diff --git a/lib/simple_ui/core/builder.lua b/lib/simple_ui/core/builder.lua
index d3878e4..5ec8c6e 100644
--- a/lib/simple_ui/core/builder.lua
+++ b/lib/simple_ui/core/builder.lua
@@ -1,37 +1,51 @@
+local Element = require "lib.simple_ui.core.element"
+
 --- Объект, который отвечает за работу с элементами интерфейса одного экрана
 --- @class UIBuilder
 --- @field private _cache UIElement[]
 --- @field elementTree UIElement
+--- @field private shadowTree UIElement
 local builder = {}
 builder.__index = builder
 
 --- @return UIBuilder
 local function new(from)
     from._cache = {}
-
+    from.shadowTree = Element:new {}
     setmetatable(from, builder)
     return from
 end
 
---- @param element? UIElement
+-- --- @param element? UIElement
+-- --- @private
+-- function builder:_get(element)
+--     if not element then return nil end
+--     local key = builder:_makeKey(element)
+--     if not key then return element end
+
+--     local cached = self._cache[key]
+--     if cached then return cached end
+
+--     self._cache[key] = element
+--     return element
+-- end
+
+--- @param newNode UIElement?
+--- @param oldNode UIElement?
 --- @private
-function builder:_get(element)
-    if not element then return nil end
-
-    local key = builder:_makeKey(element)
-    if not key then return element end
-
-    local cached = self._cache[key]
-    if cached then return cached end
-
-    self._cache[key] = element
-    return element
+function builder:didChange(newNode, oldNode)
+    if not oldNode or not newNode then
+        return true
+    end
+    if oldNode.type ~= newNode.type then return true end
+    if oldNode.key ~= newNode.key then return true end
+    return false
 end
 
 --- @param element UIElement
 --- @private
 function builder:_makeKey(element)
-    if not element.key then return nil end
+    --if not element.key then return nil end
     if type(element.key) == "string" then return element.key end
     element.key = element.type .. "<" .. tostring(element.key) .. ">"
     return element.key
@@ -39,18 +53,22 @@ end
 
 --- @private
 function builder:build_step(cur)
-    if not cur then return end
     if cur.build then
-        cur.child = self:_get(cur:build())
-        cur.child.parent = cur
+        local orphan = cur:build()
+        local child = cur.child
+        child = orphan
+        if not child then return end
+
+        child.parent = cur
+        cur.child = child
+
         self:build_step(cur.child)
     elseif cur.children then
         for _, child in ipairs(cur.children) do
-            self:build_step(self:_get(child))
+            child.parent = cur
+
+            self:build_step(child)
         end
-    else
-        cur.child = self:_get(cur.child)
-        self:build_step(cur.child)
     end
 end
 
@@ -58,7 +76,7 @@ end
 ---
 --- Благодаря этому можно каждый раз создавать новые элементы в верстке, а получать старые :)
 function builder:build()
-    local root = self:_get(self.elementTree)
+    local root = self.elementTree
     self:build_step(root)
 end
 
diff --git a/lib/simple_ui/core/element.lua b/lib/simple_ui/core/element.lua
index 721704d..d0cb78f 100644
--- a/lib/simple_ui/core/element.lua
+++ b/lib/simple_ui/core/element.lua
@@ -8,7 +8,7 @@ local Vec3 = require "lib.utils.vec3"
 --- @field constraints Constraints
 --- @field offset Vec3 Положение левого верхнего угла элемента в экранных координатах {x, y}. Устанавливается родительским элементом.
 --- @field size Vec3 Размеры элемента в экранных координатах {x, y}
---- @field build? fun(self): UIElement?
+--- @field build? fun(self, ctx: UIElement): UIElement
 local element = {}
 element.__index = element
 element.type = "Element"
@@ -23,7 +23,11 @@ function element:layout() end
 
 function element:update(dt) end
 
-function element:draw() end
+function element:draw()
+    if self.type == "SizedBox" then
+        print(self.offset)
+    end
+end
 
