paintBack method
Paints the part of the frame behind the slices.
Implementation
@override
void paintBack(Canvas canvas, WheelFrameGeometry geometry) {
final g = geometry;
final _Layout f = _Layout(g);
if (shadow) WheelFrame.paintDropShadow(canvas, g, g.outer);
WheelFrame.paintPlate(canvas, g, f.trimOuter, plateColor);
}