HXP Projects && Template Directories

If you look closely at the OpenFL “docs” page, you’ll notice it lists two options under “project files.” The first of the two is the XML format you know and love, or at least know, but what’s up with the second?

Before I answer that question, I have some questions for you to answer.

Is your project file getting out of hand? Do you wish the XML format supported string manipulation? Do you find yourself typing out multiple <set> tags to simulate the “or” operator? Have you ever tried and failed to copy a directory with the <template> tag?

If you answered “yes” to any of these questions, HXP files may be right for you. Consult your physician today!

So anyway, what are HXP files? The short answer is, they’re HX files with an extra P.

The P stands for “Project,” so the long answer is, they’re project files which let you use Haxe instead of XML. You can write functions, manipulate strings, declare variables, and even access Haxe’s standard library.

Let’s try it out!

Ok, find a sample project that uses an HXP file, and… oh. There aren’t any, are there?

Fine, we’ll use DisplayingABitmap. I’ve created an HXP version of the project file, available here. Save it as project.hxp, delete project.xml, and you’re ready to give it a try.

Lime recognizes the file format, so just run lime test flash and it’ll find the new project file. It should show the OpenFL logo in the middle of the screen.

Congratulations! Through no fault of your own, you have gotten an HXP project file to work!

Converting your XML file to HXP

Running a sample project is all well and good, but what about that much larger project file you want to convert? Or perhaps that large file that you don’t want to convert because it will be so much work, but you have to convert anyway? Either way works.

To start, let’s reduce the amount of typing you need to do. Haxe has a wonderful feature known as “functions” (you may have heard of them), and I’ve written a set of functions that match some of the tags used in XML project files. Paste them at the end of project.hxp so that you don’t have to scroll past them each time.

Here’s a conversion guide:

If that isn’t enough, or if I got something wrong, refer to the source. (Also be sure to let me know.)

One step at a time

If this is too much work to do all at once, then keep your old project file around, and import it into the new one:

With that done, you’re free to move items over one at a time. Just be warned that some features, such as the <template> tag for folders, may quit working correctly. If this happens, focus on converting them first.

OpenFL Template Basics: Overriding AndroidManifest.xml

What do you do if you need to change AndroidManifest.xml, and OpenFL’s customization options aren’t enough? Sure you can add permissions using <config:android permission="android.permission.WHATEVER" />, and change the app title, and so on…

But what if you want to support multiple screen sizes? You need to include a <supports-screens> tag, or Google may hide your app from tablet users! This is yet another of the billions of scenarios that OpenFL fails to account for. (Sheesh, OpenFL dev team, get a move on.)

What you need is full control of the AndroidManifest.xml, but if you change it in the Lime project, it’ll just get reverted when you update to a new version. And making an extension for this is just plain overkill.

Creating Your Own Manifest File

Before you can worry about overriding AndroidManifest.xml, you’re going to need something to replace it with. Ideally something as similar as possible, to avoid breaking anything. Start by getting a copy of Lime’s template file. (For the record, if you want to replace a different template file, search this folder.)

Save your copy of AndroidManifest.xml somewhere in your project. I suggest making a “templates” folder for files like this, but you can put it wherever. Open up your copy of the file and add the following right before </manifest>:

Using Your Manifest File

Finally! Enough preparation, it’s time to circumvent the natural order and impose our will upon OpenFL! No longer shall we be bound by the constraints imposed upon us! Together we shall rise up, take control, and-

What’s that? “Get on with it”? Oh fine…

Type this in your project.xml file:

Which Files Can be Overridden?

To answer this question, first compile your project for Android, and open Export/android/bin (or bin/android/bin). Take a good look – everything the light touches is your kingdom. By which I mean you can override the files in that folder.

However, you need to make sure put your file in the same folder as the file you’re overriding. GameActivity.java is located in app/src/main/java/org/haxe/lime, so you’d put this in project.xml:

OpenFL Extensions

For the most part, OpenFL does an excellent job of providing you with the features you need in a platform-independent manner. It tells you the screen size, loads your assets, and even maps Android’s back button to the escape key.

Unfortunately, the OpenFL dev team cannot think of everything. Maybe you want to adjust the screen brightness on Android. Or the music volume. Maybe you want access to the camera on iOS. Or maybe you need to integrate a custom library used internally at your company, which the OpenFL dev team could not possibly have integrated for you.

For simplicity, I’ll be using screen brightness as an example. Setting this can be done in only 1-3 lines of code on both iOS and Android. The catch is, neither of those examples are in Haxe, and there’s no way to convert them to Haxe. If only you’d written the app “normally” rather than using OpenFL, you could just copy-paste those few lines of code, and you’d be done! But no, you wanted luxuries like cross-platform compilation, and now you have to somehow use Haxe code to invoke functions in Objective-C and Java.

Fun Fact

Did you know, when you compile for Android, OpenFL creates a complete, self-contained Android project, and then tells the Android SDK to compile that? And when compiling for iOS, it creates an Xcode project, and then has Xcode do the remaining work?

You can see for yourself by checking your output folder (probably either bin or Export; I’ll assume the former). Dig into bin/android/bin, and you’ll find all the files and folders you’d expect to find in a normal Android project. You could even, if you felt bold enough, modify the project, and compile it directly using the Android SDK. (Warning: Don’t actually do this! OpenFL will almost certainly overwrite your changes.)