 --- @param values {[string]: any}
 --- @return UIElement
diff --git a/lib/simple_ui/core/multi_child_element.lua b/lib/simple_ui/core/multi_child_element.lua
index f3b1810..2bf383c 100644
--- a/lib/simple_ui/core/multi_child_element.lua
+++ b/lib/simple_ui/core/multi_child_element.lua
@@ -13,28 +13,30 @@ function element:update(dt)
 end
 
 function element:draw()
+    love.graphics.push("transform")
+    love.graphics.translate(self.offset.x, self.offset.y)
     for _, child in ipairs(self.children) do
         child:draw()
     end
 
+
     --- @TODO: сделать дебажный метод для отрисовки границ
     love.graphics.setColor(1, 0, 0)
-    love.graphics.line(self.offset.x, self.offset.y, self.offset.x + self.size.x, self.offset.y)
-    love.graphics.line(self.offset.x, self.offset.y, self.offset.x, self.offset.y + self.size.y)
-    love.graphics.line(self.offset.x + self.size.x, self.offset.y, self.offset.x + self.size.x,
-        self.offset.y + self.size.y)
-    love.graphics.line(self.offset.x, self.offset.y + self.size.y, self.offset.x + self.size.x,
-        self.offset.y + self.size.y)
+    love.graphics.line(0, 0, 0 + self.size.x, 0)
+    love.graphics.line(0, 0, 0, self.offset.y + 0)
+    love.graphics.line(0 + self.size.x, self.offset.y, 0 + self.size.x,
+        0 + self.size.y)
+    love.graphics.line(0, 0 + self.size.y, 0 + self.size.x,
+        0 + self.size.y)
     love.graphics.setColor(1, 1, 1)
+
+    love.graphics.pop()
 end
 
 --- @generic T : MultiChildElement
 --- @param values {children: UIElement[]?, [string]: any}
 --- @return T
 function element:new(values)
-    for _, child in ipairs(values.children or {}) do
-        child.parent = values
-    end
     return Element.new(self, values)
 end
 
diff --git a/lib/simple_ui/core/single_child_element.lua b/lib/simple_ui/core/single_child_element.lua
index 1f2086c..88c3094 100644
--- a/lib/simple_ui/core/single_child_element.lua
+++ b/lib/simple_ui/core/single_child_element.lua
@@ -1,15 +1,24 @@
 local Element = require "lib.simple_ui.core.element"
+local Constraints = require "lib.simple_ui.core.constraints"
 
 --- @class SingleChildElement : UIElement
 --- @field child? UIElement
 local element = setmetatable({}, require "lib.simple_ui.core.element")
 element.__index = element
 
+--- дефолтное поведение -- просто возвращать своего ребенка
+function element:build()
+    return self.child
+end
+
 function element:layout()
+    --- передать ребенку ограничения
+    --- получить назад размеры
+    --- разместить ребенка
     if not self.child then return end
-    self.child.constraints = self.constraints
+    self.child.constraints = Constraints(self.constraints)
     self.child:layout()
-    self.child.offset = self.offset:copy()
+    self.child.offset = Vec3 {}
 end
 
 function element:update(dt)
@@ -17,7 +26,10 @@ function element:update(dt)
 end
 
 function element:draw()
+    love.graphics.push("transform")
+    love.graphics.translate(self.offset.x, self.offset.y)
     if self.child then self.child:draw() end
+    love.graphics.pop()
 end
 
 --- @generic T : SingleChildElement
@@ -25,7 +37,6 @@ end
 --- @param values {child: UIElement?, [string]: any}
 --- @return T
 function element:new(values)
-    if values.child then values.child.parent = values end
     return Element.new(self, values)
 end
 
diff --git a/lib/simple_ui/elements/placeholder.lua b/lib/simple_ui/elements/placeholder.lua
index 93e53d5..10d0a9a 100644
--- a/lib/simple_ui/elements/placeholder.lua
+++ b/lib/simple_ui/elements/placeholder.lua
@@ -12,7 +12,6 @@ function element:layout()
     if not self.child then return end
     self.child.constraints = Constraints(self.constraints)
     self.child:layout()
-    self.child.offset = self.offset:copy()
 end
 
