local TestScene = class("TestScene", function()
 return display.newScene("TestScene")
end)

function TestScene:ctor()
 
end

function TestScene:onEnter()
 self:initUI()
end

function TestScene:initUI()
 --刮刮卡底层容器
 local scratchLayer = display.newLayer()
 scratchLayer:setContentSize(self:getBoundingBox())
 self:addChild(scratchLayer)

 scratchLayer:setTouchEnabled(true)
 scratchLayer:setTouchMode(cc.TOUCH_MODE_ONE_BY_ONE)

 --创建RenderTexture
 local scratch = cc.RenderTexture:create(scratchLayer:getBoundingBox().width,scratchLayer:getBoundingBox().height)
 scratch:setPosition(scratchLayer:getBoundingBox().width/2,scratchLayer:getBoundingBox().height/2)
 scratch:retain()

 --需要被挂掉的精灵 本文以纯白背景代替
 local bg = cc.Sprite:createWithTexture(nil, cc.rect(0,0 , scratchLayer:getBoundingBox().width,scratchLayer:getBoundingBox().height))
 bg:setColor(cc.c3b(255,255,255))
 bg:setPosition(scratchLayer:getBoundingBox().width/2,scratchLayer:getBoundingBox().height/2)

 --渲染
 scratch:begin()
 bg:visit()
 scratch:endToLua()

 scratchLayer:addChild(scratch)

 --利用DrawNode创建模拟的刮除媒介
 local eraser = cc.DrawNode:create()
 --刮除媒介是个圆 半径为20 具体可自行定义
 local r = 20

 eraser:drawSolidCircle(cc.p(0,0),
 r,
 0,
 r,
 1,
 1,
 cc.c4f(0,0,0,0)
 )

 eraser:retain()

 --开始添加触摸事件
 scratchLayer:addNodeEventListener(cc.NODE_TOUCH_EVENT, function (event)
 --首先把点击区域刮除
 eraser:setPosition(event.x,event.y)

 eraser:setBlendFunc(gl.ONE,gl.ZERO)

 scratch:begin()
 eraser:visit()

 --[[
  重点：因为点击事件回调次数限制，如果没有下面处理，
  当我们快速在屏幕上滑动的时候调用次数不够，会产生一个一个刮除点
  而中间并没有刮除。
  以下代码为刮除两次移动中间矩形区域
 ]]
 local isEnded = false
 if event.name ~= "began" then
  if eraser.lastPos then
  --矩形宽高
  local width = self:getP2PDis(event, eraser.lastPos)
  local height = 2*r
  --矩形中点
  local midPos = cc.p((event.x+eraser.lastPos.x)/2,(event.y+eraser.lastPos.y)/2)
  --旋转角度
  local rotate = self:getP2PAngle(eraser.lastPos, event)

  --矩形刮除媒介
  local polygonEraser = cc.DrawNode:create()
  local points = {
   cc.p(-width/2,-height/2),
   cc.p(-width/2,height/2),
   cc.p(width/2,height/2),
   cc.p(width/2,-height/2)
  }
  polygonEraser:drawPolygon(points, {
   fillColor = cc.c4f(0, 0, 0, 0),
   borderWidth = 1,
   borderColor = cc.c4f(0, 0, 0, 0),
  })

  --刮除矩形区域
  polygonEraser:setRotation(-rotate)

  polygonEraser:setPosition(midPos)

  polygonEraser:setBlendFunc(gl.ONE,gl.ZERO)

  polygonEraser:visit()
  scratch:endToLua()
  isEnded = true
  end
 end

 if not isEnded then
  scratch:endToLua()
 end

 eraser.lastPos = cc.p(event.x,event.y)

 if event.name == "ended" then
  eraser.lastPos = nil
 end

 return true
 end)
end

--两点间距
function TestScene:getP2PDis(p1,p2)
 local x = p1.x - p2.x
  local y = p1.y - p2.y
  return math.abs(math.sqrt(math.pow(x,2)+math.pow(y,2)))
end

--两点连接线倾斜角度
function TestScene:getP2PAngle(p1,p2)
  local x = p1.x - p2.x
  local y = p1.y - p2.y
  return 180 * (math.atan2(y, x) / math.pi)
end

return TestScene