I spent some time recently to figure out GWT’s new super dev mode. What is super dev mode?
In GWT, you had two modes of running your app so far. You could either start it in dev mode or compile it and deploy it to a web server for testing.
The official docs are a bit sparse, so i figured i’d provide a tutorial on how to setup your libgdx project to use GWT super dev mode. Be warned, the process is a bit involved at the moment.
I started out by generating a project via the setup-ui, then load it into Eclipse. You can do the following on existing projects as well of course. My initial setup looks like this:
All changes will be made to the HTML project!
Modifying the gwt.xml file
First we have to change the linker options on the gwt.xml file of the HTML project, located in project-html/src/your/package/here. You should see something like this:
Put those two files into your project-html/war folder, right next to the index.html file. Should look like this:
Now include those two files into your index.html file, like this:
... rest of index.html
Configuring and starting the code server
To start the code server, it’s easiest to create a new Run Configuration in Eclipse. Go to Run -> Run Configurations…, then create a new Java Application run config.
Give it a nice name (mygame code server), and as Project, set your html project. As main class specify com.google.gwt.dev.codeserver.CodeServer. This class is responsible for compiling the code and serving it to the browser.
The class is found in a jar file of the GWT SDK, so we need to add that to the classpath of the Run Configuration. Go to the Classpath tab, select User Entries, then click the Add External Jars… button
You can find the jar gwt-codeserver.jar file in your Eclipse installation folder
Finally we need to specify the arguments to the code server. It wants to know where our sources are, and which GWT module to compile. We need to tell it about the gdx-sources.jar, the gdx-backend-gwt-sources.jar, the core project’s src/ folder and the src/ folder of the HTML project itself. The code server doesn’t like jar files, so we have to unzip them in their respective directories (project-core/libs/gdx-sources.jar, project-html/war/WEB-INF/libs/gdx-backend-gwt-sources.jar), ending up with this:
Now we can specify the arguments of the run configuration, html project, gdx gwt backend, gdx sources, and the core project’s sources:
Hit Apply then Run, and you should see this after 20 seconds:
Click the link at the bottom of the console output, which will open a browser and display this:
Drag the Dev Mode On bookmark to your bookmark bar (already done in the above screenshot). We’ll need to click on that later.
With this we have configured and started the code server. It can just sit there running while you code your game. You will have to redo the setup for every new project of yours.
Running the app in super dev mode
Now for the fun part. The code server only serves source maps and Java script code. We need to still host the index.html and asset files in the project-html/war folder through a webserver. I usually point Mongoose at my project-html/war folder. That will serve the war/ folder contents at http://localhost:8080/.
An alternative is to start the html project like we do in dev mode (right click project, Run As -> Web Application, click on the URL in the Development Mode view). The URL is usually something like http://127.0.0.1:8888/index.html?gwt.codesvr=127.0.0.1:9997, just remove the part after the ? to end up with http://127.0.0.1:8888/index.html
Once you opened the index.html in the browser (either served through a proper web server or dev mode), you will see this:
Click OK, then click on the “Dev Mode On” book marklet your previously added to the bookmarks bar of your browser. You’ll see this:
Now for the magic part. Bring up the developer tools of your browser. I use Chrome, which has super duper source map support, haven’t tested other browsers yet. In Chrome, you can press F12 or right click the site and click “Inspect Elements”. You’ll see this
Click on Sources, then click on the “Show Navigator” button:
This will bring up this view, expand the entries under localhost:9876, and there you have your Java code. Select one of your fails, e.g. your ApplicationListener, and set a break point, e.g. like this:
You can now inspect variables, see the call stack, step over/into statements and so on.
If you changed your source files, just click the “Dev Mode On” bookmarklet, click Compile and let things reload.
And that’s super dev mode. Hopefully the GWT team will add better integration, at the moment the setup is a bit convoluted.