feat: add depth sorting

sonic-radiance.love/birb/modules/gui/elements/parent.lua

@@ -20,7 +20,7 @@ end
 
 function GuiElement:register()
     local gui = self:getGui()
-    gui:addElement(self.name, self)
+    self.creationId = gui:addElement(self.name, self)
 end
 
 function GuiElement:destroy()

sonic-radiance.love/birb/modules/gui/mixins/elements.lua

@@ -3,10 +3,13 @@ local ElementList = Object:extend()
 function ElementList:initElements()
     self.elements = {}
     self.focusedElem = nil
+    self.nbrElement = 0
 end
 
 function ElementList:addElement(name, element)
+    self.nbrElement = self.nbrElement + 1
     self.elements[name] = element
+    return self.nbrElement
 end
 
 function ElementList:deleteElement(name)
@@ -22,6 +25,15 @@ function ElementList:getVisibleElement(topLayer)
             end
         end
     end
+
+    table.sort(visibleList, function (a, b)
+        if (a.depth == b.depth) then
+            return (a.creationId < b.creationId)
+        else
+            return (a.depth > b.depth)
+        end
+    end)
+
     return visibleList
 end