compute-sdk-python/examples/game-of-life.py at b1e49f208851aeda70db70ffa90aeecc1fc9d623 · fastly/compute-sdk-python · GitHub

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from base64 import urlsafe_b64decode
from random import random

from flask import Flask

try:
    from fastly_compute.wsgi import WsgiHttpIncoming
except ImportError:
    # We're running this using the Flask debug server.
    running_under_compute = False
else:
    running_under_compute = True


app = Flask(__name__)


# Board width and height. We assume a square board for now. If you change this,
# change the f"{i:010000b}" format string below to be the new value squared.
WIDTH = HEIGHT = 50


def decompressed_board(compressed: str) -> str:
    """Decompress the board representation sent from JS, returning a B&W board
    string ("10011011"...).

    Viceroy will pass us no more than 1936 bytes of the board. (Or maybe the
    entire URL gets truncated at 1965b.) This overcomes that (for the board
    sizes we're interested in).

    :arg compressed: A urlsafe_b64encode()d representation of the bit-packed
        black-and-white board. (We don't need color info in order to compute the
        next board.)

    This saves 83% space. RLE would save about 90% but would depend on the board
    and would be slower to compute.
    """
    if compressed == "none":
        return "none"
    i = int.from_bytes(urlsafe_b64decode(compressed))
    return f"{i:02500b}"


@app.route("/board/<compressed_board>")
def board(compressed_board: str):
    """Return the next frame of the Game Of Life, given the current one. If "none"
    is given instead, return a new random board."""
    cells = decompressed_board(compressed_board)

    # Random board on start:
    if cells == "none":
        return "".join("1" if random() < 0.1 else "0" for _ in range(HEIGHT * WIDTH))

    # Otherwise, evolve 1 step:
    new_cells = ""
    for i in range(len(cells)):
        new_cells += new_cell_color(cells, i)
    return new_cells


def new_cell_color(cells, cell_index):
    """Compute the new color of a single cell at the given offset."""
    count = sum(
        (cells[neighbor_index] != "0") for neighbor_index in neighbors(cell_index)
    )
    if cells[cell_index] != "0":
        if 2 <= count <= 3:
            return str(count)
        else:
            return "0"
    elif count == 3:
        return "1"
    return "0"


def xy_neighbors(x, y):
    """Return an iterable of the x-y coordinates of all the adjacent cells,
    omitting any that are outside the board bounds."""
    x_can_grow = x + 1 < WIDTH
    y_can_grow = y + 1 < HEIGHT
    x_can_shrink = x >= 1
    y_can_shrink = y >= 1
    if x_can_grow:
        yield x + 1, y
    if x_can_shrink:
        yield x - 1, y
    if y_can_grow:
        yield x, y + 1
    if y_can_shrink:
        yield x, y - 1
    if x_can_grow and y_can_grow:
        yield x + 1, y + 1
    if x_can_grow and y_can_shrink:
        yield x + 1, y - 1
    if x_can_shrink and y_can_grow:
        yield x - 1, y + 1
    if x_can_shrink and y_can_shrink:
        yield x - 1, y - 1


def neighbors(cell_index):
    """Return an iterable of the indices of all the adjacent cells, omitting any
    that are outside the board bounds."""
    y, x = divmod(cell_index, WIDTH)
    for neighbor_x, neighbor_y in xy_neighbors(x, y):
        yield neighbor_y * WIDTH + neighbor_x


@app.route("/")
def root():
    return """<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width,
                                   initial-scale=1.0">
    <title>Conway's Game of Life</title>
</head>
<body>
    <svg style="width: 100%%" viewBox="0 0 %(viewbox_width)s %(viewbox_width)s" id="grid" xmlns="http://www.w3.org/2000/svg">
    </svg>
    <p style="color: gray; font-weight: bold; font-family: sans-serif; text-align: right;"><span id="fps">…</span> <span style="font-size: 75%%">FPS</span></p>
    <script defer>
        const colors = {"0": "white",
                        "1": "#E44DA2",
                        "2": "#86E9C9",
                        "3": "#A577DF"};
        let board = "none";
        const max = %(width)s;
        let recent_boards = ["", "", "", "", "", "", ""];
        let boredom_counter = 0;
        let fps = 0;

