[Löve2D] trippy stuff

-- left click: move towards
-- right click: set center
-- wheel: rotation speed

-- play around with these values:
local pennum = 800 -- higher == more awesomeness but more lag
local mousegrav = 0.04 -- higher == higher attraction towards mouse
local rotation = 2 -- rotation speed
local fadeout = 0.2 -- higher == less after-image
local wobbly = 0 -- higher == more random target


local time = 0
local targetx = 401
local targety = 301

function hsl2rgb(h, s, l)
    local r, g, b = 0, 0, 0

    if s == 0 then
        r = l
        g = l
        b = l
    else
        local function hue2rgb(p, q, t)
            if t < 0 then t = t + 1 end
            if t > 1 then t = t - 1 end
            if t < 1/6 then return p + (q - p) * 6 * t end
            if t < 1/2 then return q end
            if t < 2/3 then return p + (q - p) * (2/3 - t) * 6 end
            return p
        end

        local q = (l < 0.5) and (l * (1 + s)) or (l + s - l * s)
        local p = 2 * l - q
        r = hue2rgb(p, q, h + 1/3)
        g = hue2rgb(p, q, h)
        b = hue2rgb(p, q, h - 1/3)
    end

    return math.floor(r * 255), math.floor(g * 255), math.floor(b * 255)
end

function love.load()
    -- love.graphics.setLineStyle("rough") -- ugly
    canvas = love.graphics.newCanvas()

    pens = {}
    for i = 1, pennum do
        pens[i] = {
            x = 400,
            y = 300,
            lx = 400,
            ly = 300
        }
    end
end

function love.draw()
    love.graphics.setCanvas(canvas)
    love.graphics.setColor(0, 0, 0, 255 * fadeout)
    love.graphics.rectangle("fill", 0, 0, love.graphics.getWidth(), love.graphics.getHeight())

    for i, v in ipairs(pens) do
        love.graphics.setColor(hsl2rgb(i / pennum, 1, math.min(time / 2, 0.5)))
        love.graphics.line(v.lx, v.ly, v.x, v.y)
    end

    love.graphics.setCanvas()
    love.graphics.setColor(255, 255, 255)
    love.graphics.draw(canvas, 0, 0)

    love.graphics.print("FPS: " .. love.timer.getFPS())
end

function love.update(dt)
    if wobbly ~= 0 then
        targetx = (targetx + (math.random() * 800) * wobbly) / (1 + wobbly)
        targety = (targety + (math.random() * 600) * wobbly) / (1 + wobbly)
    end

    if love.mouse.isDown("r") then
        targetx, targety = love.mouse.getPosition()
    end

    for i, v in ipairs(pens) do
        v.lx = v.x
        v.ly = v.y
        local x, y = v.x, v.y
        local r = math.cos(time * (i / pennum)) * rotation * dt * ((targetx / 800) + (targety / 600))

        local nx = targetx + (x - targetx) * math.cos(r) - (y - targety) * math.sin(r)
        local ny = targety + (x - targetx) * math.sin(r) + (y - targety) * math.cos(r)
        x = (x + nx) / 2
        y = (y + ny) / 2

        if love.mouse.isDown("l") then
            local mx, my = love.mouse.getPosition()
            --local nx = mx + (x - mx) * math.cos(r) - (y - my) * math.sin(r)
            --local ny = my + (x - mx) * math.sin(r) + (y - my) * math.cos(r)
            x = (x + mx * mousegrav) / (1 + mousegrav)
            y = (y + my * mousegrav) / (1 + mousegrav)
        end

        v.x, v.y = x, y
    end

    time = time + dt
end

function love.mousepressed(x, y, b)
    if b == "wd" then
        rotation = rotation - 1
    elseif b == "wu" then
        rotation = rotation + 1
    end
end

function love.keypressed(k)
    if k == "escape" then
        love.event.push("quit")
    end
end