func (c *Critter) initAlienVelocity() {
// Choose random velocity
// This peculiar 2D distibution was in the original sources.
// It was probably an error, but is now traditional in Frequon Invaders.
// It biases towards diagonal directions
c.vx = math32.Cos(2*π*rand.Float32()) * velocityMax
c.vy = math32.Sin(2*π*rand.Float32()) * velocityMax
}
func init() {
Twang = makeSound(44100, func(i float32) float32 {
const ω = 110 * 2 * π / nimble.SampleRate
const nharmonic = 32
sum := float32(0)
for h := float32(1); h <= nharmonic; h++ {
sum += math32.Sin(ω*h*i) * math32.Exp(-i*0.00004*h)
}
return sum / nharmonic
})
n := len(Twang)
AntiTwang = make([]float32, n)
for i := range AntiTwang {
AntiTwang[i] = Twang[n-1-i]
}
sum := float32(0)
Broken = makeSound(44100, func(i float32) float32 {
r := (rand.Float32() - 0.5) * (1.0 / 16)
newSum := sum + r
if math32.Abs(newSum) < 1.0 {
sum = newSum
}
sum *= (1 - 1/32.0)
return sum * math32.Exp(-i*.0001)
})
Wobble = makeSound(44100, func(i float32) float32 {
return 0.25 * math32.Sin((440+44*math32.Sin(i*0.001))*i*(2*π/nimble.SampleRate)) * math32.Exp(-i*0.00005)
})
partials := [...]float32{0.56, 0.92, 1.19, 1.71, 2.00, 2.74, 3.00, 3.76, 4.07}
Bell = makeSound(44100, func(i float32) float32 {
const θ = 512 * 2 * π / nimble.SampleRate
sum := float32(0)
const n = float32(len(partials))
for j := range partials {
sum += math32.Sin(i * θ * partials[j])
}
return sum * (1.0 / n) * math32.Exp(-i*0.0001)
})
}