diff --git a/cherry/engine/camera.lua b/cherry/engine/camera.lua
deleted file mode 100644
index 59ab810..0000000
--- a/cherry/engine/camera.lua
+++ /dev/null
@@ -1,127 +0,0 @@
---------------------------------------------------------------------------------
-
-local _ = require 'cherry.libs.underscore'
-
-local Camera = {
-  options = {},
-  display = display.newGroup(),
-  zoom = 1
-}
-
---------------------------------------------------------------------------------
-
-local INIT_X = display.contentWidth * 0.5
-local INIT_Y = display.contentHeight * 0.5
-
---------------------------------------------------------------------------------
-
-local xShake = 16
-local yShake = 8
-local shakePeriod = 2
-
---------------------------------------------------------------------------------
-
-function Camera:insert(stuff)
-  self.display:insert(stuff)
-end
-
-function Camera:localToContent(x, y)
-  self.display:localToContent(x, y)
-end
-
---------------------------------------------------------------------------------
-
-function Camera:empty()
-  display.remove(self.display)
-  self.display = display.newGroup()
-end
-
---------------------------------------------------------------------------------
-
-function Camera:resetZoom()
-  self.zoom = 1
-end
-
---------------------------------------------------------------------------------
-
-function Camera:toHUD(vector)
-  local alpha = math.rad(Camera.display.rotation)
-  local cameraX = vector.x * Camera.zoom
-  local cameraY = vector.y * Camera.zoom
-
-  local x = cameraX * math.cos(alpha) - cameraY * math.sin(alpha)
-  local y = cameraX * math.sin(alpha) + cameraY * math.cos(alpha)
-
-  return x + Camera.display.x, y + Camera.display.y
-end
-
---------------------------------------------------------------------------------
-
--- INIT_X,Y should be defined by the current level offset from level[0,0]
--- default for Doors : not offset = the center of the screen = level[0,0]
-function Camera:center()
-  self.display.x = INIT_X
-  self.display.y = INIT_Y
-
-  -- reset then apply
-  self.display.xScale = 1
-  self.display.yScale = 1
-  self.display:scale(self.zoom, self.zoom)
-end
-
---------------------------------------------------------------------------------
-
-function Camera:start(options)
-  self.options = _.extend(self.options, options)
-  transition.cancel(self.display)
-  self.display.alpha = 1
-  App.hud:toFront()
-
-  self.moveDisplay = function()
-    if (self.shakeCount % shakePeriod == 0) then
-      self.display.x = self.display.x0 + math.random(-xShake, xShake)
-      self.display.y = self.display.y0 + math.random(-yShake, yShake)
-    end
-    self.shakeCount = self.shakeCount + 1
-  end
-
-  self.startShake = function()
-    self.display.x0 = self.display.x
-    self.display.y0 = self.display.y
-    self.shakeCount = 0
-    Runtime:addEventListener('enterFrame', self.moveDisplay)
-  end
-
-  self.stopShake = function()
-    Runtime:removeEventListener('enterFrame', self.moveDisplay)
-    self.display.x = INIT_X
-    self.display.y = INIT_Y
-    self.shaking = false
-  end
-end
-
-function Camera:shake()
-  if (self.shaking) then
-    timer.cancel(self.shaking)
-    self.stopShake()
-  end
-
-  self.startShake()
-  self.shaking = timer.performWithDelay(250, self.stopShake)
-end
-
-function Camera:stop()
-  transition.to(
-    self.display,
-    {
-      alpha = 0,
-      time = 500,
-      xScale = 0.01,
-      yScale = 0.01
-    }
-  )
-end
-
---------------------------------------------------------------------------------
-
-return Camera
diff --git a/cherry/engine/effects.lua b/cherry/engine/effects.lua
deleted file mode 100644
index 3f40368..0000000
--- a/cherry/engine/effects.lua
+++ /dev/null
@@ -1,166 +0,0 @@
---------------------------------------------------------------------------------
-
-local Effects = {
-    effects = {},
-}
-
-local nbDestroyed = 0
-local nbRunning   = 0
-
---------------------------------------------------------------------------------
-
-function Effects:start()
-    self:startAllEffects()
-end
-
-function Effects:pause()
-    -- Runtime:removeEventListener( 'enterFrame', refreshEffects )
-end
-
-function Effects:stop(now)
-    self:pause()
-
-    if(self.effects) then
-        while #self.effects > 0 do
-            self:destroyEffect(self.effects[1])
-        end
-    end
-
-    self.effects = {}
-    nbDestroyed  = 0
-    nbRunning    = 0
-end
-
-function Effects:restart()
-    self:pause(true)
-    self:start()
-end
-
---------------------------------------------------------------------------------
--- for static views : no refresh required
-function Effects:startAllEffects()
-    if(self.effects) then
-        for i=1,#self.effects do
-            self:startEffect(self.effects[i])
-        end
-    end
-end
-
---------------------------------------------------------------------------------
-
-function Effects:registerNewEffect( effect )
-    effect.num = #self.effects+1
-    self.effects[effect.num] = effect
-end
-
---------------------------------------------------------------------------------
-
-function Effects:startEffect( effect )
-    if(not effect.started) then
-        effect:start()
-        effect.started = true
-
-        --- debug
-        nbRunning = nbRunning + 1
-    end
-end
-
---------------------------------------------------------------------------------
-
-function Effects:stopEffect( effect )
-    effect:stop()
-    effect.started = false
-
-    --- debug
-    nbRunning = nbRunning - 1
-end
-
---------------------------------------------------------------------------------
-
-function Effects:destroyEffect( effect, now )
-    table.removeObject(self.effects, effect)
-    effect:destroy()
-
-    nbDestroyed = nbDestroyed + 1
-end
-
---------------------------------------------------------------------------------
-
-function Effects:destroyObjectWithEffect(body)
-    if(body.effect) then
-        return self:destroyEffect(body.effect)
-    else
-        return false
-    end
-end
-
---------------------------------------------------------------------------------
---- Menu Atmospheres
---------------------------------------------------------------------------------
-
-function Effects:atmosphere(parent, x, y, scale)
-    local effect = CBE.newVent({
-        preset = 'wisps',
-        emitX = x,
-        emitY = y
-    })
-
-    self:registerNewEffect(effect)
-    parent:insert(effect)
-    return effect
-end
-
------------------------------------------------------------------------------
---- Explosion
------------------------------------------------------------------------------
-
-function Effects:explosion(parent, x, y)
-    local vent = CBE.newVent({
-        preset = 'wisps',
-        title = 'explosion',
-        scale = 1.7,
-        positionType = 'inRadius',
-        color = {{1, 1, 0}, {1, 0.5, 0}, {0.2, 0.2, 0.2}},
-        particleProperties = {blendMode = 'add'},
-        emitX = x,
-        emitY = y,
-
-        emissionNum = 3,
-        emitDelay = 15,
-        perEmit = 2,
-
-        inTime = 100,
-        lifeTime = 0,
-        outTime = 200,
-
-        onCreation = function(particle)
-            particle:changeColor({
-                color = {0.1, 0.1, 0.1},
-                time = 500
-            })
-        end,
-
-        onUpdate = function(particle)
-            particle:setCBEProperty('  scaleRateX'   , particle:getCBEProperty('scaleRateX' ) * 0.998)
-            particle:setCBEProperty('  scaleRateY'   , particle:getCBEProperty('scaleRateY' ) * 0.998)
-        end,
-
-        physics = {
-            velocity = 0,
-            gravityY = -0.035,
-            scaleRateX = 1,
-            scaleRateY = 1,
-            autoCalculateAngles = true,
-            angles = {{60, 120}, {120, 60}}, -- Add angles in form of 60-120-60
-            cycleAngle = true
-        }
-    })
-
-    self:registerNewEffect(vent)
-    parent:insert(vent)
-    self:restart()
-end
-
---------------------------------------------------------------------------------
-
-return Effects
diff --git a/cherry/engine/game.lua b/cherry/engine/game.lua
index bb797f2..37596d8 100644
--- a/cherry/engine/game.lua
+++ b/cherry/engine/game.lua
@@ -2,7 +2,6 @@
 
