func drawPng(b *bytes.Buffer, p *plot.Plot, width, height float64) {
w, h := vg.Inches(width), vg.Inches(height)
c := vgimg.PngCanvas{Canvas: vgimg.New(w, h)}
p.Draw(plot.MakeDrawArea(c))
c.WriteTo(b)
}
func drawPng(b *bytes.Buffer, p *plot.Plot, width, height float64) {
w, h := vg.Inches(width), vg.Inches(height)
c := vgimg.PngCanvas{Canvas: vgimg.New(w, h)}
p.Draw(plot.MakeDrawArea(c))
c.WriteTo(b)
}