[MIRROR] Fix Transparent Floors Multi Z clipping [MDB IGNORE] (#10523)

* Fix Transparent Floors Multi Z clipping (#63878)

Fixes #63770 (Objects on Lower Z level appearing on top Z level when under glass tiles)

This fixes some MultiZ issues that were discovered after I made #62875 (566b9ee1d8). I never setup a new plane for the transparent turfs and because of this any objects, icons, or sprites that were offset from the boundary of the turf would make any bottom Z level stuff appear on the current Z level.

We want stuff to look normal.

* Fix Transparent Floors Multi Z clipping

Co-authored-by: Tim <timothymtorres@gmail.com>

code/__DEFINES/layers.dm

@@ -16,6 +16,8 @@
 #define GRAVITY_PULSE_RENDER_TARGET "*GRAVPULSE_RENDER_TARGET"
 
 #define OPENSPACE_LAYER 600 //Openspace layer over all
+
+#define TRANSPARENT_FLOOR_PLANE -10 //Transparent plane that shows openspace underneath the floor
 #define OPENSPACE_PLANE -9 //Openspace plane below all turfs
 #define OPENSPACE_BACKDROP_PLANE -8 //Black square just over openspace plane to guaranteed cover all in openspace turf
 

code/_onclick/hud/rendering/plane_master.dm

@@ -50,6 +50,13 @@
 	add_filter("second_stage_openspace", 2, drop_shadow_filter(color = "#04080FAA", size = -15))
 	add_filter("third_stage_openspace", 3, drop_shadow_filter(color = "#04080FAA", size = -20))
 
+///For any transparent multi-z tiles we want to render
+/atom/movable/screen/plane_master/transparent
+	name = "transparent plane master"
+	plane = TRANSPARENT_FLOOR_PLANE
+	appearance_flags = PLANE_MASTER
+	render_relay_plane = RENDER_PLANE_GAME
+
 ///Contains just the floor
 /atom/movable/screen/plane_master/floor
 	name = "floor plane master"

code/datums/elements/turf_transparency.dm

@@ -14,6 +14,8 @@
 	our_turf.layer = OPENSPACE_LAYER
 	if(is_openspace)
 		our_turf.plane = OPENSPACE_PLANE
+	else
+		our_turf.plane = TRANSPARENT_FLOOR_PLANE
 
 	RegisterSignal(target, COMSIG_TURF_MULTIZ_DEL, .proc/on_multiz_turf_del)
 	RegisterSignal(target, COMSIG_TURF_MULTIZ_NEW, .proc/on_multiz_turf_new)