Light scattering as post process

Why as a post processing effect?

There is more than one way to implement light scattering, or god rays, the most popular being through physically based volumetric rendering.
To choose which one to base my implementation on, I had to compare certain criteria:
- Implementation complexity - I had very limited time for the project.
- Visual appeal - of course the effect had to look good
- Performance - the effect should run real-time
I ended up choosing the screen-space method as it would take the shortest time to implement, which was the most important criteria for me.

Light scattering through physical volumes	Light scattering though post process
Pros: Physically accurate results Supports dynamic media and shadows Cons: Computationally expensive Harder to implement and tune	Pros: Very fast and GPU-friendly Simple to implement Ideal for sun shafts or stylized visuals Cons: Not physically accurate Only works for visible light sources

I followed two sources for this:
- GPU Gems 3
- Nicolas Menzel's post
I had to omit some steps, such as bloom, to save time.
Since I wanted to use in-engine lights, I added a light rendering pass, which uses the radius and world position of point lights and renders them in screen-space.

Iterates through each point light, stepping toward the light source while sampling and fading the scene’s brightness using decay and weighting factors.
Accumulates the light contributions, adds them to the original scene, and applies an exposure-based brightness adjustment.