Posts Tagged android

Posted on Programming

Heaps/Hashlink on Android

I wrote Hexlock using Haxe and Heaps, which went quite well – until I decided to compile it for Android. But it’s there now and we can all relax. Aside from getting Heaps setup to compile on Android, I ran into a few other issues.

  1. Touch event coordinates were wildly inflated

This made it seem like my interaction events weren’t going through at all (because in a sense they were not), but I tracked this back to touch events being multiplied by 10,000. They come in as a value between 0 and 1, and I discovered that they’re multiplied by windowWidth (which makes sense), but then divided by something called TOUCH_SCALE. It turns out I needed to add -D hl_ver=1.12.0 to my compile.hxml file to get it to use the appropriate TOUCH_SCALE.

2. I wanted to trigger vibration on Android

So I did. Click here to if you want to know how: triggering vibration on Android in Heapse/Hashlink.

3. Handling the back button

If you’re playing, the back button should take you back to the level select screen. If you’re at the level select screen, it should do what the back button does on Androids and minimize the app. And now it does! If you want to know how, check out dealing with the Android back button for Heaps/Hashlink.

4. hxd.Save didn’t work out-of-the-box

At this point I was too tired (lazy) to dig into why, so I just implemented my own method of saving using Android shared preferences. It seems to work! If you’d like to learn how, click here: saving data for Android with Heaps/Hashlink.

Again, I am not saying these are the best, correct, or even good ways to handle those issues. They’re just what I did, and they worked for me.

Posted on Programming

Heaps/Hashlink saving data for Android

When I was making Hexlock, I was disappointed but not overly surprised to find that hxd.Save didn’t work out-of-the-box on Android. It’s quite possible that it would have after some simple changes, but at that point I was too tired to dig through source files to try to discover why and what those changes may be.

So I just implemented my own method of saving using Android shared preferences.

The first step was to load and store data differently when compiling for Android, which wasn’t too bad because I already had my own wrapper to handle that. A lot of this will contain code specific to Hexlock, which you can ignore or not at your discretion. Basically I keep a map of levels (JSON strings) to score data, load it once when the game starts, and save the entire map out on a new high score.

public static function loadSaves():Void {
	var defValue = new Map<String, Highscore>(); // The default value
	#if android
		var bytes = Main.load(getInstance().name); // These are hl.Bytes
		var data = @:privateAccess String.fromUTF8(bytes); // Convert it to a String

		// This is 100% overkill but a wise man once said:
		// It is better to just throw in random possible values
		// than to wait for Android Studio to finish compiling and check 
		// what they actually are.
		if (data.length == 0 || data == "null" || data == null) { 
			// Welp, at least we have the default value
			getInstance().data = defValue;

		// This code is basically taken from hxd.Save
		var obj : Dynamic =;

		// set all fields that were not set to default value (auto upgrade)
		if( defValue != null && Reflect.isObject(obj) && Reflect.isObject(defValue) ) {
			for( f in Reflect.fields(defValue) ) {
				if( Reflect.hasField(obj, f) ) continue;
				Reflect.setField(obj, f, Reflect.field(defValue,f));
		getInstance().data = obj; // That's our data now            
		// If it's not for Android, just use hxd.Save
		getInstance().data = Save.load(defValue, getInstance().name);
public static function save(level:Level, highschore:Highscore) {
	getInstance().data.set(Json.stringify(level), highscore); // Add the score
	#if android
		var data =;, data);
	#else, getInstance().name);

For both save() and loadSaves() hxd.Save is used, except when compiling to Android, because I added -D android to my compile-to-c.hxml. There may already be a hlNative one #shrug. I didn’t see one, and adding -D android was easy enough.

You can see from above that the code requires the function, String) and Main.load(String); getInstance().name is just a constant string identifier like ‘my_cool_highscore_file’.

Since those functions are only referenced when compiling for Android, they only need to be defined when compiling for Android, which is convenient because hl.Bytes isn’t available on non-hashlink targets.

