The factor of [[Distance Attenuation]] due to atmospheric effects like fog.
[[../Math/Linear Transformation|Linear]] [[Distance Attenuation]]:
$\huge s = \frac{F- |\nu|}{F-N} $
Where $F$ is the [[../Math/Far Clipping Plane|Far Plane Z Value]], $N$ is the [[Near Clipping Plane|Near Plane Z Value]], and $|\nu|$ is the distance between the camera and the [[Fragment]].
You can also use a quadratic or exponential fog value:
$\huge s = \pa{\frac{F- |\nu|}{F-N}}^{2} $
$\huge s = \max\pa{e^{-\rho | \nu |}, 1} $
Where $\rho$ is the fog [[../Physics/Density|density]].
You can then use the attenuation factor to blend with the original color of the [[Fragment]].
$\huge
C_{} = \op{lerp}_{\odot}\pa{C_{\text{fog}}, C_{\text{fragment}}, s}
$