Returns the reduction, as a power of two, at which a viewer may resample the mask when it is drawn under
transform: the largest that still leaves samplesPerPixel samples per device pixel along
its most enlarged direction; each reduced sample is then the share of the samples it covers that paint (8-bit coverage).
public int GetReduction(in Matrix transform, double samplesPerPixel)
The transform from the unit square (user space, §8.9.4) to device pixels.
The fewest reduced samples per device pixel, at least 1 (see GetReduction(in Matrix, Double, PdfColorConverter?)).
ISO 32000-2 §8.9.6.2 and §8.9.6.3 (issue #362): coverage averages linearly, so reducing before painting equals the box filter of the rasterizer over the mask's own samples, to within rounding. For displaying only.