Pixel Tween

var i = index - 1, frame = timeToFrames(time), length = 40;
var row = Math.floor(i / 16), col = i % 16;
var transition = 10 + row * 4 + 2 * i;
var slow = 300, stop = 350;
var startX = 71 + 40 * col, endX = 800;
var startY = 240 + 40 * row;
if (frame < slow) {
    endY = 400 + 40 * i - 8 * frame;
} else if (frame > stop) {
    endY = 400 + 40 * i - 4 * slow - 4 * stop;
} else {
    var m = 400 + 40 * i - 8 * slow, n = 400 + 40 * i - 4 * slow - 4 * stop, o = -8 * (stop - slow), p = 0;
    var a = 2 * m - 2 * n + o + p, b = -3 * m + 3 * n - 2 * o - p, c = o, d = m;
    var x = (frame - slow) / (stop - slow);
    endY = Math.round(a * x * x * x + b * x * x + c * x + d);
}
if (frame < transition) {
    [startX, startY];
} else if (frame > transition + length) {
    [endX, endY];
} else {
    var t = (frame - transition) / length;
    var perc = -2 * t * t * t + 3 * t * t;
    [startX + perc * (endX - startX), startY + perc * (endY - startY)];
}