()
 	//embed must be enabled and damage type must be brute
 	if(!embed || damage_type != BRUTE)
 		return 0
-	//can't embed if the projectile is penetrating through the mob
-	if(penetrating > 0 && damage > 20 && prob(damage))
-		return 0
 	return 1
 
 //return 1 if the projectile should be allowed to pass through after all, 0 if not.
@@ -206,9 +202,9 @@
 			for(var/mob/M in A)
 				attack_mob(M, distance)
 
-	//penetrating projectiles can pass through things that otherwise would not let them
+	//penetrating projectiles can pass through things that otherwise would not let them
 	if(!passthrough && penetrating > 0)
-		if(check_penetrate(A))
+		if(check_penetrate(A))
 			passthrough = 1
 		penetrating--
 
@@ -311,4 +307,4 @@
 	trace.firer = user
 	var/output = trace.process() //Test it!
 	del(trace) //No need for it anymore
-	return output //Send it back to the gun!
+	return output //Send it back to the gun!

code/modules/projectiles/projectile/bullets.dm

@@ -7,23 +7,37 @@
 	check_armour = "bullet"
 	embed = 1
 	sharp = 1
+	var/mob_passthrough_check = 0
 
 /obj/item/projectile/bullet/on_hit(var/atom/target, var/blocked = 0)
 	if (..(target, blocked))
 		var/mob/living/L = target
 		shake_camera(L, 3, 2)
 
+/obj/item/projectile/bullet/attack_mob(var/mob/living/target_mob, var/distance, var/miss_modifier)
+	if(penetrating > 0 && damage > 20 && prob(damage))
+		mob_passthrough_check = 1
+	else
+		mob_passthrough_check = 0
+	..()
+
+/obj/item/projectile/bullet/can_embed()
+	//prevent embedding if the projectile is passing through the mob
+	if(mob_passthrough_check)
+		return 0
+	return ..()
+
 /obj/item/projectile/bullet/check_penetrate(var/atom/A)
-	if(!A || !A.density) return 1 //if whatever it was got destroyed when we hit it, then I guess we can just keep going
+	if(!A || !A.density) return 1 //if whatever it was got destroyed when we hit it, then I guess we can just keep going
 
 	if(istype(A, /obj/mecha))
 		return 1 //mecha have their own penetration handling
 
 	if(ismob(A))
+		if (!mob_passthrough_check)
+			return 0
 		if(iscarbon(A))
-			//squishy mobs absorb KE
-			if(can_embed()) return 0
-			damage *= 0.7
+			damage *= 0.7 //squishy mobs absorb KE
 		return 1
 
 	var/chance = 0