function love.load()
    love.window.setTitle("Julia Set")
    love.window.setMode(1024, 576)
    width, height = love.graphics.getDimensions()
    maxIter = 120
    zoom = 1.2
    offsetX, offsetY = 0.0, 0.0
    t = 0
    paused = false
    shader = love.graphics.newShader[[
        extern float zoom;
        extern float ox;
        extern float oy;
        extern float time;
        extern number maxIter;

        vec4 effect(vec4 color, Image tex, vec2 tc, vec2 sc)
        {
            float x = (sc.x - 512.0)/256.0 * zoom + ox;
            float y = (sc.y - 288.0)/256.0 * zoom + oy;
            float zx = x;
            float zy = y;
            float cx = 0.285 + 0.3*cos(time*0.3);
            float cy = 0.01 + 0.3*sin(time*0.3);
            int i;
            for(i = 0; i < int(maxIter); i++){
                float xt = zx*zx - zy*zy + cx;
                zy = 2.0*zx*zy + cy;
                zx = xt;
                if(zx*zx + zy*zy > 4.0) break;
            }
            float v = float(i)/maxIter;
            vec3 col = 0.5 + 0.5*cos(6.2831*(vec3(1.0,0.5,0.2)*v + vec3(time*0.05,0.2,0.0)));
            return vec4(col,1.0);
        }
    ]]
end

function love.update(dt)
    if not paused then
        t = t + dt
        shader:send("time", t)
        shader:send("zoom", zoom)
        shader:send("ox", offsetX)
        shader:send("oy", offsetY)
        shader:send("maxIter", maxIter)
    end
end

function love.draw()
    love.graphics.setShader(shader)
    love.graphics.rectangle("fill", 0, 0, width, height)
    love.graphics.setShader()
    love.graphics.setColor(1, 1, 1)
    love.graphics.print("Julia Set", 10, 10)
    love.graphics.print("Zoom: "..string.format("%.2f", zoom), 10, 30)
    love.graphics.print("Iter: "..maxIter, 10, 50)
    love.graphics.print("Time: "..string.format("%.1f", t), 10, 70)
    love.graphics.print("[W/S]: Zoom  [A/D]: Move  [↑/↓]: Iter  [Space]: Pause", 10, 550)
end

function love.keypressed(key)
    if key == "escape" then love.event.quit() end
    if key == "space" then paused = not paused end
    if key == "w" then zoom = zoom * 0.9 end
    if key == "s" then zoom = zoom / 0.9 end
    if key == "a" then offsetX = offsetX - 0.1*zoom end
    if key == "d" then offsetX = offsetX + 0.1*zoom end
    if key == "up" then maxIter = math.min(maxIter + 10, 500) end
    if key == "down" then maxIter = math.max(maxIter - 10, 20) end
end