colors.roy

// Generate a color palette RGB values. 
//
// Nice info on generating color palettes
// http://krazydad.com/tutorials/makecolors.php
//

type RGB = { red: Number, green: Number, blue: Number }

let prime_color_sequence (count: Number) (offset: Number) =
    let frequency = 0.3
    if count == 0 then
        nil
    else
        // let index = ((sine ((count * frequency) + offset)) / 180 * 127) + 128
        let index = ((Math.sin((count * frequency) + offset)) * 127) + 128
        Cons (index) (prime_color_sequence (count - 1) offset)

let zip_rgb (a: List Number) (b: List Number) (c: List Number) = 
    match a
        case Nil = nil
        case (Cons a1 as) = match b
                case Nil = nil
                case (Cons b1 bs) = match c 
                    case Nil = nil
                    case (Cons c1 cs) = Cons { red: a1, green: b1, blue: c1 } (zip_rgb as bs cs)
    
let color_sequence a = 
    let red = prime_color_sequence 64 0
    let green = prime_color_sequence 64 2
    let blue = prime_color_sequence 64 4
    zip_rgb red green blue