From cc801a7efac8fc5d38d9efd87af7c228c55c5794 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Tue, 29 Jun 2021 17:33:16 +0200
Subject: [PATCH] - MBF21: added projectile group.

---
 src/gamedata/d_dehacked.cpp           |  7 +++++++
 src/playsim/p_map.cpp                 | 26 +++++++++++++++++++++++++-
 src/scripting/thingdef_properties.cpp | 13 +++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/src/gamedata/d_dehacked.cpp b/src/gamedata/d_dehacked.cpp
index 3e9011b2a..ad62d1b61 100644
--- a/src/gamedata/d_dehacked.cpp
+++ b/src/gamedata/d_dehacked.cpp
@@ -971,6 +971,13 @@ static int PatchThing (int thingy)
 			}
 			type->ActorInfo()->infighting_group = grp;
 		}
+		else if (linelen == 16 && stricmp(Line1, "projectile group") == 0)
+		{
+			stripwhite(Line2);
+			int grp = atoi(Line2);
+			if (grp < 0) grp = -1;
+			type->ActorInfo()->projectile_group = grp;
+		}
 
 		else if (linelen > 6)
 		{
diff --git a/src/playsim/p_map.cpp b/src/playsim/p_map.cpp
index 64172fa20..0e6e42ffe 100644
--- a/src/playsim/p_map.cpp
+++ b/src/playsim/p_map.cpp
@@ -1157,6 +1157,29 @@ static bool CheckRipLevel(AActor *victim, AActor *projectile)
 //
 //==========================================================================
 
+static bool P_ProjectileImmune(AActor* target, AActor* source)
+{
+	// This one's directly taken from DSDA.
+	auto targetgroup = target->GetClass()->ActorInfo()->projectile_group;
+	auto sourcegroup = source->GetClass()->ActorInfo()->projectile_group;
+
+	return
+		( // PG_GROUPLESS means no immunity, even to own species
+			targetgroup != -1/*PG_GROUPLESS*/ ||
+			target == source
+			) &&
+		(
+			( // target type has default behaviour, and things are the same type
+				targetgroup == 0/*PG_DEFAULT*/ &&
+				(source->GetSpecies() == target->GetSpecies() && !(target->flags6 & MF6_DOHARMSPECIES))
+				) ||
+			( // target type has special behaviour, and things have the same group
+				targetgroup != 0/*PG_DEFAULT*/ &&
+				targetgroup == sourcegroup
+				)
+			);
+}
+
 static bool CanAttackHurt(AActor *victim, AActor *shooter)
 {
 	// players are never subject to infighting settings and are always allowed
@@ -1204,7 +1227,8 @@ static bool CanAttackHurt(AActor *victim, AActor *shooter)
 					// [RH] Don't hurt monsters that hate the same victim as you do
 					return false;
 				}
-				if (victim->GetSpecies() == shooter->GetSpecies() && !(victim->flags6 & MF6_DOHARMSPECIES))
+
+				if (P_ProjectileImmune(victim, shooter))
 				{
 					// Don't hurt same species or any relative -
 					// but only if the target isn't one's hostile.
diff --git a/src/scripting/thingdef_properties.cpp b/src/scripting/thingdef_properties.cpp
index 2120ae97b..0367b8caf 100644
--- a/src/scripting/thingdef_properties.cpp
+++ b/src/scripting/thingdef_properties.cpp
@@ -1038,6 +1038,19 @@ DEFINE_PROPERTY(infightinggroup, I, Actor)
 	info->ActorInfo()->infighting_group = i;
 }
 
+//==========================================================================
+// MBF21
+//==========================================================================
+DEFINE_PROPERTY(projectilegroup, I, Actor)
+{
+	PROP_INT_PARM(i, 0);
+	if (i < -1)
+	{
+		I_Error("Projectile groups must be >= -1.");
+	}
+	info->ActorInfo()->projectile_group = i;
+}
+
 //==========================================================================
 // [BB]
 //==========================================================================