Merge pull request #12596 from Ghommie/Ghommie-cit819

Porting further material datum features and improvements.

code/game/atoms.dm

@@ -48,6 +48,7 @@
 	var/rad_insulation = RAD_NO_INSULATION
 
 	///The custom materials this atom is made of, used by a lot of things like furniture, walls, and floors (if I finish the functionality, that is.)
+	///The list referenced by this var can be shared by multiple objects and should not be directly modified. Instead, use [set_custom_materials][/atom/proc/set_custom_materials].
 	var/list/custom_materials
 	///Bitfield for how the atom handles materials.
 	var/material_flags = NONE
@@ -114,11 +115,8 @@
 	if (canSmoothWith)
 		canSmoothWith = typelist("canSmoothWith", canSmoothWith)
 
-	var/temp_list = list()
-	for(var/i in custom_materials)
-		temp_list[SSmaterials.GetMaterialRef(i)] = custom_materials[i] //Get the proper instanced version
-	custom_materials = null //Null the list to prepare for applying the materials properly
-	set_custom_materials(temp_list)
+	// apply materials properly from the default custom_materials value
+	set_custom_materials(custom_materials)
 
 	ComponentInitialize()
 
@@ -1012,26 +1010,21 @@ Proc for attack log creation, because really why not
 
 ///Sets the custom materials for an item.
 /atom/proc/set_custom_materials(var/list/materials, multiplier = 1)
-
-	if(!materials)
-		materials = custom_materials
-
 	if(custom_materials) //Only runs if custom materials existed at first. Should usually be the case but check anyways
 		for(var/i in custom_materials)
 			var/datum/material/custom_material = SSmaterials.GetMaterialRef(i)
 			custom_material.on_removed(src, material_flags) //Remove the current materials
 
 	if(!length(materials))
+		custom_materials = null
 		return
 
-	custom_materials = list() //Reset the list
+	if(material_flags & MATERIAL_EFFECTS)
+		for(var/x in materials)
+			var/datum/material/custom_material = SSmaterials.GetMaterialRef(x)
+			custom_material.on_applied(src, materials[x] * multiplier * material_modifier, material_flags)
 
-	for(var/x in materials)
-		var/datum/material/custom_material = SSmaterials.GetMaterialRef(x)
-
-		if(material_flags & MATERIAL_EFFECTS)
-			custom_material.on_applied(src, materials[custom_material] * multiplier * material_modifier, material_flags)
-		custom_materials[custom_material] += materials[x] * multiplier
+	custom_materials = SSmaterials.FindOrCreateMaterialCombo(materials, multiplier)
 
 /**
   * Returns true if this atom has gravity for the passed in turf