- Finally has the right idea how to restore Doom's original clipping of projectiles

against decorations without breaking anything newer:
  Added a new 'projectilepassheight' property that defines an alternative height
  that is only used when checking a projectile's movement against this actor.
  If the value is positive it is used regardless of other settings, if it is
  negative, its absolute will be used if a new compatibility option is enabled
  and if it is 0 the normal height will be used.


SVN r1253 (trunk)

src/p_map.cpp

@@ -745,8 +745,24 @@ bool PIT_CheckThing (AActor *thing, FCheckPosition &tm)
 		{
 			return true;
 		}
+
+		int clipheight;
+		
+		if (thing->projectilepassheight > 0) 
+		{
+			clipheight = thing->projectilepassheight;
+		}
+		else if (thing->projectilepassheight < 0 && (i_compatflags & COMPATF_MISSILECLIP))
+		{
+			clipheight = -thing->projectilepassheight;
+		}
+		else
+		{
+			clipheight = thing->height;
+		}
+
 		// Check if it went over / under
-		if (tm.thing->z > thing->z + thing->height)
+		if (tm.thing->z > thing->z + clipheight)
 		{ // Over thing
 			return true;
 		}