distance property
A value between 0.0 .. 1.0, defaulting at 0.6, that places the
"midpoint" for each color shading function in the Steps.
It is a percentage between the start and end of each step color to begin transitioning toward the color value with shadeFunction applied to it.
Imagine this represents the color red as a dark "shaded step" with
distance ~= 0.5 (note: each color and stop in a FooShadedSteps is
"quadruplicated", so this diagram accurately represents how each color
will be divided):
|-----------------+++++++++++++++++++++++|
[RED] . [RED] . [MIDPOINT] . [DARK RED]
Then imagine this represents the same scenario but distance ~= 0.25:
|--------++++++++++++++++++++++++++++++++++++++++++|
[RED] . [MIDPOINT] . [STILL BLENDING] . [DARK RED]
Implementation
final double distance;