func drawBackground(ctx *html.Context, delta float64) {
ctx.FillStyle = html.NewRGBColor(0, 19, 41)
ctx.FillRect(0, 0, 800, 480)
ctx.BeginPath()
ctx.ShadowBlur = 50
ctx.ShadowColor = html.NewRGBColor(220, 220, 220)
ctx.FillStyle = html.NewRGBColor(255, 255, 255)
ctx.Arc(
400+int(450*math.Cos(moonPosition)),
300+int(200*math.Sin(moonPosition)),
50, 0, math.Pi*2, false)
ctx.Fill()
moonPosition += delta * 0.001
ctx.ShadowBlur = 0
for i := 0; i < len(clouds); i++ {
c := clouds[i]
ctx.BeginPath()
ctx.FillStyle = html.Color("rgba(255, 255, 255, 0.2)")
ctx.Save()
ctx.Translate(int(c.X), int(c.Y))
for _, p := range c.parts {
ctx.Arc(p.X, p.Y, p.R, 0, math.Pi*2, false)
ctx.ClosePath()
}
ctx.Fill()
ctx.Restore()
c.X += c.Speed
if c.X > 820 {
c.parts = c.parts[:0]
c.init()
c.X = -100
}
}
}