func drawOrientedLine(gc *draw2d.ImageGraphicContext, x, y float64, theta float64, r float64) {
c := math.Cos(theta)
s := math.Sin(theta)
gc.MoveTo(x-r*c, y-r*s)
gc.LineTo(x+r*c, y+r*s)
gc.Stroke()
}
func WhiteBG(gc *draw2d.ImageGraphicContext, xsize, ysize float64) {
gc.BeginPath()
gc.MoveTo(0, 0)
gc.LineTo(xsize, 0)
gc.LineTo(xsize, ysize)
gc.LineTo(0, ysize)
gc.LineTo(0, 0)
gc.Close()
gc.SetFillColor(color.RGBA{255, 255, 255, 0xff})
gc.Fill()
}
func DrawLine(gc *draw2d.ImageGraphicContext, x1, y1, x2, y2 float64) {
gc.MoveTo(x1, y1)
gc.LineTo(x2, y2)
gc.FillStroke()
}