func makeFragments(radius int, self bool) (frags []fragment) {
r := float32(radius)
for y := -r; y <= r; y++ {
for x := -r; x <= r; x++ {
d := math32.Hypot(x, y)
var includePoint bool
if self {
// Self is hollow ring
includePoint = r*0.9 <= d && d <= r*1.1
} else {
// Aliens are solid circles
includePoint = d <= r
}
if includePoint {
// Impart radial velocity to fragment
var vx, vy, extra float32
if d > 0 {
vx, vy = x/d, y/d
extra = 0.4
} else {
vx, vy = 0, 0
extra = 1.4
}
// Random non-radial component
uy, ux := math32.Sincos(rand.Float32() * (2 * math32.Pi))
frags = append(frags, fragment{
x,
y,
vx + ux*extra,
vy + uy*extra,
})
}
}
}
return frags
}
// euler returns e raised to the power iθ.
func euler(θ float32) complex64 {
y, x := math32.Sincos(θ)
return complex(x, y)
}