Bockit / mosaic-test

Coding test I had to do for a job application a while back. To build a mosaic in the browser from an image in a certain way

Photo mosaic

The goal of this task is to implement the following flow in a client-side app.

1. A user selects a local image file.
2. The app loads that image, divides the image into tiles, computes the average color of each tile, fetches a tile from the server for that color, and composites the results into a photomosaic of the original image.
3. The composited photomosaic should be displayed according to the following constraints:
   • tiles should be rendered a complete row at a time (a user should never see a row with some completed tiles and some incomplete)
   • the mosaic should be rendered from the top row to the bottom row.
4. The client app should make effective use of parallelism and asynchrony.

The project skeleton contains a lightweight server (written in node) for serving the client app and the tile images. Install the server dependencies with setup.sh, then run the server with start.sh. Those scripts assume a Mac environment, but are trivial enough to replicate on Linux if required.

  /              serves mosaic.html
  /js/*          serves static resources
  /color/<hex>   serves a mosaic tile for color <hex>.  e.g., /color/0e4daa

The tile server generates tile images, and caches them in memory; subsequent tile requests should be noticably faster.

The tile size should be configurable via the code constants in js/mosaic.js. The project skeleton is already set up to include those constants in both the mosaic client and the mosaic server. The default size is 16x16.

You should:

• pretend you're submitting this as production-quality code for review; i.e.,
  • write effective comments;
  • make the code modular;
  • make the code testable;
• use HTML5 features where appropriate;
• allocate about 3 hours to do the task.

You may:

• make minimal use of standard JS libraries (e.g., jQuery), since the goal of the exercise is to implement the flow yourself, not call out to someLibrary.makePhotoMosaic(...);
• edit /etc/hosts;
• use any HTML5 feature supported by current Chrome (e.g., Promise, Worker);
• be as creative as you like with the submission UI (file input, drag & drop, etc); however, it is not the focus of the task, a minimal UI is fine.

Have fun!