Perlin Lua

perlin.lua

local function mix(a, b, t) return (t * (b - a)) + a end
local function mod(a, b) return ((a % b) + b) % b end
local function fract(x) return x - math.floor(x) end
local function clamp(a, b, c) return math.min(math.max(a, b), c) end
local function dot(a, b)
    local s = 0
    for i = 1, #a do
        s = s + a[i] * b[i]
    end
    return s
end
local function sign(x) return x > 0 and 1 or (x < 0 and -1 or 0) end
local function pow2(a, b) return math.pow(math.abs(a), b) * sign(a) end
local function pal(i, r, g, b)
    i = i < 0 and 0 or (i > 15 and 15 or i)
    if r == nil and g == nil and b == nil then
        return peek(0x3fc0 + (i * 3)),
               peek(0x3fc0 + (i * 3) + 1),
               peek(0x3fc0 + (i * 3) + 2)
    else
        poke(0x3fc0 + (i * 3) + 2, clamp(b, 0, 255))
        poke(0x3fc0 + (i * 3) + 1, clamp(g, 0, 255))
        poke(0x3fc0 + (i * 3), clamp(r, 0, 255))
    end
end

local seed = {
    a = 500 + (math.random() * 1e4),
    fx = 500 + (math.random() * 1e4),
    fy = 500 + (math.random() * 1e4),
    px = math.random() - 0.5,
    py = math.random() - 0.5
}

local function pseudorandom2D(x, y)
    return fract(math.sin(dot({x + seed.px, y + seed.py}, {seed.fx, seed.fy})) * seed.a)
end

local function perlin(x, y)
    return mix(
        mix(
            pseudorandom2D(math.floor(x), math.floor(y)),
            pseudorandom2D(math.floor(x) + 1, math.floor(y)),
            fract(x)
        ),
        mix(
            pseudorandom2D(math.floor(x), math.floor(y) + 1),
            pseudorandom2D(math.floor(x) + 1, math.floor(y) + 1),
            fract(x)
        ),
        fract(y)
    )
end

local function f(x, y)
    x = x / 15
    y = y / 15
    local iterations = 4
    local sum = 0
    for i = 0, iterations - 1 do
        seed.a = 500 + (fract(math.sin((i + 0.512) * 512) * 725.63) * 1e4)
        sum = sum + perlin(x * (i + 1), y * (i + 1))
    end
    return sum / iterations
end