You can view the source code for any plugin tool in Whitebox simply by pressing the 'View Code' button on the tool's dialog. This code is however not live, in the sense that you cannot modify it and see changes in the program. To do this, you would need to go to the project's source code. If you are serious about developing for Whitebox you are going to want to access the source code.
Whitebox is currently hosted through a subversion repository on GoogleCode (http://code.google.com/p/whitebox-geospatial-analysis-tools/source/checkout). You can view the complete development version (i.e. the most current version of Whitebox) on this site. You can also download the code locally onto your computer. This can be done quite easily using an integrated development environment (IDE) such as Netbeans. You'll need to ensure that you have the Java Development Kit (JDK) 7.0 or higher installed on your machine (visit the Oracle Java site for instructions) and the latest version of the excellent Netbeans IDE. (It is likely the case that you could use an alternative IDE such as Eclipse, but the following instructions assume you are using Netbeans.)
In Netbeans, choose the Team->Subversion->Checkout. In the Repository
URL textbox, add the following:
http://whitebox-geospatial-analysis-tools.googlecode.com/svn/trunk/ whitebox-geospatial-analysis-tools-read-only
Then choose a local directory on your computer to download the
repository into. Notice that you will need to be connected to the
internet for this operaton. If you wish, you can request to be added
to the list of Whitebox developers, which would allow you to commit
changes to the source code.
Once the data has been downloaded, open all of the projects that are included. You'll see that there are at least 16 Whitebox projects, most of which are associated with specific toolboxes, e.g. GISTools, ImageProcessingTools, and StatsTools. The WhiteboxAPI and WhiteboxGIS projects are the most important. The WhiteboxAPI project contains all of the common classes and files that each of the other projects rely on. For example, this is where you will find the WhiteboxRaster and ShapeFile classes that allow the various plugin tools to access and manipulate raster and vector data. The WhiteboxGIS project is the site of the main Whitebox graphical user interface (GUI). Most of what you see when you run Whitebox is contained in this project. You will need to set the WhiteboxGIS as the main project by right-clicking over the project name in the Projects tab and selecting 'Set as Main Project'. This important step will tell Netbeans which project it should go to first when the user selects the run or debug buttons from the toolbar.
Before you can run Whitebox, however, there are a few things that you are going to have to set. First, if you go to the 'Files' tab on the upper left-hand corner, you will see that there is a folder within the WhiteboxGIS project called 'resources'. This is an important folder that contains many necessary files for Whitebox to run correctly. When you first launch Whitebox, it will look for this folder. Now, here is the confusing part. When you run Whitebox from Netbeans by either pressing the 'run' or 'debug' buttons, it is actually running a copy of the WhiteboxGIS.jar file that lives in: 'build'->'classes'->'whiteboxgis'. If you don't see that folder in your files tab yet, it's because Netbeans hasn't created it until you first try to run it. If the folder doesn't exist, then neither does the WhiteboxGIS.jar (which it will build when you try to run) and also, neither does the 'resources' folder. So, you'll need to select either run or debug. In doing so, expect it to fail this first time, simply because there is no 'resources' folder. However, this first run will create the necessary, 'build'->'classes'->'whiteboxgis' folder into which you can copy the 'resources' folder. This is perhaps a bit confusing...the files contained in that resources folder that you have within your WhiteboxGIS project are actually 'under Subversion', meaning that every time you modify any of these files, it wants to let the online repository know and vice versa. It actually contains a lot of hidden files to do this. You don't really want to copy these hidden files into the 'build'->'classes'->'whiteboxgis' folder, so instead you have to 'export' this directory into this location.
To export the 'resources' folder, first create a new empty folder within 'build'->'classes'->'whiteboxgis' called 'resources' (you can do this within Netbeans from the 'Files' tab). Now right-click over the resources folder that is within the WhiteboxGIS project (i.e. the one that is actually full of files) and select 'Subversion'-> 'Export...'. Now export the folder into your newly created 'resources' folder within 'build'->'classes'->'whiteboxgis'. I've probably made this sound more confusing that it really is.
That's it, you should now be able to run Whitebox. If you select debug and nothing happens, it may be the result of a property setting that is not suited to computers with limited RAM. Right-click over the WhiteboxGIS project in the Projects tab and select 'Properties'. Under the 'run' tab you will find the VM (virtual machine) option, -Xmx2g. This is essentially telling Netbeans to try to set the Java virtual machine (JVM) up to use 2GB of memory. If your computer only has 2GB of memory or less, this is going to be a problem. Simply lower the value (e.g. -Xmx500m) or delete the parameter all together and try to debug again. You should find that it works this time.
So there you go! You now have the Whitebox source code up and running on your computer. Now it's time to have some fun playing with the code. You can start by writing your own plugin tool (see tutorial on this topic). If you do write a tool, be sure to send it to me and I'll be happy to include it in the next version of Whitebox. Happy coding.