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When using Screen Space Direction Occlusion(SSGO) related techniques, such as Screen Space Global Illumination(SSGI), what is the commonly used attenuation function? I read from some materials that talk about attenuated by $d^2$ ($d$ is the distance between reflect point and receive point), how to explain this attenuation function from the perspective of PBR .

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  • $\begingroup$ Do you have a specific reference for SSGO/SSGI? These seem to be generic terms that can refer to a whole host of effects. (please correct me if I am wrong) $\endgroup$
    – pmw1234
    Commented Aug 6, 2021 at 11:54

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There is a slight confusion regarding the attenuation as a phenomenon and attenuation as a function of distance. They are very much related. Basically as you move away from a source of light, the light passing through some sort of medium, looses some of its energy either through absorption or diffraction. This phenomenon is the attenuation, the function computes to what extent this phenomenon is happening, that is to what extent the light looses its energy as it is passing through a medium.

According to Foley, et. al, Computer Graphics Principles and Practices, 2013, p. 376. You should be using the $1/d^2$ if you want to approximate physical behaviour.

For non physical behaviour other formulas are also provided for example see, id. p. 383.

Where does $1/d^2$ come from ? According to wikipedia:

Attenuation is linearly dependent on the medium length and attenuation coefficient, as well as – approximately – the frequency of the incident ultrasound beam for biological tissue (while for simpler media, such as air, the relationship is quadratic).

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