Generate this kind of 2d burst or pulse

Hi, I'm currently trying to develop a game using Cocos2d-x using C++
I really need to generate this burst or (donut-shaped) pulse.
I'm having a difficult time how to generate such shape.

At first, I was thinking of scaling the image but that didnt work out because the line or "diameter" of the donut shape gets bigger accordingly.. LOL

Any experienced coders who can provide an equation of this thing? or maybe "mathematics" is more exact.
If you guys can provide ANY help, suggestion, or alternative recommendation, I'll be so glad^^

https://www.youtube.com/watch?v=ewnEE5mt1ZM

And how is this a Qt question? Doesn't Cocos2D have a forum for these kind of questions?