Controls at which offset a GlowingOverscrollIndicator draws.
A positive offset will move the glow away from its edge,
i.e. for a vertical, leading indicator, a paintOffset of 100.0 will
draw the indicator 100.0 pixels from the top of the edge.
For a vertical indicator with leading set to
false, a paintOffset
of 100.0 will draw the indicator 100.0 pixels from the bottom instead.
A negative paintOffset is generally not useful, since the glow will be clipped.
This has no effect on a StretchingOverscrollIndicator.
double paintOffset = 0.0;