Another Shake

bowerandy · May 2013

Folks,

I wasn't too happy with some of the other "shake" examples that I'd seen so here is another attempt that based around some Flash ActrionScript that I found here:

http://stackoverflow.com/a/13714372/1691412

This is what it looks like:

And here's the code:

function Sprite:shake(duration, distance, angle, ease, frequency)
 
	local function outExponential(ratio)
		-- Just in case easing.lua is not available
		if ratio == 1 then return 1 end
		return 1-math.pow(2, -10 * ratio)
	end
 
	if self._shakeTimer then
		-- Kill any existing shake
		local e=Event.new(Event.TIMER_COMPLETE)
		self._shakeTimer:dispatchEvent(e)
	end
 
	duration=duration or 0.5
	distance=distance or 30
	frequency=frequency or 100
	angle = angle or 0
	ease=ease or outExponential
 
	local shakes=math.floor(duration*frequency)
	local shakeTimer=Timer.new(1000/frequency, shakes)
	local startX, startY=self:getPosition()
	local startRot=self:getRotation()
	local count=0
 
	local function shakeUpdate(e)
		count=count+1
		local amplitude=1-ease(count/shakes)
		local x=startX+(-distance / 2 + math.random()*distance)*amplitude
		local y=startY+(-distance / 2 + math.random()*distance)*amplitude
		local rot=startRot+(-angle / 2 + math.random()*angle)*amplitude
		self:setPosition(x, y)
		self:setRotation(rot)
	end
 
	local function shakeComplete(e)
		self:setPosition(startX, startY)
		self:setRotation(startRot)
		shakeTimer:removeEventListener(Event.TIMER, shakeUpdate)
		shakeTimer:removeEventListener(Event.TIMER_COMPLETE, shakeComplete)
		self._shakeTimer=nil
	end
 
	shakeTimer:addEventListener(Event.TIMER, shakeUpdate)
	shakeTimer:addEventListener(Event.TIMER_COMPLETE, shakeComplete)
	shakeTimer:start()
	self._shakeTimer=shakeTimer
end
 
-- Shake example
local boing=Sound.new("Boing.wav")
application:setBackgroundColor(0x76BAF1)
 
local button=Bitmap.new(Texture.new("HelpButton.png"))
stage:addChild(button)
button:setAnchorPoint(0.5, 0.5)
button:setPosition(240, 160)
 
button:addEventListener(Event.TOUCHES_BEGIN, 
	function() 
		boing:play()
		button:shake(0.8, 50, 10)
	end)

The default parameters give a reasonable shake but you can obviously tailor them as desired. It's probably best not to set a shake angle unless the object you are shaking has an anchor point set to its centre.

best regards

hgvyas123 · May 2013

k000000l

bravcm · June 2013

Thanks!!

Apollo14 · September 2019

Hey guys! Recently I was watching one interesting youtube video and became curious about shaking effects. And I've found this topic.

The Sprite:shake() function as described here works perfectly well and it's extremely useful! Let's add more juice to our games

P.s. Btw we can shake whole stage as well (since stage is also a Sprite)

stage:shake(4,50,10)

And one little question:
Sprites do shake around anchorpoint, which is usually '0,0' and sometimes it's inconvenient to centrify it to '0.5,0.5'.
Are there any workaround to shake Sprite around its center without changing its anchorpoint to '0.5,0.5'?

Cheers!

MoKaLux · September 2019

just what I was looking for, thank you @Apollo14

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