Added PRESERVE_MOMENTUM PROJECTILE_SPECIAL flag

source_files/ddf/thing.cc

@@ -1675,6 +1675,7 @@ static const specflags_t normal_specials[] =
 	{"DROPPED", MF_DROPPED, 0},
 	{"CORPSE", MF_CORPSE, 0},
 	{"STEALTH", MF_STEALTH, 0},
+	{"PRESERVE_MOMENTUM", MF_PRESERVEMOMENTUM, 0},
 	{"DEATHMATCH", MF_NOTDMATCH, 1},
 	{"TOUCHY", MF_TOUCHY, 0},
 	{NULL, 0, 0}

source_files/ddf/thing.h

@@ -137,7 +137,8 @@ typedef enum
 	// Monster grows (in)visible at certain times.
 	MF_STEALTH = (1 << 26),
 
-	// NO LONGER USED (1 << 27), // was: JUSTPICKEDUP
+	// For projectiles: keep momentum of projectile source
+	MF_PRESERVEMOMENTUM = (1 << 27),
 
 	// Object reacts to being touched (often violently :->)
 	MF_TOUCHY = (1 << 28),

source_files/edge/p_action.cc

@@ -1227,6 +1227,12 @@ static mobj_t *DoLaunchProjectile(mobj_t * source, float tx, float ty, float tz,
 	}
 
 	P_SetMobjDirAndSpeed(projectile, angle, slope, projectile->speed);
+	if (projectile->flags & MF_PRESERVEMOMENTUM)
+	{
+		projectile->mom.x += source->mom.x;
+		projectile->mom.y += source->mom.y;
+		projectile->mom.z += source->mom.z;
+	}
 	CheckMissileSpawn(projectile);
 
 	return projectile;