// Draw a line with an angle with specified line cap and join
func Draw(gc draw2d.GraphicContext, cap draw2d.LineCap, join draw2d.LineJoin,
x0, y0, x1, y1, offset float64) {
gc.SetLineCap(cap)
gc.SetLineJoin(join)
// Draw thick line
gc.SetStrokeColor(color.NRGBA{0x33, 0x33, 0x33, 0xFF})
gc.SetLineWidth(30.0)
gc.MoveTo(x0, y0)
gc.LineTo((x0+x1)/2+offset, (y0+y1)/2)
gc.LineTo(x1, y1)
gc.Stroke()
// Draw thin helping line
gc.SetStrokeColor(color.NRGBA{0xFF, 0x33, 0x33, 0xFF})
gc.SetLineWidth(2.56)
gc.MoveTo(x0, y0)
gc.LineTo((x0+x1)/2+offset, (y0+y1)/2)
gc.LineTo(x1, y1)
gc.Stroke()
}