 local Background = require 'cherry.components.background'
 local Screen = require 'cherry.components.screen'
-local Effects = require 'cherry.engine.effects'
 local colorize = require 'cherry.libs.colorize'
 local _ = require 'cherry.libs.underscore'
 
@@ -18,6 +17,7 @@ function Game:new(extension)
     extension,
     {
       isRunning = false,
+      camera = nil,
       preset = {}, -- may be used to set a preset data during `resetState`
       state = {},
       elements = {}
@@ -29,18 +29,66 @@ function Game:new(extension)
 end
 
 --------------------------------------------------------------------------------
+-- these should be implemented by extension
 
 function Game:initialState()
   return {}
 end
+
 function Game:resetState()
   self.state = self:initialState()
 end
+
+function Game:resetElements()
+  self.elements = {}
+end
+
+--------------------------------------------------------------------------------
+
 function Game:getState()
   return self.state
 end
-function Game:resetElements()
-  self.elements = {}
+
+--------------------------------------------------------------------------------
+
+function Game:resetCamera()
+  if (self.camera) then
+    display.remove(self.camera)
+  end
+
+  self.camera = display.newGroup()
+  App.reorderLayers()
+end
+
+function Game:removeCamera()
+  transition.to(
+    self.camera,
+    {
+      alpha = 0,
+      time = 500,
+      xScale = 0.01,
+      yScale = 0.01,
+      x = W / 2,
+      y = H / 2,
+      onComplete = function()
+        display.remove(self.camera)
+      end
+    }
+  )
+end
+
+function Game:growCamera()
+  transition.from(
+    self.camera,
+    {
+      alpha = 0,
+      time = 500,
+      xScale = 0.01,
+      yScale = 0.01,
+      x = W / 2,
+      y = H / 2
+    }
+  )
 end
 
