// Plot implements the plot.Plotter interface.
func (b *BarChart) Plot(c draw.Canvas, plt *plot.Plot) {
	trCat, trVal := plt.Transforms(&c)
	if b.Horizontal {
		trCat, trVal = trVal, trCat
	}

	for i, ht := range b.Values {
		catVal := b.XMin + float64(i)
		catMin := trCat(float64(catVal))
		if !b.Horizontal {
			if !c.ContainsX(catMin) {
				continue
			}
		} else {
			if !c.ContainsY(catMin) {
				continue
			}
		}
		catMin = catMin - b.Width/2 + b.Offset
		catMax := catMin + b.Width
		bottom := b.stackedOn.BarHeight(i)
		valMin := trVal(bottom)
		valMax := trVal(bottom + ht)

		// value point
		topx := catMin
		topy := valMax

		var pts []vg.Point
		var poly []vg.Point
		if !b.Horizontal {
			pts = []vg.Point{
				{catMin, valMin},
				{catMin, valMax},
				{catMax, valMax},
				{catMax, valMin},
			}
			poly = c.ClipPolygonY(pts)
		} else {
			pts = []vg.Point{
				{valMin, catMin},
				{valMin, catMax},
				{valMax, catMax},
				{valMax, catMin},
			}
			poly = c.ClipPolygonX(pts)

			topx = valMax
			topy = catMin
		}
		c.FillPolygon(b.Color, poly)

		var outline [][]vg.Point
		if !b.Horizontal {
			pts = append(pts, vg.Point{X: catMin, Y: valMin})
			outline = c.ClipLinesY(pts)
		} else {
			pts = append(pts, vg.Point{X: valMin, Y: catMin})
			outline = c.ClipLinesX(pts)
		}
		c.StrokeLines(b.LineStyle, outline...)
		// show the value of each bar on top of it
		strvalue := fmt.Sprintln(ht)
		ft, _ := vg.MakeFont(plot.DefaultFont, 10)
		c.FillText(draw.TextStyle{Color: color.Black, Font: ft}, vg.Point{X: topx, Y: topy}, strvalue)

	}
}