Adds (fake) ambient occlusion as a client preference

code/__DEFINES/layers.dm

@@ -6,6 +6,7 @@
 #define PLANE_SPACE -95
 #define PLANE_SPACE_PARALLAX -90
 
+#define FLOOR_PLANE -2
 #define GAME_PLANE -1
 #define BLACKNESS_PLANE 0 //To keep from conflicts with SEE_BLACKNESS internals
 #define SPACE_LAYER 1.8

code/__DEFINES/misc.dm

@@ -445,3 +445,6 @@ GLOBAL_LIST_INIT(ghost_others_options, list(GHOST_OTHERS_SIMPLE, GHOST_OTHERS_DE
 #define NO_INIT_PARAMETER "no-init"
 
 #define EGG_LAYING_MESSAGES list("lays an egg.","squats down and croons.","begins making a huge racket.","begins clucking raucously.")
+
+//Filters
+#define AMBIENT_OCCLUSION filter(type="drop_shadow", x=0, y=-2, size=4, border=4, color="#04080FAA")