How can I make a glow effect please ?

I’d like to make an effect like this :
(Click on a country in the map and you’ll see an out glow effect)

I searched the internet for many times, but without fruit.

Is there something that can help ?
Should there not be a library implementing many drawing effects to be easily used on OpenGL applications ?

Thanks in advance.

(I am a C++ developer)

(not advanced at all, as you sound like a total beginner in OpenGL)

Several ways :

  • render shape, blur, then draw white blurred version behind original. Well suited to static shapes/prerender/bake.
  • use a fragment shader to white-blur-sample in real time. Well suited to dynamic shapes.