Port current /tg/ lighting system

code/modules/modular_computers/computers/modular_computer/core.dm

@@ -72,22 +72,34 @@
 /obj/item/modular_computer/update_icon()
 	icon_state = icon_state_unpowered
 
-	overlays.Cut()
+	cut_overlays()
+
+	. = list()
+
 	if(bsod)
-		overlays += image(icon = overlay_icon, icon_state = "bsod")
-		return
+		. += mutable_appearance(overlay_icon, "bsod")
+		. += emissive_appearance(overlay_icon, "bsod")
+		return add_overlay(.)
 	if(!enabled)
 		if(icon_state_screensaver)
-			overlays += image(icon = overlay_icon, icon_state = icon_state_screensaver)
+			. += mutable_appearance(overlay_icon, icon_state_screensaver)
+			. += emissive_appearance(overlay_icon, icon_state_screensaver)
 		set_light(0)
-		return
+		return add_overlay(.)
+	
 	set_light(light_strength)
+	
 	if(active_program)
-		overlays += image(icon = overlay_icon, icon_state = active_program.program_icon_state ? active_program.program_icon_state : icon_state_menu)
+		var/program_state = active_program.program_icon_state ? active_program.program_icon_state : icon_state_menu
+		. += mutable_appearance(overlay_icon, program_state)
+		. += emissive_appearance(overlay_icon, program_state)
 		if(active_program.program_key_state)
-			overlays += image(icon = overlay_icon, icon_state = active_program.program_key_state)
+			. += mutable_appearance(overlay_icon, active_program.program_key_state)
 	else
-		overlays += image(icon = overlay_icon, icon_state = icon_state_menu)
+		. += mutable_appearance(overlay_icon, icon_state_menu)
+		. += emissive_appearance(overlay_icon, icon_state_menu)
+	
+	return add_overlay(.)
 
 /obj/item/modular_computer/proc/turn_on(var/mob/user)
 	if(bsod)

code/modules/modular_computers/computers/modular_computer/variables.dm

@@ -24,6 +24,7 @@
 	// If you create a program which is limited to Laptops and Consoles you don't have to add it's icon_state overlay for Tablets too, for example.
 
 	icon = null												// This thing isn't meant to be used on it's own. Subtypes should supply their own icon.
+	blocks_emissive = FALSE
 	var/overlay_icon = null									// Icon file used for overlays
 	icon_state = null
 	center_of_mass = null									// No pixelshifting by placing on tables, etc.

code/modules/modular_computers/computers/subtypes/dev_laptop.dm

@@ -41,7 +41,7 @@
 	if(anchored)
 		..()
 	else
-		overlays.Cut()
+		cut_overlays()
 		set_light(0)		// No glow from closed laptops
 		icon_state = icon_state_closed