Overview

The NChartBrushScale class provides scale that transforms values into brushes like a step mapping function.
The scale contains array of reference values and array of brushes. It returns brush for given value according to these arrays:

brushes[n]
values[n - 1]
...
brushes[4]
values[3]
brushes[3]
values[2]
brushes[2]
values[1]
brushes[1]
values[0]
brushes[0]

This is equivalent to the following pseudo code:

if value <= values[0] return brushes[0];
if value > values[i] and value <= values[i + 1] return brush[i + 1];
if value > values[last] return brush[last]

So the array of brushes should contain n elements and array of values should contain n - 1. Values should be sorted (NChartBrushScale does not sort them automatically). If they are not, it can lead to strange results. If brush index goes out of range, nil is returned.