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stacklife

Conway's Game of Life for a Stack Exchange profile. See a deployed implementation on my Stack Overflow profile.

While the client-side markdown is designed to fit inside of a Stack Exchange profile, this code could easily be used in any HTML environment that allows links and images.

Example

The example below is fully interactive.

  Controls:
  Step Random Noise
  Clear Random Feature
  Click a cell to toggle it.
  View source

Server setup

  1. After downloading the code, run npm install inside the project directory to install Express.

  2. In lifeserver.js, change the profileUrl variable to the URL of the HTML page that will display the Life grid.

  3. Optionally, to enable HTTPS, copy your SSL cert/key files into the directory and uncomment the HTTPS code at the top of lifeserver.js.

  4. Run node ifeserver.js (with sudo if necessary to listen on ports 80 and 443).

Client setup

  1. In client.md, replace each instance of ${host} with the scheme and hostname of your server, with no trailing slash, e.g., http://example.com.

  2. If deploying to Stack Exchange, ensure your hostname is short enough to fit in the 3000 character limit. Also, you can save space by using // as the scheme (e.e., //example.com instead of http://example.com) which will use the scheme of the containing page. (Note that this means that your server must support HTTPS whenever Stack Exchange upgrades to HTTPS, or if a user is using HTTPS Everywhere.)

  3. Copy the contents of client.md to your profile or other page.

How it works

The server maintains the global state of the Life game. The client HTML/markdown displays the state of each cell as an image in a grid. An HTTP server listens for requests with particular paths:

  • /00 (or any two numbers) - serve an image representing the state of the cell at that {row,col} position (black for live, white for dead)
  • /w00 (or any two numbers) - toggle the state of the cell at {row,col}
  • /c - clear all cells
  • /r - fill cells with random noise
  • /f - clear cells and draw a random feature (glider, oscillator, etc.)
  • /s - step into the next Life generation

All requests redirect back to the profile page after they perform their specified server-side action (except for the /00 request, which serves an image instead of performing a redirect).

Future work

Future modifications might include:

  • using cookies to allow each user to have a separate game state
  • using query strings in the profile URL (passed to the server via Referer header) to have saved states sharable via URL
  • applying the general principles to a completely new game (chess, minesweeper, etc.). This would work especially well for a game with very few inputs and output that can be rendered as a single image, since multi-image output requires a high volume of separate HTTP requests. For example, a video game console simulator with a D-pad and a few buttons, plus a single screen image, rendered server-side with Imagemagick, would only require a few HTTP requests.