How GraLL 2 Glow works
Basically, the screen is rendered twice. Once ‘normally’, and once with a ‘glow pass’, to a ‘glow buffer’. In the glow pass, only glowing parts of the scene are rendered in their glow colour, anything else is rendered black (to occlude glowing stuff behind it, or things would glow through walls). Glowing objects can have a special ‘glow map’ texture. This texture is the one that’s rendered on them during the glow pass. The glow buffer is then blurred and added on to the normal render.
This is the normal red checkpoint texture:
This is the glow map:
It ends up looking like this in-game (the added red point light improves the effect):
Here’s an example glow pass render:
The brighter the colour on the glow map, the more is added, and the brighter it ends up looking. The glow pass is done without any lighting except ambient lighting. So, in effect, the ambient factor of the material can be used as a ‘glow amount’ property.