A fixed mask brush that creates a radial coverage mask.
The center sample has full coverage, the border samples have zero coverage. The coverage of the samples in-between is computed like this:
half = size / 2 value = max(0, half - length(x - half, y - half)) / half coverage = pow(value, power)
If power is
0, the following formula is used:
coverage = smoothstep(value)
smoothstep(x) is defined as
x * x * x * (x * (x * 6 - 15) + 10).