And in Main.hx:

#if android
public static function save(name:String, data:String) {}

#if android
public static function load(name:String):hl.Bytes { var i = 4; return hl.Bytes.fromValue("null", i); }

Who knows if I needed a body for load(String) – not me – but it worked, so I didn’t look into it further.

When compiling to C code for Hashlink, calls to the function get replaced with Java_io_heaps_android_HeapsActivity_save(), which I defined in my jni.c1 file, and of course an equivalent transformation happens to Main.load().

JNIEXPORT vbyte* JNICALL Java_io_heaps_android_HeapsActivity_load(vstring *name) {
	(*jvm)->AttachCurrentThread(jvm, &thisEnv, 0); //this is important to avoid threading errors
	jclass cls = (*thisEnv)->FindClass(thisEnv, "io/heaps/android/HeapsActivity");
	jmethodID method = (*thisEnv)->GetStaticMethodID(thisEnv, cls, "loadData", "(Ljava/lang/String;)Ljava/lang/String;");

	char *cname = hl_to_utf8(name->bytes);
	__android_log_print(ANDROID_LOG_DEBUG, "JNI.c", "loading... %s", cname);

	// Is this necessary? Who knows! Better safe than seg fault though.
	char *buf = strdup(cname);
	jstring jstrBuf = (*thisEnv)->NewStringUTF(thisEnv, buf);

	jstring result = (*thisEnv)->NewStringUTF(thisEnv, "null");
	if (method > 0)
		result = (jstring) (*thisEnv)->CallStaticObjectMethod(thisEnv, cls, method,jstrBuf);
	char *cresult =   (*thisEnv)->GetStringUTFChars(thisEnv, result, 0);
	__android_log_print(ANDROID_LOG_DEBUG, "JNI.c", "returned... %s",cresult);

	free(buf); // Free the string
	return cresult;

JNIEXPORT jstring JNICALL Java_io_heaps_android_HeapsActivity_save(vstring *name, vstring *data) {
	(*jvm)->AttachCurrentThread(jvm, &thisEnv, 0); //this is important to avoid threading errors
	jclass cls = (*thisEnv)->FindClass(thisEnv, "io/heaps/android/HeapsActivity");
	jmethodID method = (*thisEnv)->GetStaticMethodID(thisEnv, cls, "saveData", "(Ljava/lang/String;Ljava/lang/String;)V");

	char *cname = hl_to_utf8(name->bytes);
	char *cdata = hl_to_utf8(data->bytes);

	char *bname = strdup(cname);
	char *bdata = strdup(cdata);

	__android_log_print(ANDROID_LOG_DEBUG, "JNI.c", "saving %s: %s", bname, bdata);

	jstring jname = (*thisEnv)->NewStringUTF(thisEnv, bname);
	jstring jdata = (*thisEnv)->NewStringUTF(thisEnv, bdata);

	if (method > 0)
		(*thisEnv)->CallStaticVoidMethod(thisEnv, cls, method, jname, jdata);


To find out more about where thisEnv and jvm come from, check out triggering vibration on Android from Heaps/Hashlink.

Haxe strings come through Hashlink as vstrings, and the JNI uses jstrings, so you can see me converting between the two, above. Onload I just send back the char* instead of dealing with transforming it back into a vstring, and handle that in Haxe (which you can see even further above). Is this a memory leak? Who knows! Not me. But if it is, oh well – the load function is only called once during the apps lifetime.

As you can see, the C code assumes there will be saveData() and loadData() functions in, and there will be, because we’re about to add them!

static public void saveData(String name, String data) {
	SharedPreferences sharedPref = getContext().getSharedPreferences(name, Context.MODE_PRIVATE);
	SharedPreferences.Editor editor = sharedPref.edit();
	editor.putString(name, data);

static public String loadData(String name) {
	SharedPreferences sharedPref = getContext().getSharedPreferences(name, Context.MODE_PRIVATE);
	return sharedPref.getString(name, "null");

Above you can see that I just use name for both the SharedPreferences file and for the key in it. Whoops, that’s embarrassing. I could have used another string defined in the java, or just omitted specifying a name completely but it works and that’s good enough for me.

