So there is a new FXs on the scirra store, where i did the store artwork for.
Use this on any object with varying opacity. WebGL makes it efficent and simple to use!
How to use it?

Put it as an effect on a sprite,
Change parameters (either via editor or event sheet).

Parameters available to change

Alpha threshold,
Lower/Upper alpha clamps,
Smoothness factor for alpha.

[IMAGE: https://steemitimages.com/DQmchPWVVqWgvMM52ZHZPbvPZVHMVCDvh51V68vyHBPsBVa/ezgif-3-dc2c024ac7.gif]

[IMAGE: https://steemitimages.com/DQmQAGshQoDS6Va2CyA2jrRXh2SXDvNMF4ZAriqTo88eV4M/AC-720x320.png]

Get it here:
https://www.scirra.com/store/construct2-effects/smooth-alpha-clamp-4163