The same applies to iOS – after compiling, you can check out bin/ios/bin to see the project that OpenFL created. You could try modifying this too, but again, OpenFL is going to revert your changes. There has to be a better way.

Creating an Extension

The OpenFL team is well aware of this problem, and in their infinite wisdom they created the “extension” feature. Also in their infinite wisdom, they wrote no documentation whatsoever before moving on to the next feature.

Extensions are basically mini-projects consisting of native (or Java) code, as well as Haxe bindings. You include them in your project, and then you can call the native (or Java) code by calling the Haxe bindings. Let’s look at an example.

Start by running the following:

I’m calling it “SetBrightness” because that’s all we’ll be doing here. You can call it something else.

Open up the folder, and you’ll find the following structure:

  • haxelib.json – Allows you to submit to Haxelib.
  • include.xml – Like project.xml in your main project, this tells OpenFL what to do with all the other files here.
  • SetBrightness.hx – Contains Haxe bindings for your Java and C++ functions. At first, everything in here will be sample code.
  • dependencies/
    • android/ – An Android library to be included in your Android builds. This is what lets you include Java code. All files in this folder are processed as templates, so you can use that syntax.
      • build.gradle – A project file for this Android library. Leave this alone unless you’re familiar with Gradle.
      • src/ – Despite the name, you can’t just put source files in here. They actually go in a child folder.
        • main/
          • AndroidManifest.xml – The manifest file for your Android library. If your extension requires permissions, this is the place to put them.
          • java/ – Java source files go here.
            • org/haxe/extension/
              • SetBrightness.java – The recommended place for your Java code. It comes with useful callbacks for monitoring the activity lifecycle, or you can ignore all that and write static functions.
  • ndll/ – When you compile your C++ code, the result will go in here.
    • Linux/
    • Linux64/
    • Mac/
    • Mac64/
    • Windows/
  • project/ – The root folder for your C++ project.
    • Build.xml – Build file for your C++ project. Only files named here (or included from those named here) will be compiled.
    • common/ – C++ source files (but not header files) go here.
      • ExternalInterface.cpp – Registers your C++ functions, allowing SetBrightness.hx to access them.
      • SetBrightness.cpp – Put C++ code here, based on the sample code that starts here.
    • include/ – C++ header files go here.
      • Utils.h – Header file for SetBrightness.cpp. Functions must be declared here in order for ExternalInterface.cpp to access them.

Writing Code for Android

Click through all the folders under dependencies/ until you reach SetBrightness.java. Add the following code:

That’s all well and good, but how do you call this function? The answer… is JNI. *Dramatic thunder crashes* Actually, it’s not that bad if you’re only dealing with one function. Climb your way back to the root SetBrightness/ folder, and add this to SetBrightness.hx:

That’s still a little much. Fortunately, shoe[box] came up with an easier way. Start by including the “inthebox-macros” library in your project, change the package in SetBrightness.hx to org.haxe.extension, and add @:build(ShortCuts.mirrors()) just before the class declaration. Now the code above can be replaced with this:

All that’s left is to include the extension in your project (see below), and you can call SetBrightness.setBrightness(0.8); from Haxe.


When you try to use this extension on Android, you’ll run into a few errors. First, a compile error:

This happens because you aren’t compiling an ndll for Android, but by default Lime expects you to. To fix the error, go into include.xml and replace <ndll name="SetBrightness" /> with <ndll name="SetBrightness" unless="android" />.

Next, you’ll get a runtime error:

(The only thing that matters about this error message is that it contains the word “thread.” When developing an OpenFL extension, all thread-related errors have the same solution.)

On Android, some tasks have to be done on the main thread. When you use JNI, it runs on a thread other than the main one. Fortunately, Extension.callbackHandler.post() lets you get back to the main thread.

This function takes a Runnable object, so you’ll have to create one of those. Take all the code in your function, and put it inside the run() function:

(Remember, you only need to do this if you get a thread-related error. Usually, it isn’t worth the trouble.)

And that’s it for Android. On to iOS!

Writing Code for iOS

You’ll notice that the extension is set up for C++ code, but to access system properties like brightness, you need to use Objective-C code. Fortunately, this part’s easy: just change the .cpp file extensions to .mm. You’ll also need to update their names in Build.xml. And because Objective-C is specific to iOS, I suggest disabling them for everything else.

If you need C++ code on other platforms, just disable the C++ files on iOS:

Now to write some actual Objective-C code! Put this in SetBrightness.mm:

Now update Utils.h:

Don’t forget to update ExternalInterface.mm:

Last but not least, create the Haxe bindings in SetBrightness.hx:

Phew! That was a lot of updating. [Edit: inthebox-macros can generate the Haxe code, and I wrote a utility to generate ExternalInterface.mm and Build.xml.]

Time to compile!

Including the Extension

Almost done! All that’s left is to include it in your project.

This can actually be done in two ways. The easy way works if you’re only using one machine, or if the relative path is the same on all machines (for example, if the extension project is contained within your main project). All you have to do is add this to your project.xml or application.xml file:

The slightly harder way is to register it with Haxelib by running the following from the root of the extension:

Then include it: