The original project can be found here. And the following is a brief introduction by the original author:
Open source (BSD) extension for built-in Unity lights. It uses ray marching in light's volume to compute volumetric fog. This technique is similar to the one used in Killzone (GPU Pro 5: Volumetric Light Effects in Killzone Shadow Fall by Nathan Vos)
Corresponding thread in Unity Forum can be found here.
I added a few lines of code, namely creating new script VolumetricLightProjector.cs and new shader VolumetricProjection.shader so that the light volume can be multichromatic, which resulted in:
The following gif is rendered with the camera lying inside the light volume and the spotlight is rotating along its local axis.
To use this multichromatic light volume, attach VolumetricLightProjector.cs instead of VolumetricLight.cs to the lights that you want to create this effect on. And then add a colored image as light projection texture.
The idea of my algorithm is: When performing raymarching in light's volume, we sample the color from light projection texture. Color are accumulated on the way to achieve the final output color.