samples/geometry/geometry.go
func FillStyle(gc draw2d.GraphicContext, x, y, width, height float64) {
	sx, sy := width/232, height/220
	gc.SetLineWidth(width / 40)

	draw2dkit.Rectangle(gc, x+sx*0, y+sy*12, x+sx*232, y+sy*70)

	var wheel1, wheel2 draw2d.Path
	wheel1.ArcTo(x+sx*52, y+sy*70, sx*40, sy*40, 0, 2*math.Pi)
	wheel2.ArcTo(x+sx*180, y+sy*70, sx*40, sy*40, 0, -2*math.Pi)

	gc.SetFillRule(draw2d.FillRuleEvenOdd)
	gc.SetFillColor(color.NRGBA{0, 0xB2, 0, 0xFF})

	gc.SetStrokeColor(image.Black)
	gc.FillStroke(&wheel1, &wheel2)

	draw2dkit.Rectangle(gc, x, y+sy*140, x+sx*232, y+sy*198)
	wheel1.Clear()
	wheel1.ArcTo(x+sx*52, y+sy*198, sx*40, sy*40, 0, 2*math.Pi)
	wheel2.Clear()
	wheel2.ArcTo(x+sx*180, y+sy*198, sx*40, sy*40, 0, -2*math.Pi)

	gc.SetFillRule(draw2d.FillRuleWinding)
	gc.SetFillColor(color.NRGBA{0, 0, 0xE5, 0xFF})
	gc.FillStroke(&wheel1, &wheel2)
}
func FillStyle(gc draw2d.GraphicContext, x, y, width, height float64) {
	sx, sy := width/232, height/220
	gc.SetLineWidth(width / 40)

	draw2dkit.Rectangle(gc, x+sx*0, y+sy*12, x+sx*232, y+sy*70)

	var wheel1, wheel2 draw2d.Path
	wheel1.ArcTo(x+sx*52, y+sy*70, sx*40, sy*40, 0, 2*math.Pi)
	wheel2.ArcTo(x+sx*180, y+sy*70, sx*40, sy*40, 0, -2*math.Pi)

	gc.SetFillRule(draw2d.FillRuleEvenOdd)
	gc.SetFillColor(color.NRGBA{0, 0xB2, 0, 0xFF})

	gc.SetStrokeColor(image.Black)
	gc.FillStroke(&wheel1, &wheel2)

	draw2dkit.Rectangle(gc, x, y+sy*140, x+sx*232, y+sy*198)
	wheel1.Clear()
	wheel1.ArcTo(x+sx*52, y+sy*198, sx*40, sy*40, 0, 2*math.Pi)
	wheel2.Clear()
	wheel2.ArcTo(x+sx*180, y+sy*198, sx*40, sy*40, 0, -2*math.Pi)

	gc.SetFillRule(draw2d.FillRuleWinding)
	gc.SetFillColor(color.NRGBA{0, 0, 0xE5, 0xFF})
	gc.FillStroke(&wheel1, &wheel2)
}
// FillStyle demonstrates the difference between even odd and non zero winding rule.