WheelRotateUtil

WheelRotateAnimation = class("WheelRotateAnimation")
-- s = v0 * t + (a * t^2) / 2
-- a = (vt - v0) / t
local minSpeed
function WheelRotateAnimation:ctor( startAngle )
    self.maxSpeed = 360
    self.curSpeed =  0
    self.curAngle =startAngle
    self.accelerationSpeed= 0
    self.isSpeedingUp =false
    self.isSlowingDown =false
    self.targetAngle =0
    self.curDownTime = 0
end

function WheelRotateAnimation:SetMaxSpeedCallBack(callback)
    self.maxSpeedCallBack =callback
end

function WheelRotateAnimation:SetStopCallBack(callback )
    self.stopCallBack = callback
end

function WheelRotateAnimation:Start(startSpeed,accelerationSpeed)
    self.isSpeedingUp = true
    self.curSpeed =  startSpeed
    self.accelerationSpeed= accelerationSpeed
    self.isSlowingDown =false
end

function WheelRotateAnimation:Stop(targetAngle,slowDownTotalTime )
    local offsetAngle =0
    local curRealAngle = self:GetCurAngle()
    if targetAngle> curRealAngle then
        offsetAngle = targetAngle -curRealAngle
    else
        offsetAngle = 360 -(curRealAngle-targetAngle)
    end
    local totalDistance = 720 + offsetAngle
    --根据上面公式，我们想要在指定的时间内停下来，需要的加速度为
    self.accelerationSpeed = (2*totalDistance )/(slowDownTotalTime*slowDownTotalTime)
    self.isSlowingDown =true
    self.isSpeedingUp =false
    self.targetAngle = self.curAngle + totalDistance
    self.curDownTime =0
    self.maxSlowTime = slowDownTotalTime
end

function WheelRotateAnimation:Update( deltaTime )
    if self.isSpeedingUp then
        self.curSpeed = self.curSpeed + self.accelerationSpeed*deltaTime
        self.curSpeed = math.min(self.curSpeed,self.maxSpeed)
        if self.curSpeed>= self.maxSpeed then
            if self.maxSpeedCallBack then
                self.maxSpeedCallBack()
                self.maxSpeedCallBack =nil
            end
        end
        if self.curSpeed>0 then
            self.curAngle = self.curAngle + self.curSpeed * deltaTime
        end
    end

    self:CheckSlowDown(deltaTime)
end

function WheelRotateAnimation:CheckSlowDown(deltaTime)
    if self.isSlowingDown and self.curDownTime< self.maxSlowTime then
        self.curDownTime = self.curDownTime +deltaTime
        -- S =1/2 * a * t^2
        local progressTime = self.maxSlowTime - self.curDownTime
        self.slowDownDist = 0.5*self.accelerationSpeed*(progressTime*progressTime)
        self.curAngle = self.targetAngle - self.slowDownDist
        if self.curDownTime >= self.maxSlowTime then
            self.isSlowingDown=false
            self.curAngle = self.targetAngle
            if self.stopCallBack then
                self.stopCallBack()
                self.stopCallBack = nil
            end
        end
    end
end

--显示用的角度，只要0-360内
function WheelRotateAnimation:GetCurAngle()
    return math.floor(self.curAngle % 360)
end