func drawClockPane(ctx *canvas.CanvasRenderingContext2D, r int) {
ctx.Save()
// cycle
ctx.StrokeStyle = "black"
ctx.LineWidth = 4
ctx.BeginPath()
ctx.Arc(0, 0, r, 0., float32(2*math.Pi), true)
ctx.ClosePath()
ctx.Stroke()
// hour tick
itv := 2 * math.Pi / 12.0
r0 := float64(r - 10)
r1 := float64(r)
for i := 0; i < 12; i++ {
angle := float64(i) * itv
ctx.MoveTo(int(r0*math.Sin(angle)), int(r0*math.Cos(angle)))
ctx.LineTo(int(r1*math.Sin(angle)), int(r1*math.Cos(angle)))
ctx.Stroke()
}
// minute tick
ctx.LineWidth = 2
itv = 2 * math.Pi / 60.0
r0 = float64(r - 5)
r1 = float64(r)
for i := 0; i < 60; i++ {
angle := float64(i) * itv
ctx.MoveTo(int(r0*math.Sin(angle)), int(r0*math.Cos(angle)))
ctx.LineTo(int(r1*math.Sin(angle)), int(r1*math.Cos(angle)))
ctx.Stroke()
}
ctx.Restore()
}