        // Draw a square grid of circles, and return a 2D array of them.
        function initGrid() {
            let svg = document.getElementById("grid");
            let grid = [];
            for (let y = 0; y < max; y++) {
                row = [];
                grid.push(row);
                for (let x = 0; x < max; x++) {
                    let circle = document.createElementNS("http://www.w3.org/2000/svg", "circle");
                    circle.setAttribute("cx", 5 + x * 10);
                    circle.setAttribute("cy", 5 + y * 10);
                    circle.setAttribute("r", 4.5);
                    circle.setAttribute("fill", "white");
                    svg.appendChild(circle);
                    row.push(circle);
                }
            }
            return grid;
        }

        // Compress the board, shucking off color info and interpreting the
        // remaining 1s and 0s as binary digits. Interpret as an int, and
        // encode using URL-safe base64.
        function compressedBoard(board) {
            if (board == "none") {
                return "none";
            }

            // Collapse to black-and-white:
            let binary = board.replace(/2|3/g, "1");

            // Pad to multiple of 8 bits if necessary:
            binary = binary.padStart(Math.ceil(binary.length / 8) * 8, "0");

            // Convert binary string to bytes:
            const bytes = [];
            for (let i = 0; i < binary.length; i += 8) {
                const byte = binary.slice(i, i + 8);
                bytes.push(parseInt(byte, 2));
            }

            // Convert bytes to URL-safe base64:
            let ret = "";
            const base64Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

            for (let i = 0; i < bytes.length; i += 3) {
                // Get next 3 bytes:
                const byte1 = bytes[i] || 0;
                const byte2 = bytes[i + 1] || 0;
                const byte3 = bytes[i + 2] || 0;

                // Pack them into a 24-bit number:
                const combined = (byte1 << 16) | (byte2 << 8) | byte3;

                // Pull out four 6-bit values:
                const char1 = base64Chars[(combined >> 18) & 0x3F];
                const char2 = base64Chars[(combined >> 12) & 0x3F];
                const char3 = i + 1 < bytes.length ? base64Chars[(combined >> 6) & 0x3F] : "=";
                const char4 = i + 2 < bytes.length ? base64Chars[combined & 0x3F] : "=";

                ret += char1 + char2 + char3 + char4;
            }
            return ret;
        }

        async function updateGrid(grid) {
            // Fetch new grid:
            // These days, max querystring URL length is 65K in Firefox. Only Edge is shorter, at 2083.
            board = await (await fetch("./board/" + compressedBoard(board))).text();

            // Draw it:
            let i = 0;
            for (let y = 0; y < max; y++) {
                for (let x = 0; x < max; x++) {
                    grid[y][x].setAttribute("fill", colors[board[i++]]);
                }
            }

            fps += 1;
        }

        // If we've seen this board configuration a bunch of times recently,
        // clear the board and start with a fresh one.
        function assuageBoredom() {
            for (recent_board of recent_boards) {
                if (board == recent_board) {
                    boredom_counter += 1;
                    break;
                }
            }
            recent_boards.shift();
            recent_boards.push(board);
            if (boredom_counter >= 10) {
                board = "none";
                // Has to be at least 7 long to detect the union of 3-tick and
                // 2-tick oscillators going at it:
                recent_boards = ["", "", "", "", "", "", ""];
                boredom_counter = 0;
            }
        }

        // Main loop
        async function startAnimation(grid) {
            await updateGrid(grid);
            assuageBoredom();
            animationId = requestAnimationFrame(function() { startAnimation(grid) });
        }

        function startFpsCounter() {
            el = document.getElementById("fps");
            const secs = 3;
            function updateFpsReadout () {
                el.textContent = Math.round(fps / secs);
                fps = 0;
                setTimeout(updateFpsReadout, secs * 1000);
            }
            setTimeout(updateFpsReadout, secs * 1000);
        }

        function main() {
            let grid = initGrid();
            startAnimation(grid);
            startFpsCounter();
        }

        main();
    </script>
</body>
</html>
""" % {"width": WIDTH, "viewbox_width": 10 + WIDTH * 10}


if running_under_compute:
    HttpIncoming = WsgiHttpIncoming(app, reuse_sandboxes_for_ms=300)