If you want to find out more about the files I’m referencing (including a Git repo hosting them), you can do so here: Hello World; Heaps on Android.

Posted on Programming

Dealing with the Android back button for Heaps/Hashlink

I wanted the back button on Android to work in a reasonable way for Hexlock: If you’re playing, the back button should take you back to the level select screen. If you’re at the level select screen, it should do what the back button does on Androids, and minimize the app.

It turns out that different versions of Android send different key codes with the event when you hit the back button, (and I also wanted to support Esc and Backspace on keyboard), so I matched a few of them.

var g = new LevelSelect();
sceneManager.requestMainMenu = function() {
	var s = sceneManager.switchScene(g);
	if (s == g) {
		trace("Already on the main menu, exit game");

hxd.Window.getInstance().addEventTarget(function(event : hxd.Event) {
	switch(event.kind) {
		case EKeyUp: 
			// backspace and escape; the last one is what my android sends for back
			if (event.keyCode == 8 || event.keyCode == 27 || event.keyCode == 1270)
		case _: // Match the rest

Then I added a static function exitapp() to my Main class, the idea being that it would do nothing unless I was compiling for Android. (I added -D android to my compile-to-c.hxml for just this purpose). There may already be a hlNative one, but who knows at this point. I didn’t see one, and adding -D android was easy enough.

#if android
public static function exitapp() : Void { }

When compiling to C code for Hashlink, calls to the function Main.exitapp() get replaced with Java_io_heaps_android_HeapsActivity_exitapp(), which I defined in my jni.c1 file.

JNIEXPORT void JNICALL Java_io_heaps_android_HeapsActivity_exitapp() {
	(*jvm)->AttachCurrentThread(jvm, &thisEnv, 0);
	jclass cls = (*thisEnv)->FindClass(thisEnv, "io/heaps/android/HeapsActivity");
	jmethodID method = (*thisEnv)->GetStaticMethodID(thisEnv, cls, "callbackExit", "()V");
	if (method > 0)
		(*thisEnv)->CallStaticVoidMethod(thisEnv, cls, method);

To find out more about where thisEnv and jvm come from, check out triggering vibration on Android from Heaps/Hashlink.

As you can see the C code assumes there is an callbackExit() function in, and there is, because I added one!

public static void callbackExit() {
	Intent intent = new Intent(Intent.ACTION_MAIN);

And that seemed to work! Even better, it didn’t crash.

If you want to find out more about the files I’m referencing (including a Git repo hosting them), you can do so here: Hello World; Heaps on Android.

Posted on Programming

Presenting Hexlock, a really fun game™

Hexlock, a simple counting-based puzzle game, now available for your Android device.

Select a level, defeat it, and repeat.

There are twenty-one levels in total, each represented by a different tile on the level select screen, and you can play them in whichever order you like.

In each level, you start by clicking the middle tile. From there, just form a path from neighbour to neighbour until the two numbers at the top match up. Once they do, you’ve won!

The hex tiles each have a value, represented in hexadecimal. The goal is in binary. All you need to do is form a path such that the hex values add up to the binary goal. You can do that by adding and converting between bases in your head, or, you know, just click around until it unlocks.

Once you’ve defeated a level, how well you did will be reflected in that level’s tile on the level select screen. Grey if you have yet to complete the level; green if you scored par or under; blue if you scored under 2 par; orange for less than 3 par; or red if your path was longer than 3 par.

Only your highest score for each level will be saved, and if you ever want to review that path, long press the hexagon for that level in the level select.


