you can extract the brightest parts of an image and add a postprocessing filter to it:
original:

brightest parts:

example starglow:

result:


so you would need to render the view into a buffer, use some calculations (multiplication, pow , saturation methods) to it, then blur the result of this (as stars or just gaussian blur) and use this result to brighten the base(rendered view) . as usual this should be the texture of a screen aligned quad.


a gobo is some kind of projection texture, i mentioned this because you where talking about volumetric lights and the gobo-technique adds a lot. but you aren't talking about this as i know now