 --------------------------------------------------------------------------------
@@ -48,20 +96,20 @@ end
 --------------------------------------------------------------------------------
 
 function Game:reset()
-  display.remove(App.hud)
-  App.hud = display.newGroup()
-
   if (self.onReset) then
     self:onReset()
   end -- from extension
 
-  Camera:empty()
   self:resetState()
   self:resetElements()
+  self:resetCamera()
+
   App.score:reset()
   self.preset = {} -- by now preset should have been used to init state and can be reset
 end
 
+--------------------------------------------------------------------------------
+
 function Game:run()
   self.isRunning = true
 
@@ -71,19 +119,13 @@ function Game:run()
     _G.physics.setGravity(App.xGravity, App.yGravity)
   end
 
-  Camera:resetZoom()
-  Camera:center()
-  Camera:start()
-
+  self:growCamera()
   Background:darken()
 
   if (self.onRun) then
     self:onRun()
   end -- from extension
 
-  if (_G.CBE) then
-    Effects:restart()
-  end
   print('Game runs.')
 end
 
@@ -140,12 +182,8 @@ function Game:stop(noScore)
 
   ------------------------------------------
 
+  self:removeCamera()
   Background:lighten()
-  if (_G.CBE) then
-    Effects:stop(true)
-  end
-
-  Camera:stop()
 end
 
 --------------------------------------------------------------------------------
diff --git a/cherry/main.lua b/cherry/main.lua
index 41b5ca2..7efc905 100644
--- a/cherry/main.lua
+++ b/cherry/main.lua
@@ -1,5 +1,5 @@
 --------------------------------------------------------------------------------
-_G.CHERRY_VERSION = '3.1.0'
+_G.CHERRY_VERSION = '3.2.0'
 --------------------------------------------------------------------------------
 -- debug
 require 'cherry.libs.logger'
@@ -19,8 +19,6 @@ _G.App = require 'cherry.core.app'
 _G.Router = require 'cherry.core.router'
 
 -- engine
-_G.Camera = require 'cherry.engine.camera'
-_G.Effects = require 'cherry.engine.effects'
 _G.Game = require 'cherry.engine.game'
 _G.Sound = require 'cherry.engine.sound'
 
diff --git a/docs/camera-shaking.md b/docs/camera-shaking.md
new file mode 100644
index 0000000..92dadd9
--- /dev/null
+++ b/docs/camera-shaking.md
@@ -0,0 +1,43 @@
+backup camera shaking.
+
+```lua
+function Camera:start(options)
+  _G.log('🔴 Camera is DEPRECATED! use App.game.camera instead.')
+  self.options = _.extend(self.options, options)
+  transition.cancel(self.display)
+  self.display.alpha = 1
+  App.hud:toFront()
+
+  self.moveDisplay = function()
+    if (self.shakeCount % shakePeriod == 0) then
+      self.display.x = self.display.x0 + math.random(-xShake, xShake)
+      self.display.y = self.display.y0 + math.random(-yShake, yShake)
+    end
+    self.shakeCount = self.shakeCount + 1
+  end
+
+  self.startShake = function()
+    self.display.x0 = self.display.x
+    self.display.y0 = self.display.y
+    self.shakeCount = 0
+    Runtime:addEventListener('enterFrame', self.moveDisplay)
+  end
+
+  self.stopShake = function()
+    Runtime:removeEventListener('enterFrame', self.moveDisplay)
+    self.display.x = INIT_X
+    self.display.y = INIT_Y
+    self.shaking = false
+  end
+end
+
+function Camera:shake()
+  if (self.shaking) then
+    timer.cancel(self.shaking)
+    self.stopShake()
+  end
+
+  self.startShake()
+  self.shaking = timer.performWithDelay(250, self.stopShake)
+end
+```
diff --git a/readme.md b/readme.md
index d7bc7a0..aa8f830 100644
--- a/readme.md
+++ b/readme.md
@@ -98,6 +98,17 @@ A typical tree should be :
 
 ## Using Cherry
 
+### Layers
+
+from back to front:
+
+- `Background`: global to the app, not reset by Router
+- `App.transversalBackLayer`: global to the app, not reset by Router
+- `self.view`: local to current composer view
+- `App.transversalFrontLayer`: global to the app, not reset by Router
+- `App.hud`: local to each view, reset by Router
+  Game.elements use `App.hud` as parent, and allow cross callbacks.
+
 ### Adding a new Screen
 
 A `Screen` implements the [Composer](https://docs.coronalabs.com/daily/api/library/composer/index.html) library.