 function element:draw()
diff --git a/lib/simple_ui/elements/screen_area.lua b/lib/simple_ui/elements/screen_area.lua
index 6f5885c..7cb8253 100644
--- a/lib/simple_ui/elements/screen_area.lua
+++ b/lib/simple_ui/elements/screen_area.lua
@@ -15,10 +15,7 @@ function element:layout()
     self.size = Vec3 { screenW, screenH }
 
     if not self.child then return end
-    self.child.constraints = Constraints {
-        maxWidth = screenW,
-        maxHeight = screenH,
-    }
+    self.child.constraints = Constraints(self.constraints)
     self.child:layout()
     self.child.offset = Vec3 {}
 end
diff --git a/lib/simple_ui/elements/sized_box.lua b/lib/simple_ui/elements/sized_box.lua
index 7d5f5d1..0b5194e 100644
--- a/lib/simple_ui/elements/sized_box.lua
+++ b/lib/simple_ui/elements/sized_box.lua
@@ -17,7 +17,7 @@ function element:layout()
         maxHeight = self.height,
     }
     self.child:layout()
-    self.child.offset = self.offset:copy()
+    self.child.offset = Vec3 {}
 end
 
 --- @return SizedBox
diff --git a/lib/simple_ui/level/test.lua b/lib/simple_ui/level/test.lua
index d78e8d0..c567e92 100644
--- a/lib/simple_ui/level/test.lua
+++ b/lib/simple_ui/level/test.lua
@@ -3,25 +3,30 @@ local Placeholder = require "lib.simple_ui.elements.placeholder"
 local Padding = require "lib.simple_ui.elements.padding"
 local Builder = require "lib.simple_ui.core.builder"
 local Flex = require "lib.simple_ui.elements.flex"
+local Center = require "lib.simple_ui.elements.center"
 local SizedBox = require "lib.simple_ui.elements.sized_box"
 local SingleChildElement = require "lib.simple_ui.core.single_child_element"
 
 
 local MyWidget = setmetatable({}, SingleChildElement)
 MyWidget.__index = MyWidget
+MyWidget.type = "MyWidget"
 
 local Canary = setmetatable({}, SingleChildElement)
 Canary.__index = Canary
+Canary.type = "Canary"
 
 local reported = false
 function Canary:build()
-    if not reported then
-        self:traverseUp(function(element)
-            print(element.type)
-            return true
-        end)
-        reported = true
-    end
+    -- self.i = self.i and self.i + 1 or 0
+    -- print(self.i)
+    -- if not reported then
+    --     self:traverseUp(function(element)
+    --         print(element.type)
+    --         return true
+    --     end)
+    --     reported = true
+    -- end
 
     return Placeholder:new {}
 end
@@ -37,7 +42,6 @@ function MyWidget:build()
             Padding:new {
                 top = 8,
                 child = Flex:new {
-                    key = "inner_flex",
                     mainAxisAlignment = "start",
                     mainAxisSize = "min",
                     children = {
@@ -52,9 +56,12 @@ function MyWidget:build()
                             child = Placeholder:new {}
                         },
                         SizedBox:new {
+                            key = "mybox",
                             width = 100,
                             height = 100,
-                            child = Canary:new {}
+                            child = Canary:new {
+                                i = 10
+                            }
                         },
                     },
                 }
@@ -81,6 +88,35 @@ function MyWidget:build()
     }
 end
 
+--
+-- --- comment
+-- --- @return Flex
+-- function MyWidget:build()
+--     return Flex:new {
+--         mainAxisAlignment = "start",
+--         mainAxisSize = "min",
+--         children = {
+--             SizedBox:new {
+--                 width = 100,
+--                 height = 100,
+--                 child = Placeholder:new {}
+--             },
+--             SizedBox:new {
+--                 width = 150,
+--                 height = 200,
+--                 child = Placeholder:new {}
+--             },
+--             SizedBox:new {
+--                 width = 100,
+--                 height = 100,
+--                 child = Canary:new {
+--                     i = 10
+--                 }
+--             },
+--         },
+--     }
+-- end
+
 return Builder {
     elementTree = ScreenArea:new {
         child = MyWidget:new {}