  • Clicking on the most recently selected hexagon will unselect it.
  • Press and hold (long press) the middle tile to reset your current level.
  • Press and hold (long press) a level to load your highest scoring path.
  • Press the back button on your phone, or escape or backspace on a keyboard to return to the level select menu.

Download it today in the Google Play store!


Or, if you don’t have an android device, you can play the web version here.

1. This is not true; very few people rate things in hexagons these days

Posted on Programming

Hello World; Heaps on Android

Hello, and welcome.

As there’s no way for you to reasonably know, I built a puzzle game recently – in Haxe, using Heaps which I had only used once before, for a website that required a 3D can. Which may seem strange, but I assure you it made sense at the time. Anyway, Heaps seemed fairly nice, so I figured I should try it again.

But I wanted it to be an Android app.

Which is okay, because Heaps works on Android. It says it right there on the website! Unfortunately, there’s not much info on it beyond that, and compiling Heaps for Android turned out rather less straight forward than I had hoped.

Fast forward five days of debugging Android Studio configurations and C code, and I now have a simple Heaps app running on Android. And it’s on GitHub!

It’s built based on a couple of repos1, 2, the second of which was particularly helpful, but I had to mix and match some things between them.

I don’t intend to keep it up-to-date unless I have a use for it, but it works as of November 11, 2022.

How it works

The Haxe code lives in app/src/main/haxe. It’s a basic Heaps hello world project set up for VS Code, as described in the documentation section of the Heaps site. There’s a compile.hxml file which tells the compiler to place the generated C code in the out/ directory of the cpp folder.

The C code lives in app/src/main/cpp. It contains git submodules to some of the necessary libraries, as well as a CMakeLists.txt. Android Studio uses that during its build process. You can find out more about the other things there at the link, above.

This is also where the JNI function for the heaps app lives (in jni.c).

The Java code lives in app/src/main/java, is the entry point to the Heaps hello world and triggers it to run. It extends which handles a bunch of the SDL stuff. Add your own classes as necessary if you want, I probably won’t!

Each of those directories contains a readme with some info about what they contain.

One important note: The NDK version.

It didn’t work with any of the NDK versions I had installed. I ended up having to download r18b and use that. I placed it in the ndk/ folder of my Android SDK directory. You can find this under File > Project Structure, and then by clicking SDK Location.

So I placed it in C:\Users\Brad\AppData\Local\Android\sdk\ndk.

But that’s not all – apparently Android Studio expects the ndk version directory to be named a certain way, so I named mine 18.1.1.

The Android Studio project in the Git repo expects that, so if you name it something else, update build.gradle to reflect that.

After that it should just be a matter of clicking build in Android Studio.

Problems along the way

As you can imagine from the heading nearby I ran into so many problems along the way. So many problems, and so many android log statements.

But my memory is terrible, and Google found surprisingly few results, so I’m going to catalogue some of them here. You know, for next time. You should be able to ignore this portion, they should all be addressed already in the repo code.

OpenAL needs needed by not found.

I tried a bunch of things for this, but the solution turned out to be adding arguments -DANDROID_LD=lld to the app file.

hashlink/src/std/types.c error: undefined reference to 'hl_zalloc'

hl_zalloc is defined in hashlink/src/gc.c. I added that to CMakeLists.txt when building the Hashlink library.

fatal error: 'minimp3.h' file not found

Added hashlink/include/minimip3 to the target_include_directories for fmt.hdll, in CMakeLists.txt.

java unsupported major.minor version 52

I updated to Java 1.8.0.

E/EGL_emulation: eglCreateContext: EGL_BAD_CONFIG: no ES 3 support (and a bunch of other SDL / window creation errors)

These seemed to go away when I tracked down that Hashlink uses version 3.0 for mobile, added the appropriate declaration to my AndroidManifest.xml, and fiddled with the settings in the emulator. Honestly I’m not sure what ended up fixing these things because nothing did and then I restarted Android Studio and everything was magically working.

At which point I was just willing to accept that.