GTween swapValues causes screen flicker

bowerandy · September 2012

Folks,

When I was putting together my popup class (see this post), I noticed that use of the swapValues option in a GTween seems to cause an unpleasant flicker at the start of the animation. Actually, I've noticed the effect before but it slipped my mind until now.

You can see the effect in my popup demo video (below) at times 1:10 and 3:04 and 3:11. When the popup is dismissed, I use swapValues to reverse the GTween used for the entry transition (the flicker actually occurs on all exit transitions but the video doesn't pick it up every case).

Any ideas?

Best regards

bowerandy · September 2012

Ok, after looking at it a bit more, I can now answer my own question.

The problem is caused in GTween:swapValues() where the setPosition(self._position) is failing because it already thinks that the position is at 0. Hence the attempt to move to the starting position before the animation commences is being ignored. This causes the brief flicker.

You can fix it by replacing GTween:swapValues() in gtween.lua:

function GTween:swapValues()
	if not self._inited then
		self:init2()
	end
	local o = self._values;
	self._values = self._initValues;
	self._initValues = o;
	for n,v in pairs(self._rangeValues) do
		self._rangeValues[n] = -v
	end
 
	-- AWB 12/Sep/2012
	-- Fix for bug where swapValues causes a jump in the animation. 
        -- The problem is caused by setPosition() ignoring the requested
        -- change if it doesn't think the position has actually changed. 
        -- Since, after a swap, we are no longer really at position 0 we can
        -- force the set by clearing out the calculatedPosition cache.
        --
	self.calculatedPosition=nil
        --
	-- End fix
 
	if self._position < 0 then
		local pos = self.positionOld
		self:setPosition(0)
		self._position = self.positionOld
		self.positionOld = pos
	else
		self:setPosition(self._position)
	end
end

@atilim, if you are the guardian of gtween.lua in the Gideros release, perhaps you can check this over and make the change in a future release?

Best regards

ar2rsawseen · September 2012

Nice, can you push it to github?
https://github.com/gideros/GTween

bowerandy · September 2012

@ar2rsawseen, I don't have write access to that repository; doesn't the owner have to grant it (or push it themselves)?

Best regards

atilim · September 2012

@bowerandy thank you for both bug report and fix

I'll merge this changes.

On the other hand, let me test this case with original GTween. I wonder if it also has this bug.

atilim · September 2012

@bowerandy The same bug also exists in original GTween and your fix perfectly solves the problem. I've updated Github. Thanks again.

bowerandy · September 2012

@atilim, great. You know this bug has irked me for weeks. It never seemed quite serious enough to get around to fixing it but really attention to detail is everything.

Best regards

atilim · September 2012

Exactly. On the other hand, I've started to find GTween a little bit inefficient and bloated. Maybe it's time to port another tweening library to Gideros as an alternative. Here, TweenJS (from the same author) can be a good option:
http://www.createjs.com/#!/TweenJS
https://github.com/CreateJS/TweenJS/

It's also under the MIT license and I think it's more understandable and cleaner then GTween.

alexzheng · September 2012

cheer

ar2rsawseen · September 2012

What makes TweenJS a better otpion? How can you tell if it's more efficient?

atilim · September 2012

@ar2rsawseen I just find its API more intuitive:

var tween = Tween.get(myTarget).to({x:300},400).set({label:"hello!"}).wait(500).to({alpha:0,visible:false},1000).call(onComplete);

And after a quick look, TweenJS's setPosition function seems faster then GTween's. But I don't know exactly and there won't be big difference in either case.

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