Mission Briefing

In this project we'll be building a simple but fun puzzle game in which a picture is scrambled and has to be unscrambled back to the original picture by sliding the different pieces around the board – a modern web-based take on a classic game from yesteryear.

Typically there is one blank space on the board and pieces can only be moved into this blank space so we will need to build a system that keeps track of where the blank space is, and only allows pieces directly adjacent to it to be dragged.

To give the player an incentive, we can also look at keeping track of how long it takes the player to solve the puzzle so that the player's best time can be recorded. The following is a screenshot that shows the final result of this project:

Why Is It Awesome?

Games are fun and they can keep people coming back to your site, especially a younger audience. Non-flash browser-based games are taking off in a big way, but getting into the action at the top end of the scale can have a steep learning curve.

A simple drag-based game like this is the perfect way to ease yourself into the gaming market without jumping straight in at the deep end, allowing you to hone your skills with some of the simpler concepts of game development.

This is also a great way to learn how to build a draggable interface in a precise and engaging format that is well suited to its intended purpose and intuitive to use. We can also look at some more advanced draggable concepts such as collision avoidance and precise positioning. We will also be learning how to interact with the localStorage API in order to store and retrieve data between sessions.

Your Hotshot Objectives

This project will be broken down into the following tasks, which we'll work through sequentially in order to produce a working end result:

• Laying down the underlying HTML

• Creating a code wrapper and defining variables

• Splitting an image into pieces

• Shuffling the puzzle pieces

• Making the puzzle pieces draggable

• Starting and stopping the timer

• Determining if the puzzle has been solved

• Remembering best times and adding some final styling

Mission Checklist

As well as jQuery, we'll also be using jQuery UI in this project, so now is the time to grab these libraries and put them in place. We can also take a moment to set up our project folder, which is where we can store all of the files that we'll create over the course of the book.

Create a new folder somewhere called jquery-hotshots. Within this folder create three new folders called js, css, and img. All the HTML pages we create will go into the root jquery-hotshots folder, while the other files we use will be distributed amongst the subfolders according to their type.

For the projects covered throughout the book we'll use a local copy of the latest version of jQuery, which at the time of writing is the brand new 1.9.0. Download a copy of the minified version from http://code.jquery.com/jquery-1.9.0.min.js and save it in the js folder.

Tip

It's considered best practice to use Google's content delivery network (CDN) to load jQuery and to link to the file without specifying a protocol. Using a CDN means the file is more likely to be in the visitor's browser cache, making the library much quicker to load.

It is also advisable to provide a fallback in the event that the CDN is not accessible for some reason. We can very easily use the excellent yepnope to load a local version of the script if the CDN version is not found. See the yepnope site, http://yepnopejs.com/, for more information on this and other resource-loading tips and tricks.

To download the jQuery UI components we'll require, visit the download builder at http://jqueryui.com/. We'll be using various other components in later projects, so for simplicity we can just download the complete library using the Stable button. The current version at the time of writing is 1.10.0.

Once the build has been downloaded, you'll need to grab a copy of the jquery-ui-x.x.x.custom.min.js file (where x.x.x is the version number) from the js directory inside the archive, and paste it into your js folder.

Tip

Recent versions of jQuery UI, as well as some of the more popular pre-built themes generated with Themeroller, are also available via Google's CDN.