Dialog Box - called from: Input2 Menu
Fog in the 3D drawing mode is similar to fading (Shading dialog) in the Standard drawing mode - it contributes to the illusion of depth by changing the color as a function of distance from the eye. It blends the specified foreground color for the atom, bond or other object with the given background or other specified color, on a pixel-by-pixel basis.
This can be according to one of three equations, selected with the radio buttons in the upper left of the dialog.
Linear: f = (end - z) / (end - start)
Exp: f = exp[-density * z]
Exp2: f = exp[(-density * z) ^2]
where z is the distance from the eye and f is the fraction of the initial color, the remainder being the fog color specified in the lower part of the dialog. Note that the color in this case is specified by RGB components varying from 0.0 to 1.0 (floating point) rather than 0 to 255.
ATOMS sets the parameters start and end at the foremost and rearmost atoms, or calculates the density, using the specified Fraction of intensity at rear. That is, the foremost atom will always have the pure (non-fogged) color (f = 1.0), and the rearmost atom will have the specified fraction (f) of the pure color and the remainder the fog color.
For example, if the rearmost atom is to blend into the background, i.e. disappear, set the Fraction of intensity at rear at 0.0 and check the Use background radio button. If the fog color is not the current background (Background Color dialog, Input2 Menu), it will usually be black (0.0, 0.0, 0.0).
Fog or fading may also be referred to as depth-cueing.