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
}
// phaseColor computes RGB components for pure hue at given angle of color space.
func phaseColor(angle float32) (r, g, b float32) {
// j = index of hextant
if angle < 0 {
angle += 2 * π
}
j := int(3 / π * angle)
θ := angle
if j == 6 {
j = 0
θ = 0
}
// Red
switch j {
case 0, 1:
r = 1
case 2:
r = math32.Cos(1.5*θ - π)
case 3:
r = 0
default:
r = math32.Cos(1.5*π - .75*θ)
}
// Green
switch j {
case 0, 1, 2:
g = math32.Cos(π/2 - 0.5*θ)
case 3:
g = math32.Cos(1.5*θ - 3*π/2)
default:
g = 0
}
// Blue
switch j {
case 0, 1, 2:
b = 0
case 3:
b = math32.Cos(1.5*θ - 2*π)
default:
b = math32.Cos(.75*θ - π)
}
return
}